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n21roadie
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Radio card RX bandwidth?

Wed Mar 09, 2011 1:41 pm

I would like to ask a question about Mikrotik radio cards on channel bandwidth receive, for example if i use frequency scan from AP1 which is using 5320 and 20Mhz bandwidth, it shows signal strength of -24 @5700, -28@5865, -34@5200 from my other AP's on the tower will these signals effect the receive signal on AP1 at 5320, and is the bandwidth gain of the receive side of Mikrotik if set for 20mhz actually 20mhz or does it remain full spectrum bandwidth regardless of what channel has been selected?
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Re: Radio card RX bandwidth?

Sat Mar 19, 2011 8:28 pm

The question is also, is the transmitter only radiating within a 20MHz bandwidth or is it radiating more than this? So it could be the card is seeing what is really out there, or it could be the receiver is being overloaded and the signals are only inside the receiver?

The way to tell is to measure the level you're getting now, insert 10dB attenuation and see if the signal falls by 10dB or more. If more, then the signal being received is being generated within the receiver.

Reducing TX power on your other cards by say 3dB, does that cause the levels elsewhere on other frequencies also to fall by 3dB? If everything is 'real', then the others should also fall by 3dB. If they are spurii or intermods, they will change by a different amount or even disappear altogether.
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Re: Radio card RX bandwidth?

Mon Mar 21, 2011 12:45 am

My question was on the receive (listen) RX bandwidth, is it strictly @20Mhz -3db and could it be lets say -10 @40Mhz, etc
I am curious how steep the bandwidth roll off curve is and if this would have any effect on the performance of individual AP's on a tower having several sectoral AP's
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Re: Radio card RX bandwidth?

Mon Mar 21, 2011 2:09 am

If all you're interested to know is the theoretical rx bandwidth rolloff response figures of a particular card, you will have to research the manufacturer's datasheet for the particular card you are referring to. My point still stands. Further to that, what should happen in theory is often wholly different to reality. ETSI have a mask it should comply to, but each card will be better or worse at complying with that spectrum mask.

Therefore relying just on the receiver's theoretical selectivity performance to try to determine if interference will occur is not the only parameter that should be considered.
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Re: Radio card RX bandwidth?

Mon Mar 21, 2011 1:46 pm

If all you're interested to know is the theoretical rx bandwidth rolloff response figures of a particular card, you will have to research the manufacturer's datasheet for the particular card you are referring to......
thanks for your reply,but so far i have not seen any data about the receive bandwidth spec on the manufacturer's datasheets?
Therefore relying just on the receiver's theoretical selectivity performance to try to determine if interference will occur is not the only parameter that should be considered.
Maybe i should have expanded my question to include the antenna as well, for example when using sectoral AP antenna with full spectrum 5.8 bandwidth.

My thoughts are to move each AP in/out on the support arm on the mast while still being directed to the target coverage area for any reduction in signal from the other AP's on the mast (side lobes signal reduction)
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Re: Radio card RX bandwidth?

Mon Mar 21, 2011 5:05 pm

so far i have not seen any data about the receive bandwidth spec on the manufacturer's datasheets?
What is the specific card you are looking for data on?
Maybe i should have expanded my question to include the antenna as well, for example when using sectoral AP antenna with full spectrum 5.8 bandwidth.
Please expand what you mean by that statement.
My thoughts are to move each AP in/out on the support arm on the mast while still being directed to the target coverage area for any reduction in signal from the other AP's on the mast (side lobes signal reduction)
Always a wise decision to move antennae away from each other, but it depends on the antenna's characteristics as to whether a vertical or horizontal separation will give the greatest benefit.

Then of course, there are the coax feed cables, pigtails and separation of the whole RF path between different transmitters, including the cards themselves, earthing points.

BUT if a transmitter is generating RF outside of it's intended channel, or radiating on multiple channels due to some non-linearity, you can separate the bits as much as you like, you'll still have co-sited interference!
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Re: Radio card RX bandwidth?

Mon Mar 21, 2011 5:50 pm

What is the specific card you are looking for data on?
XR5 for starters?
Quote:
Maybe i should have expanded my question to include the antenna as well, for example when using sectoral AP antenna with full spectrum 5.8 bandwidth.

Please expand what you mean by that statement.
For example if as mentioned if the AP in question is using 5320, using a XR5 with a 16dbi full spectrum antenna, this AP in RX listen mode what will the received signal be at 5200, and 5260, from the other AP's all on the same polarity, there are other AP's also used on this mast but the frequencies are much further apart and some are horizontal.

BUT if a transmitter is generating RF outside of it's intended channel, or radiating on multiple channels due to some non-linearity, you can separate the bits as much as you like, you'll still have co-sited interference!
No - not generating rf outside it's assigned channel but if i could measure direct from the AP using a spectrum analyzer what is actually being picked up and at what level.
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Re: Radio card RX bandwidth?

Mon Mar 21, 2011 9:20 pm

The XR5 is based on the Atheros ROC. Therefore specific performance data is only available by directly contacting them. They are renown for not publishing any technical data beyond that which will sell their chips except to OEMs.

If you want to learn a little more on co-sited interference perhaps have a read of "Adjacent Channel Interference in Dual-radio 802.11a Nodes and Its Impact on Multi-hop Networking" by Harvard University.

Still not sure what a "full spectrum antenna" is exactly. Full spectrum would suggest DC to infinity. Do you actually mean an antenna designed to operate over a band of frequencies with a performance that is not necessarily consistent across that band, but is able to operate without too much return loss or too high a vswr so as to cause any serious issues for the transmitter? One that will have a widely varying gain figure, but the manufacturer always picks which ever one is the greatest gain figure, without telling you for which spot frequency that was for? One that is therefore listed by the manufacturer as being "5GHz band" or maybe even "5200-5800MHz"? :-)

Your example given is impossible to quantify as you have not provided enough data to calculate the interference figures. The amount of signal from one AP, being picked up by another on the same site, depends on many more factors than just the aerial type, polar diagram and gain.
no - not generating rf outside it's assigned channel
All 802.11 transmissions radiate RF outside their assigned channel. Especially so on 2.4GHz! (Because the radiated channel bandwidth is greater than the channel spacing). The amount radiated also depends on if the TX device is being operated outside it's published test parameters and if there any other non-linear devices in the vicinity, or connected to it (amplifiers for example).
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Re: Radio card RX bandwidth?

Mon Mar 21, 2011 10:10 pm

Still not sure what a "full spectrum antenna" is exactly.
- 16dBi 4.9-6.0Ghz Sectoral Gain, http://www.itelite.net/offer.php?n=36&lang=en
This antenna with a XR5, which if i assume correctly will receive equally any signal in the 4.9 to 6Ghz spectrum,
while in transmit cycle the bandwidth maybe 20Mhz but as soon as the radio card goes into receive mode, will the bandwidth be much wider,

Ok it follows that if used a limited bandwidth antenna's like say 5.4 to 5.7 would have a higher rejection to signals outside these frequencies but losing the flexibility to change frequencies outside the bandwidth.
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Re: Radio card RX bandwidth?

Tue Mar 22, 2011 2:19 am

Firstly the antenna given as an example of a "full spectrum bandwidth aerial" operating between 4.9 and 6.0 isn't. It is 'only' 5.1 to 5.9GHz.

It is also clearly only really resonant at the highest point of it's stated band coverage. Somewhere around 5.8GHz. Which is probably where the gain of 16dBi has been measured. At all other frequencies it is operating at less than peak performance. Not surprising given it's construction design. The sidelobes at +/-80 degs are quite high (around -20dB), meaning that if there were more than one on a mast, mounted side by side, they would cause RF to get into each other unless you could get them to be very far apart. But as this is clearly designed to be a CPE, this is unlikely at a Base Station as this would not be the right aerial to use for that. As a CPE unit it's fine and 'fit for purpose'.

Also the phrase "full spectrum" is meaningless. Like I said, "full spectrum" means exactly that, the full spectrum. I.e. DC to iffinity. a 800MHz bandwidth from approx 5.1-5.9GHz is clearly not "full spectrum". Probably better to describe it as "full 5GHz band" if you really wanted to call it anything at all.

The receiver will NOT immediately open up and thus "see" the whole band. The filtering is not done by the antenna bandwidth. It is done with a BAW resonator or in some cases with a single LPF in front of the LNA within the Receiver and software filtering using a FIR Digital filter. However, the better the filter characteristic, the longer the filter length, the longer the time taken for a signal to pass through it, thus the slower it performs, the worse the latency. Therefore it is always going to be a compromise between getting a filter mask to make it work and not too complex to affect the throughput performance. But the short version of the story is that the receiver filtering will be very nearly the same as the spectral mask used for the TX filtering.

There is something further to be taken into account and that is the AGC characteristic of the Receiver. Therefore when a receiver is picking up a strong signal, on channel, the gain of the LNA will be driven down so as to always keep the signal to around -40dBm (exact value depends on model) and therefore the co-channel response shape will improve and reduce co-channel interference.

So.. once again, here is another parameter that is required to be taken into account when trying to calculate if adjacent channel interference will occur or not!

The antenna will hardly offer any rejection at all of out-of-band signals (e.g. signals at 2-5Ghz or 6-8GHz). That role is nearly all down to the quality of the RF filtering and 3rd order IMD performance of the LNA of the wifi card. At out of band frequencies, the polar diagram changes significantly, for example at 4GHz, the main lobe may now be at 45degs from the centre line, admittedly with reduced gain, but it will still pick up the signals.

It is possible to obtain inter-digital filters or cavity filters to reduce co-channel interference, but these are large and if narrow enough to cover just one channel, are very expensive. It also means that if you need to operate on a different channel to that for which the filter is tuned for, you have to either retune the filter (a skilled process and time consuming, even WITH all the right equipment) or buy another one. I can recall working for a microwave company where my sole job was to tune 7GHz inter-digital cavity filters for a military contract, which had to have a flat response curve within +/-1dB over a 1 GHz band and it took 5 days to do just one!

Bottom line - what do you think the performance will be like when you only spend a few dozen bucks for a wifi card?! It's a miracle it works at all! :-)
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Re: Radio card RX bandwidth?

Tue Mar 22, 2011 3:02 am

rarely seen such an interesting topic! I think we all can learn from it. so I have some questions/remarks too:
It is also clearly only really resonant at the highest point of it's stated band coverage. Somewhere around 5.8GHz. Which is probably where the gain of 16dBi has been measured. At all other frequencies it is operating at less than peak performance.
Why is this? I would think it is the middle frequency. So a 5.4 to 5.7Ghz antenna would perform best at 5500Mhz?
Or lies the answer in the fact that the actuall 5Ghz band is devided in two parts. One lower and one upper part where the last is for outdoor use. Thus by designing antenna's for some frequency in the upper part it makes more sense than just the centre of the 5Ghz band spectrum? After all, who wants a 28dBi raster in his living room! :D
The receiver will NOT immediately open up and thus "see" the whole band. The filtering is not done by the antenna bandwidth. It is done with a BAW resonator or in some cases with a single LPF in front of the LNA within the Receiver and software filtering using a FIR Digital filter. However, the better the filter characteristic, the longer the filter length, the longer the time taken for a signal to pass through it, thus the slower it performs, the worse the latency. Therefore it is always going to be a compromise between getting a filter mask to make it work and not too complex to affect the throughput performance. But the short version of the story is that the receiver filtering will be very nearly the same as the spectral mask used for the TX filtering.

There is something further to be taken into account and that is the AGC characteristic of the Receiver. Therefore when a receiver is picking up a strong signal, on channel, the gain of the LNA will be driven down so as to always keep the signal to around -40dBm (exact value depends on model) and therefore the co-channel response shape will improve and reduce co-channel interference.
BAW resonator = ??
LPF = ??
LNA = ??
FIR Digital filter =??
AGC = ??
"co-channel response shape" = ??

I know we can all google for it, but it would make it much more readable, and thus learning, to have these terms explained here. Can you please add these to your further very interesting text?

Can you give us a better understanding of what the "length of the filter" is and why it is delaying the signal so much we would notice the increase in latency?

I am from the times when I as a sailor learned about radar technology, where the filtering was done with basically physical filtering of signals. I can remember something about electronic filtering in these days but must agree the theory behind all that in my head is pretty much gone, if not outdated....
3rd order IMD performance of the LNA of the wifi card.
IMD = ??
Bottom line - what do you think the performance will be like when you only spend a few dozen bucks for a wifi card?! It's a miracle it works at all! :-)
Ha! That's good one! Hence MT has so much problems getting nv2 properly to work in heavy crowded spectrum situations.
 
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Re: Radio card RX bandwidth?

Tue Mar 22, 2011 3:52 am

WirelessRudy - Thank you.
Why is this? I would think it is the middle frequency. So a 5.4 to 5.7Ghz antenna would perform best at 5500Mhz?
Because, looking at the VSWR response curve for the aerial given as an example, it definitely dips at around 5.8GHz. If you notice along the whole of the rest of the band it is waving up and down due to the multiple resonances of each of the component parts that make up the antenna design. I.e. each bit of the copper clad etching on the circuit board is slightly tuned (by design) to different segments of the band to broaden the original designed frequency it is really most resonant on. In this case, it would appear that it was originally for Band C (5.8GHz+/-) and was stretched downwards by adding more copper or slightly increasing some of the line lengths between them. We are of course, only talking about very tiny amounts of adjustments. But as I have no intimate knowledge of how this one was made, besides having taken one apart last year, it is difficult to be sure.

I would also expect to see the gain figure vary by around -2dBi to -3dBi across the band from the figure obtained at 5.8GHz. So if perhaps you were operating at 5.3GHz, the same aerial may be providing -14dBi gain and with a slightly different polar diagram even? I have seen aerials that have shifted their angle of fire by a few degrees depending on the frequency being used!

(I am also always deeply suspicious of any manufacturer's claims of an antenna gain unless they can guarantee that every aerial is tested rather than the first one they built in the R&D lab and sent away for testing. I have seen aerials claiming on paper one thing, but reality is a lot lower. I have see some Omni aerials that are physically much longer in length, making one think they have a higher gain, yet when you open them up, inside they contain the same identical copper wiring or PCB boards inside as their lower gain models! Once again - "you get's what you pays for")

Sorry about the acronyms, but this is my stock and trade.. OK

BAW : http://en.wikipedia.org/wiki/Electronic_filter
LPF : http://en.wikipedia.org/wiki/Low-pass_filter
LNA : http://en.wikipedia.org/wiki/Low_noise_amplifier
FIR Digital filter : http://en.wikipedia.org/wiki/Finite_impulse_response
AGC : http://en.wikipedia.org/wiki/Automatic_gain_control

co-channel response shape - that was a error. It should have read 'adjacent channel response shape'. Sorry for any confusion.

Anyway, "adjacent channel response shape" is a phrase made from "adjacent channel" i.e. I am referring to the response of the receiver on the adjacent channels. "response shape" refers to the receiver's selectivity curve. Or how fast the roll-off is in the receiver's performance at off-channel signals. Or in other words the shape of the selectivity filter. The faster the roll off, the greater the slope angle, the greater the attenuation of signals that are away from the centre frequency of the channel it is actually on. Filters also need to be wide enough to take the smaller and lower in level side lobes of the transmitted phase modulated signal. A Wifi signal does not generate all it's energy in a neat square shaped channel. There is a main peak in the middle, it may even be quite flat across the top (especially with 802.11n), but there is always energy contained further down on each side of that main lobe of energy which must not get filtered out as it is still an important part of the signal that is required to be processed.

"length of the filter". How many iterations the software program has to loop around. Obviously, the more times the software has to loop around the same piece of code, performing the computations, the longer the amount of time it will take for the answer to "pop" out the other end. Therefore the longer the period of time it takes from the time the signal arrived at the start of the filter to the time the signal is finished being processed at the 'other end'. Therefore the greater the latency. Also, there is only so much CPU power in these little chips, so any software needs to be optimised as well and compromises made!

It could be argued that hardware filtering is always better, as it requires no processing at all, being a natively inert process of 'just' using capacitance and inductance or reactance. However with the requirement for these boards to cover ever increasing bandwidths, those hardware filters will require tuning to enable them to cover the full band. To engineer into a design this auto-tuning under computer control is very difficult when dealing with microwaves and in turn, their millimetric wavelengths as everything interacts. Or in simple terms, it simply becomes a nightmare to design. Therefore by using software filtering, the costs are much reduced.

IMD : http://en.wikipedia.org/wiki/Intermodulation

My original training was as a Radio and Electronics Officer in the Navy, with Radar Maintenance, SOLAS and of course, Morse Code at a minimum of 25 wpm! So it appears we may have some similar backgrounds!
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Re: Radio card RX bandwidth?

Tue Mar 22, 2011 4:23 pm

The sidelobes at +/-80 degs are quite high (around -20dB), meaning that if there were more than one on a mast, mounted side by side, they would cause RF to get into each other unless you could get them to be very far apart.
About 1meter apart but was considering as the side lobes may vary from antenna to antenna to physically move the antenna while monitoring the signal levels from the other AP's for min signal,
But as this is clearly designed to be a CPE, this is unlikely at a Base Station as this would not be the right aerial to use for that. As a CPE unit it's fine and 'fit for purpose'.
What is the best AP antenna for price and performance for 5.8ghz?
Bottom line - what do you think the performance will be like when you only spend a few dozen bucks for a wifi card?! It's a miracle it works at all! :-)
Same question - what is the best radio card for price performance,
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Re: Radio card RX bandwidth?

Tue Mar 22, 2011 11:50 pm

About 1meter apart but was considering as the side lobes may vary from antenna to antenna to physically move the antenna while monitoring the signal levels from the other AP's for min signal,
You mean moving the antenna backwards and forwards horizontally? The other problem is the casing of that CPE is plastic. Therefore any RF from other APs will easily get into the sides and get directly into the wifi card and electronics. Electronics that have transistors, transistors that have semi-conductor junctions, which are non-linear when driven outside their operational spec and what does non-linear devices then in turn cause? Interference. IMD's and harmonics. That is why it is best to leave plastic boxed CPE devices to what they were designed for. For the CPE, where the chances of being near to other high levels of RF (in-band or out-of-band) are remote.
What is the best AP antenna for price and performance for 5.8ghz?
How long is the string and is it stretchable? OK, I know I sound like I'm being sarcastic - but that is such a horrible question to ask as it depends on what you want it to do and how deep your pocket is! I would always recommend separating the antenna from the base station equipment at a base station. You choose the type of antenna on what you want to achieve and checking the data sheets given by the supplier are validated. That pushes up the price as that means the aerials all need testing before they leave the factory. Or you do it.

But from then onwards there are so many criteria to take into account that I would find it difficult to answer that fully here because a) my lively hood depends on providing best practise advice to businesses that I can charge for (so why give everything away free here) and b) after 30 years in the business I am loathed to start writing an entire book on this forum on how to do RF installations properly, taking into account every possible eventuality and situation. Even if I did, I suspect that someone will cut a corner somewhere (as they don't understand the technical consequences of skimping on something that appears to them as being a tiny little detail of no importance) and as a result whatever they have built will fail to work as well as expected and who gets the blame for that? Me? No thanks. :-)
Same question - what is the best radio card for price performance,
bet you can guess the answer I want to give to that?! :-) But the Ubiquiti and Mikrotik cards are fine for what you pay for them. If you want even higher quality start looking for words like "carrier class".

To get best performance from a link or understanding the complexities of site sharing means understanding the risks of utilising unprotected spectrum, with very low cost equipment, yet expecting it to perform the same as links that cost tens of thousands. Understanding how to minimise antenna coupling, the usage of cavities where necessary, also when you'll need RF circulators and earthing everything correctly. Even knowing what types of equipment enclosures to use depending on the known extremes of the environment, the type of waterproofing tapes to use... the right type of CAT5, power and coax cables. Doing things the right way cost money. I have heard far too many people claim "why spend a hundred grand on a microwave link, I can do it for 100 bucks and get the same results!" Yeah, right.
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Re: Radio card RX bandwidth?

Wed Mar 23, 2011 1:03 am

You mean moving the antenna backwards and forwards horizontally? The other problem is the casing of that CPE is plastic.
Yes horiz movement - from your reply i would assume the case for the AP must perform two functions apart from the usual weatherproofing aspects (1) provide screening to reduce RF pickup from rear or all sides (2) to augment the antenna performance by acting as a "reflector element"
How long is the string and is it stretchable? OK, I know I sound like I'm being sarcastic - but that is such a horrible question to ask as it depends on what you want it to do and how deep your pocket is!
Aah no harm in asking :D
I would always recommend separating the antenna from the base station equipment at a base station

I have to date used intergrated antenna+board+radio card as the example listed, less interconnect cables used, regardless of quality as they can change the effective the rf load presented to the radio card, just calculating insertion loss for connectors and cable length can be misleading, can only reduce the TX power from a AP.

Once again thank you for your replies.
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Re: Radio card RX bandwidth?

Wed Mar 23, 2011 1:31 am

from your reply i would assume the case for the AP must perform two functions apart from the usual weatherproofing aspects (1) provide screening to reduce RF pickup from rear or all sides (2) to augment the antenna performance by acting as a "reflector element"
1 yes, 2 no. The antenna is placed in the front lid and the back of the antenna has a steel plate behind it as ground plane / reflector. It also reduces RF getting back into the electronics. But as it is only a plate, and not a box, it is not a faraday cage. Therefore it offers no screening effect. The reason why those boxes have no screening is because they are low cost and they expect you, as the purchaser, to understand it's correct application! (In one situation where a client did not wish to utilise a different type of box, we advised spraying the inside of their Mikrotik Outdoor case with Nickel RF Screening spray paint and this was very effective at reducing interference).

Placing multiple CPE boxes of that size on one mast begins to also look unsightly. I hope your neighbours don't care! :-)
less interconnect cables used, regardless of quality as they can change the effective the rf load presented to the radio card, just calculating insertion loss for connectors and cable length can be misleading, can only reduce the TX power from a AP.
Putting the enclosures a metre or two away from the antennae reduces RF getting into them. Using metal boxes, further reduces the chances of you getting interference from other sources and you causing interference to them. 1m of very low loss coax will only drop the signal by about 2dB approx, but the benefits of getting a much lower noise floor and less interference more than make up for the small signal loss. Anyway, by using better antennae with gain figures which are the same in reality as on paper can make up for that loss too. :-)
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Re: Radio card RX bandwidth?

Wed Mar 23, 2011 1:35 pm

1m of very low loss coax will only drop the signal by about 2dB approx
Yes but with reference to a PTP link that loss is doubled to 4db, a quick calculation using XR5 card is @54 is 23dbm = 631mw, 4 db reduction = 19dbm = 80mw
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Re: Radio card RX bandwidth?

Wed Mar 23, 2011 9:08 pm

If you have a badly engineered system where you are getting 20-30dB of interference, the link keeps failing or you have a low throughput, but then you install it correctly with a 4dB loss, but the removal of that 20-30 dB of interference, are you still trying to argue that gaining the 4dB is more important than the loss of that interference?

Also, if you can't afford to lose 4dB on a link, without it falling over, you need to re-assess your link budget! Any link with less than 20dB of fade margin is asking for trouble. Yes, you can make them work with figures of between 10dB and 20dB, but they will not be as reliable and there will always be the risk of it failing more often. If your fade margin is only 4dB, then you already have an even more serious problem than worrying about losing 4dB in cable losses. :-)
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Re: Radio card RX bandwidth?

Thu Mar 24, 2011 12:48 pm

If you have a badly engineered system where you are getting 20-30dB of interference, the link keeps failing or you have a low throughput, but then you install it correctly with a 4dB loss, but the removal of that 20-30 dB of interference, are you still trying to argue that gaining the 4dB is more important than the loss of that interference?
No - i have for example a 20.5Km ptp link which has a fade margin of 29dB, my policy is simple - don't insert any item in the broadcast/receive chain unless absolutely necessary, i take all of your points and thank you very much for taking the time and the effort in the detail of your replies,
..we advised spraying the inside of their Mikrotik Outdoor case with Nickel RF Screening spray paint and this was very effective at reducing interference).
Good suggestion but i would be concerned that paint onto plastic will crack and break when the AP is vibrating in high winds on a exposed location, maybe silver foil stuck onto the inside of the plastic case and once again because of a wavelength of 5.172cms i don't want to solve one problem and generate another?

All of this effort and research is into why just one AP on this tower has regular disconnects/reconnects when using NV2 but OK on 802.11 and the other AP's are OK using NV2, I have tried tweaking this AP in the advanced setting tab?
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Re: Radio card RX bandwidth?

Thu Mar 24, 2011 9:52 pm

a 20.5Km ptp link which has a fade margin of 29dB
The only way I can make a 20.5km link on 5.8GHz give me a 29dB margin is if the EiRP is 50dBm! (i.e. 100 Watts) Am I assuming this is your method of removing all obstructions or losses - like birds - you fry them out of the way? :lol:
(XR5 at 28dBm, 1dB pigtail&connector loss, 23dBi antenna gain = +50dBm EiRP then -134dB Path Loss, 23dB Antenna gain, 1dB pigtail&connector loss, assuming 12MBps connection rate, -91dBm Receiver sensitivity required = 29dB SNR)
silver foil stuck onto the inside of the plastic case and once again because of a wavelength of 5.172cms i don't want to solve one problem and generate another?
Tried aluminium foil once a long time ago but had some many practical problems trying to make it fit the shape of the box without one single little break in the foil (which then breaks it's effectiveness) - so that's why I now only use the paint. It works VERY effectively. It covers every single tiny little corner or bend thus ensuring a complete unbroken surface and provides a hard covering once dry. I have never seen it crack with use. I have seen boxes I've done years ago and they are still intact. But overall, you are still better off using a metal box, a short length of coax and a decent aerial in the first place! :-)
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Re: Radio card RX bandwidth?

Fri Mar 25, 2011 1:52 am

silver foil stuck onto the inside of the plastic case and once again because of a wavelength of 5.172cms i don't want to solve one problem and generate another?
Tried aluminium foil once a long time ago but had some many practical problems trying to make it fit the shape of the box without one single little break in the foil (which then breaks it's effectiveness) - so that's why I now only use the paint. It works VERY effectively. It covers every single tiny little corner or bend thus ensuring a complete unbroken surface and provides a hard covering once dry. I have never seen it crack with use. I have seen boxes I've done years ago and they are still intact. But overall, you are still better off using a metal box, a short length of coax and a decent aerial in the first place! :-)
I remember to have red somewhere that to shield a box (make a cage of Faraday) you can use metal fly screen or metal chicken fence. As long as the raster has openings of less then 1/4th of the wavelength it will block most of the signal.
5Ghz comes down to 1cm in this case. So cracks in the alu foil smaller shouldn't make such a difference.

I have a whole series of MT big outdoor boxes that I would like to convert that way.

I have been googli'n for this paint. I can find special paint for electromagnetic wave shielding of houses etc. I was thinking: "a spray can of metallic car paint, would that not do the job?" I have been told the metallic effect is created by alu particles. That should than create a nice shield it I just spray that on the inside (or outside?) of the box?
Its available around the corner in every car shop or DIY.
The special paint is a bit harder to find and more expensive..

But what about reflection from the radio card in this now shielded box? If any signals leak outside the pigtails connector it will now be bounced back inside the box and start its own ´interfering´live?
 
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Re: Radio card RX bandwidth?

Fri Mar 25, 2011 11:49 am

he only way I can make a 20.5km link on 5.8GHz give me a 29dB margin is if the EiRP is 50dBm! (i.e. 100 Watts) Am I assuming this is your method of removing all obstructions or losses - like birds - you fry them out of the way? :lol:
I was trying to include as few "Bankers" in that beam :)
(XR5 at 28dBm, 1dB pigtail&connector loss, 23dBi antenna gain = +50dBm EiRP then -134dB Path Loss, 23dB Antenna gain, 1dB pigtail&connector loss, assuming 12MBps connection rate, -91dBm Receiver sensitivity required = 29dB SNR)
I use http://www.ligowave.com/linkcalc/ XR5 23dbm @54Mhz, grid 24dbi, cable loss 2db, -91dbm (had-94?) = 27db fade margin and +47dbm
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Re: Radio card RX bandwidth?

Mon Apr 04, 2011 5:08 pm

If we dismiss the possibilities of RouterOS being the potential issue, and only consider the RF portion of this site, there are a few other items that could be considered.

Can you provide a material list for your site? i.e., enclosures, exact feed line particulars, connector types, and physical site information.

We have the antenna. Now let's consider that you may have coupling, IM, or other possibilities. From earlier, additional shielding is being considered, so let's dive into your situation.
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Re: Radio card RX bandwidth?

Tue Apr 05, 2011 1:56 am

If we dismiss the possibilities of RouterOS being the potential issue, and only consider the RF portion of this site, there are a few other items that could be considered.

Can you provide a material list for your site? i.e., enclosures, exact feed line particulars, connector types, and physical site information.

We have the antenna. Now let's consider that you may have coupling, IM, or other possibilities. From earlier, additional shielding is being considered, so let's dive into your situation.


My question is - should i be concerned at signal levels from other AP's on the mast at these levels when using 5320?
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Re: Radio card RX bandwidth?

Tue Apr 19, 2011 11:06 pm

To refresh the details.... each antenna has an enclosure containing only one radio correct?

If you are seeing a -24 from a separate radio, on the radio in question, then yes, you have excessive interference. To quantify how much this is affecting you (without an analyzer,) turn that radio off and see if your situation improves.

A more complex test scenario would be to determine the levels of unwanted emissions at the antenna connector in question, and then analyze what the theoretical impact would be to your radio. i.e., some radios have sufficient on board filtering to eliminate signals such as the -24 you are seeing. However, what we must consider is that for the receiver to see this level near your desired frequency, that you may be suffering interference radio to radio, without feed line or antenna assistance. This is what has been mentioned in the previous posts.

Ubiquiti radios tend to suffer receiver damage when levels rise into the 20's. We try to avoid anything stronger than -35, which is where we start to see excessive degradation to performance. Even on isolated PtP links, signal levels greater than -35 can cause significant issues.
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Re: Radio card RX bandwidth?

Wed Apr 20, 2011 12:16 am

After a nice trip in radio transmitting and receiving technology I come back to the very first question by n21roadie;

He runs a scan and ´sees´ all these other radio's with relative strong signals.
Now his question was if this then would mean in normal ´working´ (=receive-send-receive-send-receive etc. etc.) condition the receiver would be harmed by these ´foreign´ signals.

Imho running a scan the software opens the BAW filter for all frequencies in the chosen band.
So now the receiver (that is only receiving continuously now anyway) receives all signals in that chosen band it can ´hear´.
If you for instance set one frequency in the ´scan list´ under normal wireless interface config than the scan tool also only shows ´foreign´ (because he is NOT sending now) signals in that same frequency.
Now this can also be that the software is just not showing all the others but I would hope it to be that the receiver's BAW filter is limited to let that single chosen frequency through only....

Under normal working condition the same BAW filter should guard against any interferences from frequencies outside its own working frequency, up to certain level off course.

This is a very simplistic answer to that initial question which would probably satisfy most ´day to day´ users on this forum. But we would have missed a lot of interesting info if this would have been given as an answer straight away!

And by the way; I started spray painting the insides of every plastic box that comes under my hands. AP's but even CPE's. In dense used spectrum (nest: 5Ghz band! :) ) my CPE's did suffer from other ISP's working in near same channels and after the spray-can use the results are promising! I did a test on my desk and found a drop of 3 to 7dBm of signal on a radio connector on a card in a plastic box scanning for an antenna 2 mtrs away for that box's back.
I tried at least 5 boxes and sometimes the difference was 3, some other showed 7dBm improvement!
Which paint I used? Ordinary sink paint. Every metal workshop working with galvanised steel uses it... € 2,50 a bottle that does do me 6-8 boxes. Each with 2 layers! (And don't forget to fit a little earth wire between the lid and the box.)
Considering the price, I am probably going to spray the boxes on the outside as well... It even looks better and as a bonus the silvery shining layer reflects more sunlight so the boxes stay cooler! :D
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Re: Radio card RX bandwidth?

Wed Apr 20, 2011 3:11 am

Hi ...

Nice topic.

About the receiver BB filter, there is a pix from a chipset manufacturer.

Image

I think when bandscan runs they simply keep the filter at the selected channel BW and jump the local oscilator frequency, waiting some miliseconds on each frequency, time enough to sniff signal levels, noise levels, etc.

About the AP freq scan picture, there's a lot of power hitting this AP.

If we round the levels detected at 5865 & 5700 to -33, both toghether means -30dBm. And the -24dBm one. Too much for certain cards. From this excess power came intermod, lna desense (blocking), etc.

I guess there's no card able to filter a single 20MHz channel on its front-end but only at baseband. A narrow filter like that must be external, interdigital > 7 poles or any other waveguide technology such as iris, etc.

I'm facing some 900MHz issue, and the best tool (or toy lol) I found at MT devices was not the standard quality parameters such as CCQ, noise floor & etc - but - under \interface wireless monitor, runing it, with the daptive noise enabled ... there is a monitored parameter called current-ofdm-error.

Since I started selecting frequencies based on the lowest ofdm-error, link drops reduced a lot, troughput more stable than before & etc.

I have a 2.4AP with a XR9 on a 411AR. 2.4AP was messing up XR9 when tunned to 2422 (XR9 at 2437 = 917MHz). At this time, CCQ was > 80, noise floor -95, S/N 20dB, but several unexplained disconections. The 900MHz ofdm-error was varying from 100 to 300.

When I changed 2.4AP to 2412, 900MHz ofdm-errors dropped to 1 ... 3. And from one link drop each 3 ... 5 minutes now it lasts connected for 5 ... 10 hours (nlos links btw).

My next step is finish a 7 pole interdigital filter for 915 ... 928 to install at one client where there is a 870MHz cell phone harness nearby. There, the ofdm-error is > 700, peaking 3000 at the rush hours.

For now to select "good frequencies" I'm using this parameter, measured at AP (pmp scenarios), even when freq usage or band scan tools shows me the opposite.

Regards
Marcus Ramos
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(Microwave HW, RF, antennas, propagation)
S.Paulo - Brazil
 
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Re: Radio card RX bandwidth?

Thu Apr 21, 2011 2:26 am

Hi ...

Nice topic.

About the receiver BB filter, there is a pix from a chipset manufacturer.

Image

I think when bandscan runs they simply keep the filter at the selected channel BW and jump the local oscilator frequency, waiting some miliseconds on each frequency, time enough to sniff signal levels, noise levels, etc.

About the AP freq scan picture, there's a lot of power hitting this AP.

If we round the levels detected at 5865 & 5700 to -33, both toghether means -30dBm. And the -24dBm one. Too much for certain cards. From this excess power came intermod, lna desense (blocking), etc.

I guess there's no card able to filter a single 20MHz channel on its front-end but only at baseband. A narrow filter like that must be external, interdigital > 7 poles or any other waveguide technology such as iris, etc.

I'm facing some 900MHz issue, and the best tool (or toy lol) I found at MT devices was not the standard quality parameters such as CCQ, noise floor & etc - but - under \interface wireless monitor, runing it, with the daptive noise enabled ... there is a monitored parameter called current-ofdm-error.

Since I started selecting frequencies based on the lowest ofdm-error, link drops reduced a lot, troughput more stable than before & etc.

I have a 2.4AP with a XR9 on a 411AR. 2.4AP was messing up XR9 when tunned to 2422 (XR9 at 2437 = 917MHz). At this time, CCQ was > 80, noise floor -95, S/N 20dB, but several unexplained disconections. The 900MHz ofdm-error was varying from 100 to 300.

When I changed 2.4AP to 2412, 900MHz ofdm-errors dropped to 1 ... 3. And from one link drop each 3 ... 5 minutes now it lasts connected for 5 ... 10 hours (nlos links btw).

My next step is finish a 7 pole interdigital filter for 915 ... 928 to install at one client where there is a 870MHz cell phone harness nearby. There, the ofdm-error is > 700, peaking 3000 at the rush hours.

For now to select "good frequencies" I'm using this parameter, measured at AP (pmp scenarios), even when freq usage or band scan tools shows me the opposite.

Regards
Hi Marcus,

Yes, the topic is very interesting. I hope to learn a lot from you, and with me hopefully lots of others.
But you are obviously more into the subject than lots of us. I am afraid I am losing you a bit here and there, so some explanations again please:

The graph you showed us, what does it tell? The only axe I understand is the dB. But I see 4 different graphs. What are the variables? And what is the horizontal axe telling me?
The title also brings not a lot of clarification. "Frequency response" (I can understand) versus "Coarse setting" (And a ´fine stetting of 010?). What do they mean with all this?

Then your 900Mhz issue. You write "(XR9 at 2437 = 917Mhz)"? What is that. In my simple understanding 2437 means 2437Mhz. Where is this 917Mhz coming from? Does is has any relation with 2,4Ghz band?

Your "7 pole interdigital filter for 915 ... 928"?
"7 pole"? Pole in "polarity"? How do I see that?
"interdigital"? What is that? Is this a digital filter?
"915...928"? Is this freq. in Mhz? This has relation to the 917Mhz mentioned earlier?

You tell us about the ofdm-error listing in wireless monitor.
Than you tell us you are going to use this to select for ´good frequencies´ by measuring in the AP.
But I can only find the ofdm-error listing in the wireless monitor of the client?
In the unit running AP such option is not listed.

So basically I can only run the monitor on station when it is associated and than read the ofdm-error parameter.
If I now want to test all other channels I first have to swap AP to another channel, and make the station follows and I can do the monitor again...
Due the ´real´ readings we need this means the monitor also has to be performed on the actually ´live´ network in which case if we talk about an AP with several clients associated these customers are not going to be happy with all the disconnects because AP changes channel every time .....
Do you really use this method to find best channel?

Sorry for all these questions. But I need full understanding to really get an hold on all the ins and outs of this subject.
See it as the pupil asking the master.. :D
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Re: Radio card RX bandwidth?

Thu Apr 21, 2011 4:40 am

Hi ...
The graph you showed us, what does it tell? The only axe I understand is the dB. But I see 4 different graphs. What are the variables? And what is the horizontal axe telling me?
I think this graph created more confusion than clear things up but is somewhat simple.

It shows the frequency response of the "intermediate frequency" of a receiver, in this case not intermediate because this receiver is called "zero-intermediate-frequency". This is the architeture most used today to build 802.11 radios (and several ptp ones).

By some math approach it's possible to transform any RF signal in two components, 90º phase difference between them. The result, if we use a 20MHz 802.11G mode, is two signals that fill the spectrum from DC to 10MHz, 90º appart.

This means that at those receiver architetures, to have a 20MHz channel we need to have 10MHz BB filters (twice).

Don't worry about variables nor numbers (0,1 01, etc). This was only the notation specific for a binary code that "program" this filter inside this specific chipset. Vary from manufacturer to manufacturer.

I just want to show - more or less - how gentle are the skirt of such filters.

There is 4 sample curves, the left one has zero db loss until ~7MHz (so a 14MHz channel), the second one ~10MHz (20MHz channel), ~15MHz (30MHz channel) and the last ~18MHz (36MHz channel).

From this graph & 10MHz wide filter (20MHz channel), the "adjacent" channel center frequency is atenuated by 45dB. But the lower frequencies of this adjacent channel will be attenuated much less (lets say 20 to 30dB). This drive us to set 2 frequencies at least leaving one blank 20MHz channel (needs to look at a table to avoid overlapping) to have > 45dB nearby frequencies rejection.

But - this numbers are valid after the 5GHz signal was "downconverted" to DC ... 20MHz. So the first stage at the receiver will see everything from 5.1 to 5.9GHz. No narrow band filtering there, only a small etched filter on printed circuit boards or a ceramic filter (or none, depends on the design of the card). This means that strong signals from other rigs at 5GHz may not be visible at baseband (they was filtered there) but can overload the receiver first stages, generating intermodulation, desense, blocking, etc. This can be "detected" as phantom signals, noise floor elevation, desired signal level reduction, etc.
Then your 900Mhz issue. You write "(XR9 at 2437 = 917Mhz)"? What is that. In my simple understanding 2437 means 2437Mhz. Where is this 917Mhz coming from? Does is has any relation with 2,4Ghz band?
Ah, this is the way MT (and other drivers) set XR9 frequencies. XR9 & SR9 uses a 2.4GHz chipset and convert this frequency down to 900MHz band. For SR9 the frequency is already displayed as 917, 922 etc on MT ROS. But XR9 still displaying 2.4GHz ones so we need to use a table to figure which 900MHz frequency we're on. With this cards came an adhesive tape named XR9 Frequency Chart where UBNT relate 802.11 channel to 902 ... 928MHz band.

So this means a 900MHz card is a potential source of interference at 2.GHz and vice versa, at least if both cards share the same board PCI adaptors.
Your "7 pole interdigital filter for 915 ... 928"?
"7 pole"? Pole in "polarity"? How do I see that?
"interdigital"? What is that? Is this a digital filter?
"915...928"? Is this freq. in Mhz? This has relation to the 917Mhz mentioned earlier?
Interdigital is a kind of microwave filter, where inside a "waveguide" there is some metal rods that measure ~1/4 wavelenght at the desired frequency. 7 pole is the number of "rods". This is not an accurate explanation, there's several techniques to build interdigital filters, in my case I choose air as dieletric. Later I post a draft of such filter. Is supose to be low loss on passband (~0,5dB) and more than 30dB loss at the first 2MHz outside the desired passband. The loss at 875MHz must be more than 60dB (calculated). And yes, the idea is cut away any out of band signal around this client (there is a cell phone tower ~300m distant and the antenna azimuth is 15º off it).

OFDM errors later ;-)

Regards;
Marcus Ramos
Electronics Technician
(Microwave HW, RF, antennas, propagation)
S.Paulo - Brazil
 
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Re: Radio card RX bandwidth?

Thu Apr 21, 2011 12:35 pm

To refresh the details.... each antenna has an enclosure containing only one radio correct?
Yes only one radio card - 433AH +XR5
If you are seeing a -24 from a separate radio, on the radio in question, then yes, you have excessive interference. To quantify how much this is affecting you (without an analyzer,) turn that radio off and see if your situation improves.
I don't have at present any issues using NV2 but as the demand for extra bandwidth on the AP's increases this could change,

Originally my question was part of a fault finding elimination process to solve just why one AP's running NV2 had hourly disconnects reconnects but a firmware upgrade of the 433ah solved this?

But thanks to replies, a lot of good information has been posted and could be labelled in my opinion as "Best Practice"
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Re: Radio card RX bandwidth?

Thu Apr 21, 2011 2:40 pm

Then your 900Mhz issue. You write "(XR9 at 2437 = 917Mhz)"? What is that. In my simple understanding 2437 means 2437Mhz. Where is this 917Mhz coming from? Does is has any relation with 2,4Ghz band?
Ah, this is the way MT (and other drivers) set XR9 frequencies. XR9 & SR9 uses a 2.4GHz chipset and convert this frequency down to 900MHz band. For SR9 the frequency is already displayed as 917, 922 etc on MT ROS. But XR9 still displaying 2.4GHz ones so we need to use a table to figure which 900MHz frequency we're on. With this cards came an adhesive tape named XR9 Frequency Chart where UBNT relate 802.11 channel to 902 ... 928MHz band.

So this means a 900MHz card is a potential source of interference at 2.GHz and vice versa, at least if both cards share the same board PCI adaptors.
OK, that clear to me. I never knew this but I understand the extra interference issue the basic 2.4Ghz chipset can cause on 900Mhz and vice versa. I don't use both so to me it is not an issue but interesting info. thnks.
Your "7 pole interdigital filter for 915 ... 928"?
"7 pole"? Pole in "polarity"? How do I see that?
"interdigital"? What is that? Is this a digital filter?
"915...928"? Is this freq. in Mhz? This has relation to the 917Mhz mentioned earlier?
Interdigital is a kind of microwave filter, where inside a "waveguide" there is some metal rods that measure ~1/4 wavelenght at the desired frequency. 7 pole is the number of "rods". This is not an accurate explanation, there's several techniques to build interdigital filters, in my case I choose air as dieletric. Later I post a draft of such filter. Is supose to be low loss on passband (~0,5dB) and more than 30dB loss at the first 2MHz outside the desired passband. The loss at 875MHz must be more than 60dB (calculated). And yes, the idea is cut away any out of band signal around this client (there is a cell phone tower ~300m distant and the antenna azimuth is 15º off it).
That's clear now too.
OFDM errors later ;-)
I'm eagerly awaiting your comments... :)

Your first explanation, regarding the graph, needs a bit more ´chewing´ from my end. We'll come back on that one later....
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Re: Radio card RX bandwidth?

Fri Apr 22, 2011 5:25 am

Hi Rudy et al:

Look, I'm a self thought person, not a pro :D.

I found this current-ofdm-error by accident and some days later MT support guys explained it.

I was doing some tests with a script. My need was: change the actual 900MHz AP frequency (917 or 922MHz, 5MHz channel) as soon as the number of authenticated clients was less than 2 (one ap and 2 nlos clients). There was certain hours of the day where one specific client (those which is close to a cell phone tower) disconnects may be twice a minute. Sometimes seems that this client reception was blinded by some interference.

Anyway, this script was a temporary solution, until I have time & way to build a filter, just guessing the reason was out of band intereference. Meantime I ordered a UBNT AirView900-EXT (a 900MHz USB spectrum analyzer) to monitor this site.

Every time this successive disconects starts was enough switch to the other frequency and things calm down. Calm down means: instead of 2 disconections per minute, became 1 disconection each 10 ... 20min (each lasts a fraction of a second anyway but ...).

So to recover the number of auth clients on the fly, instead of use SNMP info (which will require the use of a remote Dude sever & etc), I used part of a script I did to switch the time source for ROS NTP Server between GPS (master) or a www NTP Server. On this script I used some path to \system gps monitor and from there I read the GPS status (valid or not).

I used the same aproach to \interface wireless monitor (int number) and there was a lot of information, some of them avialable via Winbox reg table such as signals, ccq, ptroughput, etc. And, aditionally, there was current-cck-errors & current-ofdm-errors.

Well, "ofdm error" measurement should be something very "hardware" related, I mean, certain parameters that exists before any error correction introduced by the chipset itself or by the drivers (depends on the architeture I guess). May be even the amout of "stress" some demodulator at the chipset suffers to keep received signals within certain standard pattern mask.

Short story, common sense told me that any error must be kept as low as possible. May be the measured "200 ... 300" was low. But when I started changing 2.4AP frequency (a RB411AR), the error at 900MHz card dropped from 200 ... 300 to 1 ... 5.

Since then, those disconnections stoped, e.g. from one each 15min to one each 6 or more hours.

Note that CCQ was "high" (ccq>80) both cases (error ~300 or error ~5)

To see this info: (terminal)\wireless interface monitor (interface number). On advanced winbox tab or via terminal be sure that adaptive noise imunity is enabled. As MT support guys explained me, this error measurement depends of such hw resource.

Image

Depending on the avialable info on terminal, the window size hide it. So press the space bar to "scroll" the info on the terminal window.

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Re: Radio card RX bandwidth?

Fri Apr 22, 2011 4:26 pm

Hi ......................



By some math approach it's possible to transform any RF signal in two components, 90º phase difference between them. The result, if we use a 20MHz 802.11G mode, is two signals that fill the spectrum from DC to 10MHz, 90º appart.

This means that at those receiver architetures, to have a 20MHz channel we need to have 10MHz BB filters (twice).

Don't worry about variables nor numbers (0,1 01, etc). This was only the notation specific for a binary code that "program" this filter inside this specific chipset. Vary from manufacturer to manufacturer.

I just want to show - more or less - how gentle are the skirt of such filters.

There is 4 sample curves, the left one has zero db loss until ~7MHz (so a 14MHz channel), the second one ~10MHz (20MHz channel), ~15MHz (30MHz channel) and the last ~18MHz (36MHz channel).

From this graph & 10MHz wide filter (20MHz channel), the "adjacent" channel center frequency is atenuated by 45dB. But the lower frequencies of this adjacent channel will be attenuated much less (lets say 20 to 30dB). This drive us to set 2 frequencies at least leaving one blank 20MHz channel (needs to look at a table to avoid overlapping) to have > 45dB nearby frequencies rejection.

But - this numbers are valid after the 5GHz signal was "downconverted" to DC ... 20MHz. So the first stage at the receiver will see everything from 5.1 to 5.9GHz. No narrow band filtering there, only a small etched filter on printed circuit boards or a ceramic filter (or none, depends on the design of the card). This means that strong signals from other rigs at 5GHz may not be visible at baseband (they was filtered there) but can overload the receiver first stages, generating intermodulation, desense, blocking, etc. This can be "detected" as phantom signals, noise floor elevation, desired signal level reduction, etc.

...........................

Regards;
...So the first stage at the receiver will see everything from 5.1 to 5.9GHz.
So overload of the receiver first stages can occur with high signals from other AP's on the mast?

From the graph if other AP's were 60Mhz apart then the attenuation by this filter is -90db but if the first stages are already overloaded then this would tell me a reduction of high signal levels from other AP's on the mast is a must.
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Re: Radio card RX bandwidth?

Fri Apr 22, 2011 5:38 pm

...So the first stage at the receiver will see everything from 5.1 to 5.9GHz.
So overload of the receiver first stages can occur with high signals from other AP's on the mast?

From the graph if other AP's were 60Mhz apart then the attenuation by this filter is -90db but if the first stages are already overloaded then this would tell me a reduction of high signal levels from other AP's on the mast is a must.
That's it.

Depends on the receiver chipset caracteristics anyway. Looking at some numbers from a sample manufacturer, they say that 1dB compression point at the rx rf pre-amp can vary from -35dBm if the gain is 60dB to +14dBm if the gain is 30dB.

I mean ... 60dB gain will be automatically used if the desired signal is low. This gains can be "distributed" on such chipsets, where designer can try to reduce first stage gain & increase "after filter" gain. The penalty is that reducing first stage gain the system noise figure increase.

After this input low noise amplifiers there is a mixer. Another source of concern. You increase the desired signal - and - the undesired with the pre-amp. A standard mixer will use +7dBm from an oscilator. The max recomended RF signal is -20dBm. May be the reason why most cards specs are -30dBm max signal at input.

Unfortunatelly we don't have how to "trim" such gains, something like two different profiles like "clean site" & "crowded site".

So in a crowded tower the "solution" is a single channel bandpass filter, I don't know even if this kind of filter exists as of-the-shelf. This should be ok "today", but if you need to change frequency for any reason this piece of hardware will became useless.

Your -14dBm signal ... try to switch its antenna polarity.

Image

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Re: Radio card RX bandwidth?

Fri Apr 22, 2011 6:45 pm

So in a crowded tower the "solution" is a single channel bandpass filter, I don't know even if this kind of filter exists as of-the-shelf. This should be ok "today", but if you need to change frequency for any reason this piece of hardware will became useless
Maybe i should try some sort of physical barrier between each AP to reduce the strong signals (like -24dbm) and even to reduce to say -40dbm from -24dbm should make a big difference to first stage overload, I mentioned in another post about using a earthed wire mesh grid to reduce these signals, another option i have is to horizonally rotate each AP as there are mounted on 500mm offsets from the mast for reduction of strongest signal from side lobes of other AP.

Syncing the AP's will probally solve a lot of this (or not if the rx is overloaded) and also while AP's can be synced how about the PTP links?
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Re: Radio card RX bandwidth?

Fri Apr 22, 2011 7:41 pm

Maybe i should try some sort of physical barrier between each AP to reduce the strong signals (like -24dbm) and even to reduce to say -40dbm from -24dbm should make a big difference to first stage overload, I mentioned in another post about using a earthed wire mesh grid to reduce these signals, another option i have is to horizonally rotate each AP as there are mounted on 500mm offsets from the mast for reduction of strongest signal from side lobes of other AP.
Yes, going from -24 to -40 will make a big difference. Assuming that the input power limit on such card is ... -30dBm ... to reach this value you'll need 8 (eight) -40dbm signals at the rx input and still 1 extra dB to hit the -30dBm limit.

One quick test is drop the -24dBm link for a while to see what will be the performance of the remaining links.

Does you have room to decrease the power of such AP? I mean, if the power is 24dBm, drop it to 10dBm.

Some grid barrier can work as well or even slightly move up or down the -24dBm source to take advantage of the antenna null patterns.

Syncing the AP's will probally solve a lot of this (or not if the rx is overloaded) and also while AP's can be synced how about the PTP links?
I guess it should solve it all - if - the tx & rx cycles could be synched to some time slot (like NV2, tdma, etc).

I didn't read all posts but if you have lets say 4 or 5 APs at the same place (all yours) ... and only one is suffering with this -24dBm signal ... and you use 802.11A+Nstreme ... keep the antennas as is ... kill the -24dBm AP, add a "N" card at the interfered ... make-it accept connection of the -24dBm client (so moving from PTP to PMP with only 2 clients, one antenna at chain 0, another at chain 1, both enabled for tx & rx). N cards on legacy modes with both chains selected will use the strongest signal for/from each client. ;-)

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Re: Radio card RX bandwidth?

Sat Apr 23, 2011 2:40 am

One quick test is drop the -24dBm link for a while to see what will be the performance of the remaining links.

Does you have room to decrease the power of such AP? I mean, if the power is 24dBm, drop it to 10dBm.

Some grid barrier can work as well or even slightly move up or down the -24dBm source to take advantage of the antenna null patterns.
All of the AP's on this mast are working OK - thanks to NV2 but after doing a scan on all of the 5 ap's, 3 have lowest at -20+db, 1 has -30 as lowest but then 1 AP has an unbelievable -11db, the attached picture says it all.
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Re: Radio card RX bandwidth?

Sat Apr 23, 2011 3:38 pm

Hi ...

Taking this levels ... are they stable?

I mean, the -11dBm ... mesurement is stable or erratic? I mean durying a 1 minute sample period this measured value change, drops in this case ... from -11 to any another value, -20, -25 whatever but -11 most of the time?

Did you already disconected the pigtail from antenna (the one that pick this -11dBm) and terminate it with a 50ohm load?

I bet you already went trhu all those basic check up like pigtails failure, etc to figure where this huge signal is coming from, e.g. antenna itself, common mode path, etc. Just asking.

Yesterday I found an old bandpass filter, that was part of a Hirschmann UHF TV repeater. I have two of them, lying around for years at the garage, just to take surplus RF parts such as SMA cables, semi-rigid 50ohm coax, etc. One of this filters was tunned to UHF TV channel 45, another to channel 80 (855MHz). They was originally 6MHz wide with two "traps", one above the bandpass, another below. SMA both sides, went to the bench and re-tuned it to 915 ... 928MHz. Pretty flat, 1.5dB loss. And those traps that will be tunned on the field to kill out of band huge sources, such as cell phone signals, trunking, rfid, etc. Small enough to fit inside the RB433UAH case. Easter gift :-).

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Re: Radio card RX bandwidth?

Sat Apr 23, 2011 4:26 pm

Taking this levels ... are they stable?

I mean, the -11dBm ... mesurement is stable or erratic? I mean durying a 1 minute sample period this measured value change, drops in this case ... from -11 to any another value, -20, -25 whatever but -11 most of the time?
Over 1 min scan duration the -11 went to -12 and -10?
I bet you already went trhu all those basic check up like pigtails failure, etc to figure where this huge signal is coming from, e.g. antenna itself, common mode path, etc. Just asking.
It's coming off another sector AP on the mast 5865

Maybe time to spray the inside of these plastic AP box's and especially the sides+top+bottom+back panel but of course not the front panel with conductive paint for shielding, will remove AP housing but leaving mounting bracket in place, re-attach do scan again knowing that the AP is exactly in same position before removing otherwise results could be misleading.
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Re: Radio card RX bandwidth?

Sat Apr 30, 2011 9:14 pm

Over 1 min scan duration the -11 went to -12 and -10?
Yes. But seems ok. My mistake, once I had some RSL floating instantly almost 15 ... 20dB due to interference. But the cause was a 802.11B AP. You're running A mode.

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Re: Radio card RX bandwidth?

Sun Jun 05, 2011 8:07 pm

The mast with the high rx signals was working very good with NV2 (5 Ap’s + 2 PTP’s) but attached extra 2 PTP’s and like some tipping point was reached and 2 AP’s had hourly disconnects and one had every 4 or so hours disconnects, only one with the narrowest TX/RX (10°) beam did not suffer, the rest have 90°rx/tx beam

After trying 4.16, 4.17, and finally 5.4 i came to the conclusion that it must be caused by wireless protocol NV2 and it's lack of tolerance to other NV2 (high) signals?

For me a temp solution was to use a rotation of wireless protocols AP1 =802.11, AP2 =NV2, AP3 =802.11, etc
And for my issues I am going to concentrate on the reduction of unwanted signal levels to -30 or more ?
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Re: Radio card RX bandwidth?

Mon Jun 06, 2011 2:08 pm

.............................................................

And by the way; I started spray painting the insides of every plastic box that comes under my hands. AP's but even CPE's. In dense used spectrum (nest: 5Ghz band! :) ) my CPE's did suffer from other ISP's working in near same channels and after the spray-can use the results are promising! I did a test on my desk and found a drop of 3 to 7dBm of signal on a radio connector on a card in a plastic box scanning for an antenna 2 mtrs away for that box's back.
I tried at least 5 boxes and sometimes the difference was 3, some other showed 7dBm improvement!
Which paint I used? Ordinary sink paint. Every metal workshop working with galvanised steel uses it... € 2,50 a bottle that does do me 6-8 boxes. Each with 2 layers! (And don't forget to fit a little earth wire between the lid and the box.)
Considering the price, I am probably going to spray the boxes on the outside as well... It even looks better and as a bonus the silvery shining layer reflects more sunlight so the boxes stay cooler! :D
Rudy can you give me the brand of sink paint did you use and is it conductive for earthing?
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Re: Radio card RX bandwidth?

Tue Jun 07, 2011 1:25 am

.............................................................

And by the way; I started spray painting the insides of every plastic box that comes under my hands. AP's but even CPE's. In dense used spectrum (nest: 5Ghz band! :) ) my CPE's did suffer from other ISP's working in near same channels and after the spray-can use the results are promising! I did a test on my desk and found a drop of 3 to 7dBm of signal on a radio connector on a card in a plastic box scanning for an antenna 2 mtrs away for that box's back.
I tried at least 5 boxes and sometimes the difference was 3, some other showed 7dBm improvement!
Which paint I used? Ordinary sink paint. Every metal workshop working with galvanised steel uses it... € 2,50 a bottle that does do me 6-8 boxes. Each with 2 layers! (And don't forget to fit a little earth wire between the lid and the box.)
Considering the price, I am probably going to spray the boxes on the outside as well... It even looks better and as a bonus the silvery shining layer reflects more sunlight so the boxes stay cooler! :D
Rudy can you give me the brand of sink paint did you use and is it conductive for earthing?
Well, it is very ordinary spray paint. In fact any ´metallic´ paint (like used on cars) will do. As long as there are metal parts in it. The one I use is locally manufactured brand.
Show your appreciation of this post by giving me Karma! Thanks.

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Re: Radio card RX bandwidth?

Tue Jun 07, 2011 12:07 pm

Well, it is very ordinary spray paint. In fact any ´metallic´ paint (like used on cars) will do. As long as there are metal parts in it. The one I use is locally manufactured brand.
I tested a can of metallic spray paint from local auto store and it did not have any conductivity when checked with a multimeter, did a search and a aerosol (350ml) can of rf screening spray = €125 or for a 1ltr of Y screening paint = €133,
but before i start to work on the effected AP's, i have contacted the antenna manufacturers with pictures of antenna placement on the mast for their opinion on this issue.
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Re: Radio card RX bandwidth?

Sun Oct 09, 2011 7:36 pm

Update on using screening inside integrated AP has been a success no more NV2 disconnects (had tried OS updates alone but still disconnects) and strange just a drop of 4dbm from -11 to -15 after screening on just one of four AP's has made a difference, i will modify the rest currently using a combination of copper foil and Y-shield paint, I also increased the distance between the antenna pcb which is mounted onto the alumimum panel and front panel so the 20mm copper adhesive strip would be more effecting at shielding.

As these AP's were being used i wanted to ensure that this modification was conducted quickly and did not solve one problem but generate another so before i swapped the AP i did a screenshot of signal levels from clients and removed the AP box on the mast from the mounting brackett this to ensure when put back was exactly the same position before starting and also swapped over the original routerboard and radio card + pigtail, after the swap did a comparsion and all were the same so no reduction in signal area coverage which was concern before I started.

I noticed when painted the rear cover if tapped or vibrated carbon dust would come off the paint and being conductive this dust if lodged onto a component could cause failure so on hand i had some varnish to seal over the y-shield paint. Now I have a integrated AP with no link leads (LMR..Cables) and reduced losses so more power from AP.
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Re: Radio card RX bandwidth?

Fri Oct 14, 2011 4:21 pm

Further update on screening my sector AP's with just one done i had 4dm reduction (-11 to -15) just completed a second AP the reduction has gone down from -15 to -25 a 10db drop, so 14db since i started and 2 more to go it will be interesting to see what will be the final figure will be.

Has anybody seen effective screening done on a grid antenna dipole, I suppose a waveguide?
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Re: Radio card RX bandwidth?

Sat Oct 15, 2011 1:21 pm

n21roadie - I'm confused, which part of the antenna exactly do you suggest screening? Not sure you really are suggesting that part of an antenna is screened? :-)

As stated very early up in this thread, I recommend using an enclosure that is screened with metallic paint ( the proper nickel RF Screening paint not car paint) and of course, the screening must then in turn be earthed to the mast and again the mast must be earthed to the ground.

This race to produce cheap plastic boxes that are wide open to receiving and transmitting RF through every side (except where the antenna is obviously) is very disappointing to someone who has dealt with professional carrier class equipment for 25 years and now finds that whenever he is called in to sort out on-site interference for a client, he is presented with plastic boxes that are all radiating into each other's electronics! Well, no wonder they have a terrible problem :-(

As you are finding out, it is not until every single box is done, that you will see all this hard work being worthwhile.
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Re: Radio card RX bandwidth?

Sat Oct 15, 2011 7:04 pm

n21roadie - I'm confused, which part of the antenna exactly do you suggest screening? Not sure you really are suggesting that part of an antenna is screened? :-)

As stated very early up in this thread, I recommend using an enclosure that is screened with metallic paint ( the proper nickel RF Screening paint not car paint) and of course, the screening must then in turn be earthed to the mast and again the mast must be earthed to the ground.

..............................................

As you are finding out, it is not until every single box is done, that you will see all this hard work being worthwhile.
Nest the parts i screened on the antenna is the inside 20mm plastic lip that is surrounding the alumimum plate holding the antenna element with 20mm copper foil this is earthed back to routerboard, the back of the antenna as stated i used y-shield conductive paint but because carbon dust comes loose when tapped or vibrated I used a vanish seal over the conductive paint and this is also earthed back to the routerboard and multimeter has confirmed the earthing is good on the conductive paint, the alumimum panel which is attached to the front on the antenna I increased the internal distance back from the front this the provide better screening from the 20mm copper strip, at no stage is the front part of the antenna is screened just the inside sides+top/bottom around the antenna element and back only.
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Re: Radio card RX bandwidth?

Sat Oct 15, 2011 8:57 pm

the parts i screened on the antenna
When you refer to "antenna", you actually mean the enclosure the antenna sits inside - right?

You also asked about screening the feed to the dipole on a grid antenna. I haven't tried this, but my experience says this would make the antenna worse as you increasing the diameter of the central supporting structure housing the transmission line (usually coaxial) and introducing effects such as altered return loss performance, bandwidth change or even potential radiation pattern changes that may prove detrimental. I would leave the antenna alone.

Regarding paint - this is what I've used before http://uk.rs-online.com/web/p/emi-or-rf ... g/0568483/

Although copper based paint sprays are more effective than Nickel, I only used Nickel as that was what I already had in stock on the shelf from some other project. Using a spray paint, rather than one applied with a brush makes it easier to get an even, smooth layer of metal. But if it works - who cares what it looks like?! :-)

See also http://www.enthone.com/resources_detail ... ompcc.ascx

But be aware that you are trying to create a faraday cage. Leaving gaps or parts of the case that are still untreated will not complete the screening and render the effect much reduced. That is why it is always much better to separate the antenna from the case housing the RF components and placing the 'active' RF part in it's own screened box.

The best answer of course, is to use enclosures that are made from metal. There are also some excellent examples of low cost antennae that have a metal casing on the rear of the antenna (or even inside the rear of the antenna) that can take a Routerboard with short pigtails that go directly from the RB Wifi card to the rear antenna connector, thus reducing the leakage of RF out of the unit and conversely, RF from other antennae getting into the RF Cards and electronics. The ones to steer clear of are the ones that have a hole in the rear of the antenna to take a routerboard, but the rear of the antenna enclosure is just plastic with no shielding!
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Re: Radio card RX bandwidth?

Sat Oct 15, 2011 9:46 pm

the parts i screened on the antenna
When you refer to "antenna", you actually mean the enclosure the antenna sits inside - right?

You also asked about screening the feed to the dipole on a grid antenna. I haven't tried this, but my experience says this would make the antenna worse as you increasing the diameter of the central supporting structure housing the transmission line (usually coaxial) and introducing effects such as altered return loss performance, bandwidth change or even potential radiation pattern changes that may prove detrimental. I would leave the antenna alone.

Regarding paint - this is what I've used before http://uk.rs-online.com/web/p/emi-or-rf ... g/0568483/

Although copper based paint sprays are more effective than Nickel, I only used Nickel as that was what I already had in stock on the shelf from some other project. Using a spray paint, rather than one applied with a brush makes it easier to get an even, smooth layer of metal. But if it works - who cares what it looks like?! :-)

See also http://www.enthone.com/resources_detail ... ompcc.ascx

But be aware that you are trying to create a faraday cage. Leaving gaps or parts of the case that are still untreated will not complete the screening and render the effect much reduced. That is why it is always much better to separate the antenna from the case housing the RF components and placing the 'active' RF part in it's own screened box.

The best answer of course, is to use enclosures that are made from metal. There are also some excellent examples of low cost antennae that have a metal casing on the rear of the antenna (or even inside the rear of the antenna) that can take a Routerboard with short pigtails that go directly from the RB Wifi card to the rear antenna connector, thus reducing the leakage of RF out of the unit and conversely, RF from other antennae getting into the RF Cards and electronics. The ones to steer clear of are the ones that have a hole in the rear of the antenna to take a routerboard, but the rear of the antenna enclosure is just plastic with no shielding!
Enclosure - correct,

With painting the inside of the back of the enclosure which seats onto the front lip of the enclosure which has copper 20mm strip attached provides a complete shielding solution,

As regards screening the feed to the dipole on a grid antenna the only item i have seen so far is this design
http://www.sstua.com/index.php?p=products&item=55
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Re: Radio card RX bandwidth?

Sun Oct 16, 2011 12:02 am

Hi ...

Locally we have some manufacturers that handle nickel, cooper or silver compounds (e.g spray, resin, etc) that can be applied to PVC and several other isolating materials.

I'm ready to test another approach since I does not use any antenna intergrated with AP. I run common sector or grids connected to APs via LMR400 short runs.

As Nest says, is pretty strange find "rf rigs" inside plastic boxes while pro market hold them on metal enclosures.

In this case and to keep them waterproof ... I'm looking on the surplus market for some CATV aluminum enclosures. I remember some nice line extenders or even trunk amps enclosures from Scientific Atlanta, Magnavox et al that can easily be adapted to hold routerboards inside.

A 2 ... 4mm thick aluminum box than can have its normal 3/4" pin connector holes sealed by CATV stock parts build for that, with rubber gasket etc.

I have a 433UAH fitted with 2 x R52nM + XR9 and no "internal" problem at all. The 52nM are working on 2.4GHz (ch 1 & 13 @ 10MHz bw) and XR9 at 2442/2437 5 or 10 MHz wide. But things calm down after spreading some ferrite beads & clamps here and there (pigtails close to mini-pci cards, close to female N and at the UTP cables). This assembly still at a plastic enclosure. I'm cloning it ... but wants this clone inside one of those aluminum enclosures just to compare.

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Re: Radio card RX bandwidth?

Sun Oct 16, 2011 12:49 am

As regards screening the feed to the dipole on a grid antenna the only item i have seen so far is this design
That does not look to me to be a screened dipole. Nor does it appear to be screening the feed to the radiator. It looks more to me like a waveguide feed with horn antenna. I haven't seen this idea before on 'low cost' parabolic grid antennae. So, I think this is a different type of feed to what you were referring to, namely a coax cable going up the centre line up to a dipole radiator at the focal point. Sometimes the coax cable is replaced with a solid steel tube inside a tube to make the centre support more solid. But it's principle is a coaxial transmission line.

mramos - I have taken the white Mikrotik outdoor cases and sprayed them very successfully, I then use a 1m length of LMR400 up to the antenna above - in this way the antenna is not close to the electronics and the RF is fired away from the box. All about good design of an installation - something I learnt from other experienced colleagues over many years! How to do things properly :-)

It is disappointing that manufacturers of plastic enclosures do not do this screening at time of manufacture. :-( Instead one either gets a metal box (expensive / heavy) or an unprotected plastic box (cheap / light weight).

It is either that, or I have simply not found any good quality (but cheap) screened plastic enclosures.
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Re: Radio card RX bandwidth?

Sun Oct 16, 2011 3:50 pm

Hi ...

Horn is a nice way to feed antennas which have big f/d and where one dimension is bigger than the other, like the grid on the advertisement.

If a pannel is the way to go - in order to have some broad coverage - one resource to keep sidelobes and f/b ratio better than the standard designs is the use of some sort of "radome", e.g. something like the one at Nest avatar. A metal surface around the antenna edges, filled internally with rf absorber material.

It's a common procedure on microwave dishes where due to spillover and/or feeder inacuracies the sidelobes does not fit inside regulatory masks (or to be preventive if this dishes will exist in crowded towers).

I guess I saw at UBNT forum some time ago someone that sells some "kits" to antenna screening. Looks like aluminum "radomes" with different shapes, covered internally with rf absorber.

I have one site with two stock 17dBi sectors, 90º, back to back. Take a look how much signal are picked up by the "wrong" antenna. There I use a R52nM on legacy G mode (may be nstreme or nv2 if 3 CPEs are not UBNT's) with both chains enabled, one chain each antenna.

Image

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Re: Radio card RX bandwidth?

Sun Oct 16, 2011 5:21 pm

As regards screening the feed to the dipole on a grid antenna the only item i have seen so far is this design
That does not look to me to be a screened dipole. Nor does it appear to be screening the feed to the radiator. It looks more to me like a waveguide feed with horn antenna. I haven't seen this idea before on 'low cost' parabolic grid antennae. So, I think this is a different type of feed to what you were referring to, namely a coax cable going up the centre line up to a dipole radiator at the focal point. Sometimes the coax cable is replaced with a solid steel tube inside a tube to make the centre support more solid. But it's principle is a coaxial transmission line.

.........................................
Yes I agree with waveguide feed but was using it just as a example, however it has a narrow bandwidth the question I will ask is with waveguides do they all have a narrow bandwidth like the example in the picture or is it due to the high gain design?
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Re: Radio card RX bandwidth?

Sun Oct 16, 2011 7:05 pm

Hi ...
Yes I agree with waveguide feed but was using it just as a example, however it has a narrow bandwidth the question I will ask is with waveguides do they all have a narrow bandwidth like the example in the picture or is it due to the high gain design?
There's some default frequency ranges for industry standards.

I mean, a WR159 is usefull from 4.9 to 7GHz, the WR187 from 3.9 to 5.9GHz.

Now, when fitted with a probe feeder (like the photo), depends too. The untuned version normally covers all freq handled by the WG but with a return loss from 10 to 13dB and that's it. There's some techniques to prune those feeders which improve the return loss or for a single frequency or to a broader range.

The horn itself is broadband. As much long the horn is, greater the gain (and narrower the beam). And the gain is proportional to the corner opening area, like any other antenna. E.g. a horn reflector with 1 square meter will have the same gain of a solid dish with 1 square meter.

There's horns that have conical shape, so dual feeder are possible (V & H or RHCP & LHCP).

And if you expand techniques, you'll see some principles applied to the TVRO feeders (aka chaparral feeders). They're waveguide feeders equiped with scalar rings which create a 110º (@-10dB) beamwidth ... nice to iluminate a parabolic dish with f/d= 0.31 to 0.40.

There's a "primer" at a ham radio page ... http://www.qsl.net/n1bwt/chap2.pdf, may be usefull.

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Re: Radio card RX bandwidth?

Sun Oct 16, 2011 10:21 pm

with waveguides do they all have a narrow bandwidth
As mramos says, it is not the waveguide that is the likely cause of any narrow bandwidth - more likely to be the method of how they have arranged the radiating element within the short length of waveguide, before it reaches the horn antenna.
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Re: Radio card RX bandwidth?

Sun Apr 13, 2014 2:48 am

hi, I state my apologies to my English unclear, but I do not know that language and then use the google translator. resurrected this topic looking for advice and I provide my experience. in a quite busy by wisp operating at 5GHz, I mounted a sxt lite 5 as a bridge that receives a sxt 5 lite mode ap. the only clear frequency that I find is the 5320, so I set this frequency devices, 20/40MHz above protocol NV2 double chain. all in all I have a docking site on the arrival of 220MB of rx and tx 120 as a test of band I am with tcp direction with 25mb Both rx and tx 35 as average. signal as I am about to -60/-60 at a distance of 5km 45db signal-noise CCQ 50/75%, all in all not bad. the problem and do not see it very stable, I believe that it is precisely because of the abundance of frequencies occupied. So I came up with this topic that I had read some time ago. I made a lite sxt 5 to insulate the antenna ... I rummaged in the magazine and I found a spray paint of zinc, adhesive paper .. will! I am attaching pictures of my work, which I still have to assemble and test ... in the meantime, what do you think?'ll have improvements?ImageImageImageImageImageImageImageImageImageImageImage


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Re: Radio card RX bandwidth?

Mon Apr 14, 2014 12:36 pm

@microwifi
I spent a lot of time on a pair of SXT both painting on the inside conductive paint and applying copper foil to the outside, and performance was good when attached onto a mesh dish but unfortunately in a short period of time it was water ingress which forced me to withdraw the SXT from service, you may not have that problem?

There is a lot of good AP's now available which are well shielded, and now i would not spend such a long time modifying a SXT,
also zinc paint may not be conductive, I used conductive carbon paint and tested when applied with a multimeter but still had to apply a sealer over the carbon paint,
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Re: Radio card RX bandwidth?

Mon Apr 14, 2014 1:08 pm

@microwifi
I spent a lot of time on a pair of SXT both painting on the inside conductive paint and applying copper foil to the outside, and performance was good when attached onto a mesh dish but unfortunately in a short period of time it was water ingress which forced me to withdraw the SXT from service, you may not have that problem?

There is a lot of good AP's now available which are well shielded, and now i would not spend such a long time modifying a SXT,
also zinc paint may not be conductive, I used conductive carbon paint and tested when applied with a multimeter but still had to apply a sealer over the carbon paint,
Did you have one of the newer SXTs with the "water protection tunnel" as microwifi has in the pictures? We have had no water issues for quite a while already, the new SXTs are very different from the first ones. We also have shielding paint:

Image
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Re: Radio card RX bandwidth?

Mon Apr 14, 2014 2:52 pm

I still have to prove that I sxt shielded with zinc paint. To date I have not had any problem with sxt with infiltration of water. I have installed at least one year 40. did not understand if the zinc paint will give me better performance or not. in addition according to your experience with sxt quarrel with about 5km -60/-60db to 40MHz can hope for decent performance and stability? ps I also had the creamed by sxt mikrotik but I have not been able to test it in a similar condition.


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Re: Radio card RX bandwidth?

Mon Apr 14, 2014 4:17 pm

@microwifi
I spent a lot of time on a pair of SXT both painting on the inside conductive paint and applying copper foil to the outside, and performance was good when attached onto a mesh dish but unfortunately in a short period of time it was water ingress which forced me to withdraw the SXT from service, you may not have that problem?

There is a lot of good AP's now available which are well shielded, and now i would not spend such a long time modifying a SXT,
also zinc paint may not be conductive, I used conductive carbon paint and tested when applied with a multimeter but still had to apply a sealer over the carbon paint,
Did you have one of the newer SXTs with the "water protection tunnel" as microwifi has in the pictures? We have had no water issues for quite a while already, the new SXTs are very different from the first ones. We also have shielding paint:
No - unless they perform better than a 23dbi CPE which we use as standard, we will stay for now with what has proven to be very reliable, also is there vertical adjustment on the SXT mounting bracket.
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Re: Radio card RX bandwidth?

Mon Apr 14, 2014 4:20 pm

No - unless they perform better than a 23dbi CPE which we use as standard, we will stay for now with what has proven to be very reliable, also is there vertical adjustment on the SXT mounting bracket.
Sounds like a different class type of device.

QRT5 is what you need. 23dBi and precision alignment, waterproof etc.
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Re: Radio card RX bandwidth?

Mon Apr 14, 2014 4:25 pm

No - unless they perform better than a 23dbi CPE which we use as standard, we will stay for now with what has proven to be very reliable, also is there vertical adjustment on the SXT mounting bracket.
Sounds like a different class type of device.

QRT5 is what you need. 23dBi and precision alignment, waterproof etc.
And ...shielding paint...on the QRT5, if yes then a very good product.
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Re: Radio card RX bandwidth?

Mon Apr 14, 2014 4:27 pm

No - unless they perform better than a 23dbi CPE which we use as standard, we will stay for now with what has proven to be very reliable, also is there vertical adjustment on the SXT mounting bracket.
Sounds like a different class type of device.

QRT5 is what you need. 23dBi and precision alignment, waterproof etc.
And ...shielding paint...on the QRT5, if yes then a very good product.
There is a metal plate covering the backside of the unit, which works better than paint.
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Re: Radio card RX bandwidth?

Tue Apr 15, 2014 2:30 am

And ...shielding paint...on the QRT5, if yes then a very good product.
There is a metal plate covering the backside of the unit, which works better than paint.
Well, the SXT is already; how long, 3 years? on the market. So us, MT die-hards had to do with the SXT to survive in a budget war with nanobridge and nanostations..... We have been crying for better shielding for a long time. (I have done my share in painting the insides of Sextants & SXT's (and made once a test with an SXT and found the signal/noise level was dropped by some 3-4dB! So halved!)
And finally, after a very long maturing process, the NV2 protocol is also that hardened now I use the SXT's in a very noisy environment and hardly have the problems with troubled radiolinks as we had in the past....

Off course, I have been waiting long for the QRT5, as a worthy successor for the old RIC units. (Still have 30+ in the field doing their job, boards updated but antennas still performing well...)
But although the QRT5's are promised for a while now, and I have seen it in Venice, I don't seem to find any supplier yet in Europe that can deliver them to me... so haven't got a clue what the price will be..... :(
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Re: Radio card RX bandwidth?

Tue Apr 15, 2014 11:23 am

There is a metal plate covering the backside of the unit, which works better than paint.
I will keep adding to my wish list :) How about microwave foam absorber placed on the radio card side of metal plate to reduce internal signal reflections back onto the radiating elements, and option to mount if required a water-proof ethernet rj-45 socket.
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Re: Radio card RX bandwidth?

Tue Apr 15, 2014 11:56 am

There is a metal plate covering the backside of the unit, which works better than paint.
I will keep adding to my wish list :) How about microwave foam absorber placed on the radio card side of metal plate to reduce internal signal reflections back onto the radiating elements, and option to mount if required a water-proof ethernet rj-45 socket.
aaahrghh, you have too many wishes to keep the unit affordable in price! :) I'm already afraid this one is not going to be very competitive towards the new line of nanobridges...

anybody already have any knowledge of the prices?
In Venice Normis (I believe it was him) asked me/us what price we would like to see for the unit.... I replied "gratis"! (My reply was not serious, since I don't believe the question was ....)

The SXT's do very well and are price winner. I'll guess for 80% of the situations they beat nanobridges (they also have no real watertight design). For any other installations that require higher water and noise resistance I'll guess you'll have to look into high end antennas, that obviously come with a different price tag.
If the QRT's are not too much more expensive than the SXT's their higher gain (recieve!) will make them interesting for the somewhat more distant clients. They would perfectly mix in with my AP networks that now have problems to reach the distant clients while I want all associated CPE's to be in the 50-60dBi range. With SXT's that is not possible at distance more than about 4-5km's. (Yes, they have powerfull transmitters, but the receiver needs more signal too...)
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Re: Radio card RX bandwidth?

Tue Apr 15, 2014 12:06 pm

hmm, I see now the QRT5 are not even on the website (anymore?).
So why are they proposing the antenna while its not even available yet?

(Maybe they are implementing the extra wishes n21roadie mentioned! :D )
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Re: Radio card RX bandwidth?

Tue Apr 15, 2014 12:31 pm

aaahrghh, you have too many wishes to keep the unit affordable in price! :) I'm already afraid this one is not going to be very competitive towards the new line of nanobridges...

......................................
Should have listed my wish list as "Options available for ....... "
(Maybe they are implementing the extra wishes n21roadie mentioned! :D )
Ok I changed my wish list, does that mean the product is back on the website again?
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Re: Radio card RX bandwidth?

Wed May 14, 2014 5:25 am

Did you have one of the newer SXTs with the "water protection tunnel" as microwifi has in the pictures? We have had no water issues for quite a while already, the new SXTs are very different from the first ones. We also have shielding paint:

Image
Are these paint shielded units available yet?

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