thanks for your reply,but so far i have not seen any data about the receive bandwidth spec on the manufacturer's datasheets?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......
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.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.
What is the specific card you are looking for data on?so far i have not seen any data about the receive bandwidth spec on the manufacturer's datasheets?
Please expand what you mean by that statement.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.
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.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)
XR5 for starters?What is the specific card you are looking for data on?
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.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.
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.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!
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).no - not generating rf outside it's assigned channel
- 16dBi 4.9-6.0Ghz Sectoral Gain, http://www.itelite.net/offer.php?n=36&lang=enStill not sure what a "full spectrum antenna" is exactly.
Why is this? I would think it is the middle frequency. So a 5.4 to 5.7Ghz antenna would perform best at 5500Mhz?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.
BAW resonator = ??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.
IMD = ??3rd order IMD performance of the LNA of the wifi card.
Ha! That's good one! Hence MT has so much problems getting nv2 properly to work in heavy crowded spectrum situations.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!
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.Why is this? I would think it is the middle frequency. So a 5.4 to 5.7Ghz antenna would perform best at 5500Mhz?
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,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.
What is the best AP antenna for price and performance for 5.8ghz?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'.
Same question - what is the best radio card for price performance,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!
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.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,
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.What is the best AP antenna for price and performance for 5.8ghz?
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".Same question - what is the best radio card for price performance,
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"You mean moving the antenna backwards and forwards horizontally? The other problem is the casing of that CPE is plastic.
Aah no harm in askingHow 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
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).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"
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.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.
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 = 80mw1m of very low loss coax will only drop the signal by about 2dB approx
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,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?
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?..we advised spraying the inside of their Mikrotik Outdoor case with Nickel RF Screening spray paint and this was very effective at reducing interference).
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?a 20.5Km ptp link which has a fade margin of 29dB
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!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?
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.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!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?
I was trying to include as few "Bankers" in that beamhe 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?
I use http://www.ligowave.com/linkcalc/ XR5 23dbm @54Mhz, grid 24dbi, cable loss 2db, -91dbm (had-94?) = 27db fade margin and +47dbm(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)
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.
Hi Marcus,Hi ...
Nice topic.
About the receiver BB filter, there is a pix from a chipset manufacturer.
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
I think this graph created more confusion than clear things up but is somewhat simple.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?
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.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?
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).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?
Yes only one radio card - 433AH +XR5To refresh the details.... each antenna has an enclosure containing only one radio correct?
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,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.
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.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.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?
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.
That's clear now too.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).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?
I'm eagerly awaiting your comments...OFDM errors later
...So the first stage at the receiver will see everything from 5.1 to 5.9GHz.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.
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Regards;
That's it....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.
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.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
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.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.
I guess it should solve it all - if - the tx & rx cycles could be synched to some time slot (like NV2, tdma, etc).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?
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.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.
Over 1 min scan duration the -11 went to -12 and -10?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?
It's coming off another sector AP on the mast 5865I 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.
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.Over 1 min scan duration the -11 went to -12 and -10?
Rudy can you give me the brand of sink paint did you use and is it conductive for earthing?.............................................................
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!
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.Rudy can you give me the brand of sink paint did you use and is it conductive for earthing?.............................................................
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!
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,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.
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.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.
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As you are finding out, it is not until every single box is done, that you will see all this hard work being worthwhile.
When you refer to "antenna", you actually mean the enclosure the antenna sits inside - right?the parts i screened on the antenna
Enclosure - correct,When you refer to "antenna", you actually mean the enclosure the antenna sits inside - right?the parts i screened on the antenna
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!
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.As regards screening the feed to the dipole on a grid antenna the only item i have seen so far is this design
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?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.As regards screening the feed to the dipole on a grid antenna the only item i have seen so far is this design
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There's some default frequency ranges for industry standards.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?
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.with waveguides do they all have a narrow bandwidth
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:@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,
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.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:@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,
Sounds like a different class type of device.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.
And ...shielding paint...on the QRT5, if yes then a very good product.Sounds like a different class type of device.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.
QRT5 is what you need. 23dBi and precision alignment, waterproof etc.
There is a metal plate covering the backside of the unit, which works better than paint.And ...shielding paint...on the QRT5, if yes then a very good product.Sounds like a different class type of device.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.
QRT5 is what you need. 23dBi and precision alignment, waterproof etc.
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!)There is a metal plate covering the backside of the unit, which works better than paint.And ...shielding paint...on the QRT5, if yes then a very good product.
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.There is a metal plate covering the backside of the unit, which works better than paint.
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...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.There is a metal plate covering the backside of the unit, which works better than paint.
Should have listed my wish list as "Options available for ....... "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...
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Ok I changed my wish list, does that mean the product is back on the website again?(Maybe they are implementing the extra wishes n21roadie mentioned! )
Are these paint shielded units available yet?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: