SXT reflector - 154mbps TCP
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InoX
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SXT reflector - 154mbps TCP

by InoX » Tue Jun 28, 2011 10:57 pm

Reflector have 55cm and add 10dbi of gain, total of 20dbi for both.
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Re: SXT reflector

by InoX » Tue Jun 28, 2011 10:59 pm

and some more...
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Re: SXT reflector

by n21roadie » Wed Jun 29, 2011 2:15 am

Reflector have 55cm and add 10dbi of gain, total of 20dbi for both.

Is 20dBi good with that hardware ?
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Re: SXT reflector

by mahnet » Wed Jun 29, 2011 5:49 am

the arrangement looks awesome
but the specs of SXT say it has a 16dbi antenna and I am running a 7 km link with 2 SXT's PtP and clear LOS and throughput of more than 10 mbps.
Adding the reflector for a gain of just 4 dbi.....is it justified. I guess adding a reflector 2 gain another 20 dbi should be worth. OR may be thats the way ur arrangement works.....16 dbi from SXT + 20 dbi from reflector = Total gain 36 dbi .

Am i getting clumsy ;)
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Re: SXT reflector

by Tanuki » Wed Jun 29, 2011 7:16 am

I read it as 10dBi of extra gain on top of the 16dBi already provided by the SXT's built antenna - for a total of 26dBi per end.

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Re: SXT reflector

by InoX » Wed Jun 29, 2011 2:54 pm

mahnet wrote:the arrangement looks awesome
but the specs of SXT say it has a 16dbi antenna and I am running a 7 km link with 2 SXT's PtP and clear LOS and throughput of more than 10 mbps.
Adding the reflector for a gain of just 4 dbi.....is it justified. I guess adding a reflector 2 gain another 20 dbi should be worth. OR may be thats the way ur arrangement works.....16 dbi from SXT + 20 dbi from reflector = Total gain 36 dbi .

Am i getting clumsy ;)
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Read again.
The link was -68 and now -45. I said "adds 10dbi", a 55cm offset antenna will always have 25-26dbi and you can't just do tha math like 16+26=42. The SXT just act like an feeder now. Anyway the gain is more than 20dbi for link and I'm happy. Costs was 15$/offset and 30min of work. The goal was the beat the interference and that what it did. From 60-80mbps with 25ms average to 140mbps with 5ms at 100mps.
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Re: SXT reflector

by n21roadie » Wed Jun 29, 2011 3:39 pm

InoX wrote:Read again.
The link was -68 and now -45. I said "adds 10dbi", a 55cm offset antenna will always have 25-26dbi and you can't just do tha math like 16+26=42. The SXT just act like an feeder now. Anyway the gain is more than 20dbi for link and I'm happy. Costs was 15$/offset and 30min of work. The goal was the beat the interference and that what it did. From 60-80mbps with 25ms average to 140mbps with 5ms at 100mps.

What is distance between the both points, you mentioned it "best the interference" could the narrower angle of pick-up by the dish's helped this rather than just using SXT, also well done on the DIY how did you peak the gain from both dishes?
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Re: SXT reflector

by mahnet » Wed Jun 29, 2011 7:38 pm

wht is the distance betn the links??

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Re: SXT reflector

by InoX » Wed Jun 29, 2011 9:24 pm

2km

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Re: SXT reflector

by Matess » Fri Jul 01, 2011 1:20 am

InoX wrote:Read again.
The link was -68 and now -45. I said "adds 10dbi", a 55cm offset antenna will always have 25-26dbi and you can't just do tha math like 16+26=42. The SXT just act like an feeder now. Anyway the gain is more than 20dbi for link and I'm happy. Costs was 15$/offset and 30min of work. The goal was the beat the interference and that what it did. From 60-80mbps with 25ms average to 140mbps with 5ms at 100mps.


Hi, how can i calculate tx-power in this case?

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Re: SXT reflector

by InoX » Fri Jul 01, 2011 1:43 am

26dbm(SXT)+26dbi(reflector)=52dbm

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Re: SXT reflector

by Matess » Sun Jul 03, 2011 6:13 pm

thanks... other question... how can i calculate gain of offset antena? Lets say 60cm, 80cm, 100cm, 110cm....

if i know....
dBm(power)+dBi(anntena gain)-2,6 = dBm

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Re: SXT reflector

by InoX » Sun Jul 03, 2011 9:13 pm

60cm-26dbi
80-90cm-29-30dbi
don't know about a calculator.

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Re: SXT reflector

by n21roadie » Sun Jul 03, 2011 9:19 pm

InoX wrote:26dbm(SXT)+26dbi(reflector)=52dbm

I would assume this can only be true of perfect alignment at a particular frequency and not above or below this frequency but the best actual alignment obtained can have gain figures much less than quoted.
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Re: SXT reflector

by InoX » Mon Jul 04, 2011 1:15 am

You can assume it's not raining, there are no birds in the way, no dust, no air...you get the point.

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Re: SXT reflector

by n21roadie » Mon Jul 04, 2011 1:01 pm

InoX wrote:You can assume it's not raining, there are no birds in the way, no dust, no air...you get the point.

Once again i must praise your DIY effort on this link and all i what to ask is how much actual gain will be achieved after such efforts, Can i ask what was the signal level at both sides of this 2KM link before and after the SXT reflector,
To date i have only seen prime focus solid dish's used for 5-6Ghz and my guess is the 55cm dish in the photo's is a modified offset satellite dish, i quote some theory "The theoretical gain (directive gain) of a dish increases as the frequency increases. The actual gain depends on many factors including surface finish, accuracy of shape, feedhorn matching.."
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Re: SXT reflector

by InoX » Mon Jul 04, 2011 2:24 pm

before was -68 and after -43 as I said . Offset is not modified; it just has a flex pipe (upper one;PEXAL pipe - plastic and aluminium) inside the arm, and the other, because there are the same but not identical, I had to invent another system out of toilet pipes. Any antenna varies in frecvency but the offset just add more gain to the SXT antenna, so there will be some dbi more or less.

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Re: SXT reflector

by n21roadie » Mon Jul 04, 2011 3:00 pm

InoX wrote:before was -68 and after -43 as I said . Offset is not modified; it just has a flex pipe (upper one;PEXAL pipe - plastic and aluminium) inside the arm, and the other, because there are the same but not identical, I had to invent another system out of toilet pipes. Any antenna varies in frecvency but the offset just add more gain to the SXT antenna, so there will be some dbi more or less.

Wow what a improvement in signal, did you find the signal varied by a lot if the SXT was moved closer or further from dish on the support arm?
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Re: SXT reflector

by InoX » Mon Jul 04, 2011 8:57 pm

No, as you can see in the pictures the upper one is more distant from dish, and this is how should be. The lower antenna have the SXT too close, so not quite in the focal point, but still work and the same gain.

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Re: SXT reflector

by InoX » Sat Jul 09, 2011 1:50 am

New record with SXT 154mbps TCP.
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Re: SXT reflector

by mahnet » Sat Jul 09, 2011 8:17 pm

InoX wrote:New record with SXT 154mbps TCP.


how can u add the traffic on ether1 and wlan1 it is incorrect. ur ether1 is only recieving what ur wlan1 is transmitting.

now i doubt ur case ;-)

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Re: SXT reflector

by petrn » Sat Jul 09, 2011 8:54 pm

mahnet wrote:
InoX wrote:New record with SXT 154mbps TCP.


how can u add the traffic on ether1 and wlan1 it is incorrect. ur ether1 is only recieving what ur wlan1 is transmitting.
he added wlan1 TX and RX - same way as MT do when they claim RB-SXT 200mbps

now i doubt ur case ;-)

and i doubt yours
Petr

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Re: SXT reflector

by InoX » Sun Jul 10, 2011 12:38 am

mahnet wrote:
InoX wrote:New record with SXT 154mbps TCP.


how can u add the traffic on ether1 and wlan1 it is incorrect. ur ether1 is only recieving what ur wlan1 is transmitting.

now i doubt ur case ;-)

Because the traffic goes from lan to wlan? And is a bidirectional traffic and you can make the math from rx and tx? I wonder how satisfied are your clients with your services...
Now I've edited the picture for more understanding purposes and kids.
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Re: SXT reflector

by mahnet » Sun Jul 10, 2011 2:16 pm

InoX wrote:
mahnet wrote:
InoX wrote:New record with SXT 154mbps TCP.


how can u add the traffic on ether1 and wlan1 it is incorrect. ur ether1 is only recieving what ur wlan1 is transmitting.

now i doubt ur case ;-)

Because the traffic goes from lan to wlan? And is a bidirectional traffic and you can make the math from rx and tx? I wonder how satisfied are your clients with your services...
Now I've edited the picture for more understanding purposes and kids.



I think performance depends on what u deliver and not just numbers. If such is the case with MT that they add up TX and RX to calculate 200 mbps it is upto them. We are happily delivering 20 mbps TX and 20 mbps RX and we claim just 20 mbps. Not that we add them up to make 40 mbps. If a client comes to us asking 2 mbps bandwidth we dont give them 1mbps Tx and 1 mbps Rx. We deliver 2 mbps TX and 2 mbps Rx.
Our clients are more than happy for what we commit and what we deliver. If we dont find radios deliver we have our OFC network. If thats not feasible we have several backhauls all over.

Now I understand why is the bandwidth market getting dicey and some people quoting unrealistic <low> prices

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Re: SXT reflector - 154mbps TCP

by uldis » Mon Jul 11, 2011 12:08 pm

InoX, that speed 154Mbps TCP is on that 2km link?

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Re: SXT reflector - 154mbps TCP

by InoX » Mon Jul 11, 2011 12:13 pm

Yes. We have a tower that needs a lot of speed and we make two SXT links for over 200mbps trafic. In summer we are not alowed to install fiber because of the turists. Without offset, the links interfered with 7 links on the tower and were very unstable. Without nv2 are not working.

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Re: SXT reflector - 154mbps TCP

by WirelessRudy » Mon Aug 29, 2011 1:53 am

InoX wrote:Without offset, the links interfered with 7 links on the tower and were very unstable. Without nv2 are not working.
Although some dated topic: Can you explain your theory why the use of the dish is reducing the interference problem you say you had before? All you do is increasing the signal levels on your link. The dish is not helping removing any interference from other units....

Apart from that, nice job to use SXT like this. It does improve signal levels. But is doesn't stop other link issues like interferences. I'd prefer radio's in metal/shielded box and just high gain directional antenna.
The SXT has already been proven very vulnerable to interferences due its plastic casing....
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Re: SXT reflector - 154mbps TCP

by InoX » Mon Aug 29, 2011 5:14 am

narrow beam means less noise...you are repeating yourself to much.

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Re: SXT reflector - 154mbps TCP

by n21roadie » Mon Aug 29, 2011 12:40 pm

[quote="WirelessRudy]....... All you do is increasing the signal levels on your link. The dish is not helping removing any interference from other units....

....[/quote]
While the dish has a narrower beamwidth say 6 degree's (?) the SXT has 25degree's and because of the plastic moulded constuction which does not give any shielding could and probally would pick up local interference from other units on a mast being mounted on the offset arm of the dish, possible solution is to mount the SXT inside a shielded cylinder can.
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Re: SXT reflector - 154mbps TCP

by WirelessRudy » Mon Aug 29, 2011 2:20 pm

InoX wrote:narrow beam means less noise

Putting it that simple is only partly true in relation to your setup. How did you calculate the exact location of the SXT? Just putting it on the LNB stand-off pipe is not good enough. Normally an LNB has its feedhorn located exactly at the apparent phase center (or focal point) and is just big enough to let the electromagnetic waves of use pass.
The SXT antenna in fact consists out of a array of small antenna's. Because they are stretched over some 13cm radius only the ones direct in the focal point will pick up the signal the dish should collect. Any microstrip antenna outside the direct focal point will pick up signals that are just beside the working beam of the dish.
To eliminate this and to only have the desired signal hitting the full array of the SXT you have to move the SXT away (in front or behind) from the actual focal point.

Fitting an SXT simply on the pole that held the LNB before mainly only increased your link signal strength because the dish simply gathers more energy from remote transmitter. Only because your SXT physical design is such the actual antenna is closer to the dish than the original LNB by luck you probably put the antenna in enough off-set from the focal point not to make things too bad.
At the same time, the reversed for receipt counts on the transmitting end. Putting the SXT in the wrong position might still increase signal strength at remote receiver but also spreads more off beam signals in the spectrum, more noise for others.....

Using an SXT in front of a dish to get better signals is the same as putting a 10.000 horsepower ships engine in a tractor to win the grand prix. As long as your race is not interfered with curves and other outside factors you'd probably win the race from any high tuned F1 car! But when the environment becomes a bit more complicated its a guaranteed loser.

Without proper calculated location of the receiver antenna in relation to the dish you are merely guessing and hoping the best.....
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Re: SXT reflector - 154mbps TCP

by WirelessRudy » Mon Aug 29, 2011 2:29 pm

n21roadie wrote:[quote="WirelessRudy]....... All you do is increasing the signal levels on your link. The dish is not helping removing any interference from other units....

....[/quote]
While the dish has a narrower beamwidth say 6 degree's (?) the SXT has 25degree's and because of the plastic moulded constuction which does not give any shielding could and probally would pick up local interference from other units on a mast being mounted on the offset arm of the dish, possible solution is to mount the SXT inside a shielded cylinder can.[/quote][/quote][/quote]
I didn't even want to mention that. I agree, the plastic design of the SXT will pickup signals from everywhere exept maybe from direct behind the dish! I found the SXT's indeed are not doing very good in heavy congested spectrum circumstances. This counts nevertheless its fitted at an dish or not.

We already discussed before that in fact it is a pity the industry focusses so much on high power radio's and a lot of amateurs play with shields and dishes in search for even higher signal levels.
Understanding radio wave behaviours and its underlying technology in respect of the use of proper antenna's can do much more than simply increasing signal strengths.
A good designed antenna bound to a very high sensitive receiver combined with the proper filters etc. could probably pick up an wifi router on the moon!
In fact that is what scientist do when listening to the weakest signals from outer space. All they can do is develop the best ´listening´ technology to ´hear´ the other end. They have no control over send power!
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Re: SXT reflector - 154mbps TCP

by ottoshr » Mon Aug 29, 2011 6:48 pm

inox
why there is 2 antennas ? dou you use both polarization in each of them? doe'snt they are in each other fresnel zone ?

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Re: SXT reflector - 154mbps TCP

by WirelessRudy » Mon Aug 29, 2011 8:04 pm

ottoshr wrote:inox
why there is 2 antennas ? dou you use both polarization in each of them? doe'snt they are in each other fresnel zone ?
For each polarization you need one antenna. They can both be fit into one array/housing so it looks as one. For the full benefit of mimo (802.11n) you need two chains (=send or receive device = antenna) to get to the high throughputs like 300Mbps (theoretical maximum!) With only one chain you only get 150Mbps max.
Fresnel zone has nothing to do with dual polorized antenna's in itself.
Fresnel zone has influence on any (wifi) radio link no matter what protocol is used.
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Re: SXT reflector - 154mbps TCP

by ottoshr » Mon Aug 29, 2011 8:10 pm

ok, but SXT has allready two chains ! why inox need two antennas for two chains ?

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Re: SXT reflector - 154mbps TCP

by WirelessRudy » Mon Aug 29, 2011 8:23 pm

ottoshr wrote:ok, but SXT has allready two chains ! why inox need two antennas for two chains ?
Ah, I see what you mean. He uses two links to bridge the same towers and to get 200Mbps+ traffic.
In itself two links can transport double the amount of one was it not you have to make sure interference is not playing a part between them.

The way I look at the whole of his setup he'd better study a bit more on radio links and try to achieve what he wants with only one link but better building material (antenna's).
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Re: SXT reflector - 154mbps TCP

by ottoshr » Mon Aug 29, 2011 8:31 pm

how with mikrotik get two links working together , you mean sinchronised ? in bridge ?

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Re: SXT reflector - 154mbps TCP

by WirelessRudy » Tue Aug 30, 2011 1:41 am

ottoshr wrote:how with mikrotik get two links working together , you mean sinchronised ? in bridge ?

http://wiki.mikrotik.com/wiki/Bonding
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Re: SXT reflector - 154mbps TCP

by InoX » Tue Aug 30, 2011 4:22 am

I use both chains in both links and they are not sensitive to noise. Each link can carry ~150mbps, so I dont need any more setup or antennas. The links are not bonded. Read more carefully.

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Re: SXT reflector - 154mbps TCP

by WirelessRudy » Tue Aug 30, 2011 2:31 pm

InoX wrote:I use both chains in both links and they are not sensitive to noise. Each link can carry ~150mbps, so I dont need any more setup or antennas. The links are not bonded. Read more carefully.
Nobody claims your both links are bonded. Read more carefully....

Apart from that, 150mbps is 50% of the theoretical speed you could achieve with a single link consisting of 2 SXT's.
Why you use two links to reach 300mbps (in theory) makes no sense to me. You waist resources and spectrum unless you have a need for 2 separate links running side by side?

Are you using upper or lower extension channel on each of the links? If not 150mbps is the max. limit for SXT dual chain anyway.
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Re: SXT reflector - 154mbps TCP

by InoX » Tue Aug 30, 2011 7:02 pm

WirelessRudy wrote:Apart from that, 150mbps is 50% of the theoretical speed you could achieve with a single link consisting of 2 SXT's.
Why you use two links to reach 300mbps (in theory) makes no sense to me.
If not 150mbps is the max. limit for SXT dual chain anyway.

:lol: I really dont understand anything. SXT can carry 150mbps not 300mbps. 2 links=300mbps. Where do you see that SXT can reach 300mbps? Maybe 300mbps air rate...and thats another thing. :lol:

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Re: SXT reflector - 154mbps TCP

by WirelessRudy » Tue Aug 30, 2011 7:53 pm

InoX wrote:
WirelessRudy wrote:Apart from that, 150mbps is 50% of the theoretical speed you could achieve with a single link consisting of 2 SXT's.
Why you use two links to reach 300mbps (in theory) makes no sense to me.
If not 150mbps is the max. limit for SXT dual chain anyway.

:lol: I really dont understand anything. SXT can carry 150mbps not 300mbps. 2 links=300mbps. Where do you see that SXT can reach 300mbps? Maybe 300mbps air rate...and thats another thing. :lol:

The ´n´ protocol is capable of handling up to 300mbps. Off course real live real data throughput is always lower.
The brochure (http://routerboard.com/pricelist/downlo ... ile_id=267) clearly states 200Mbps real data throughput. MT is here a bit more on the reality side than most other vendors that claim they can achieve 300Mbps data with their mimo stuff.
Bottom line, if you use SXT you should be able to achieve 200Mbps tcp througput on a link and at times even higher combined with udp traffic.

You already achieved 154mbps with only 270mbps connection rate. So you actually already proof yourself better than 150mb is possible.

Reason for not reaching higher conn. rate/througputt is most probably not optimum link quality. And that is what this topic was started all about. Putting a SXT in front of a dish like you did is ok, but not the best solution to achieve the highest link capacity. That's what I am all about.

This forum is not to discuss just between you and me. Others are reading and trying to learn or picking ideas. I just put your enthusiast start of this topic in a bit wider perspective.

And we were also wondering why you needed two parallel links to achieve 300Mbps but than not bound these two into one big pipe?

Just keep on smiling.... :)
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Re: SXT reflector - 154mbps TCP

by InoX » Tue Aug 30, 2011 8:35 pm

I never read about someone to be very happy with bonding 2 links and I dont want to waste my and customers time and stiil cant understand what are you saying. You are contradicting yourself in most of the posts...maybe my english is not quite good.

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Re: SXT reflector - 154mbps TCP

by WirelessRudy » Wed Aug 31, 2011 12:56 am

InoX wrote:I never read about someone to be very happy with bonding 2 links and I dont want to waste my and customers time and stiil cant understand what are you saying. You are contradicting yourself in most of the posts...maybe my english is not quite good.
Well, for English lessons this forum is not mend so I'm afraid I can't help you here. But to discuss ROS and wireless this is the perfect forum....!

Bonding is nothing more than a way to combine 2 or more links into one big virtual one so traffic flow uses both and in case one link fails you still have the other one left. So it has redundancy built in. In your case, put both SXT links in a bounding setup and you have a virtual pipe of theoretically 400mbps tcp!

How are you using the two parallel links? Are they both used for the same data? Or do they both have different purposes? If you just use a sort of load-balancing in case they are just two links transporting the same data than bonding can even further increase you capacity. On two separate links it can be you saturate one while the other is still rather idle. A bonded line only saturates if the total capacity is used up....
This info can be interesting to other readers.....
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Re: SXT reflector - 154mbps TCP

by InoX » Wed Aug 31, 2011 1:34 am

sure, on paper...

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Re: SXT reflector - 154mbps TCP

by megabeast » Wed Aug 31, 2011 11:35 pm

InoX,
as I understood from the pictures and the internet, focus sat is a DTH (or sattelite, or DVB-S) operator, and you are using 60cm dishes that actually is used for DVB-S recievers ? And as I know, these dishes are designed for 10-12 gHz.
Please, confirm that till tomarrow afternoon, and I will try it here (with dishesh of a similar DTH operator) until end of the day and will post the results for 4km link.

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Re: SXT reflector - 154mbps TCP

by WirelessRudy » Thu Sep 01, 2011 12:46 am

megabeast wrote:InoX,
as I understood from the pictures and the internet, focus sat is a DTH (or sattelite, or DVB-S) operator, and you are using 60cm dishes that actually is used for DVB-S recievers ? And as I know, these dishes are designed for 10-12 gHz.
Please, confirm that till tomarrow afternoon, and I will try it here (with dishesh of a similar DTH operator) until end of the day and will post the results for 4km link.
Reflection done by the dish is independent of the microwave length (frequency). As long as the wave amplitude is not measured in meters the result is relatively the same. The LNB on the other hand has to be tuned for the working frequency. But the dish can serve any frequency to the same level. So it is ok to use a satellite dish for wifi signals. Wavelengths are measured in cm's here.
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Re: SXT reflector - 154mbps TCP

by InoX » Thu Sep 01, 2011 8:56 pm

Reflection done by the dish is independent of the microwave length (frequency)

WRONG!
But the dish can serve any frequency to the same level.

WRONG AGAIN!
megabeast wrote:InoX,
as I understood from the pictures and the internet, focus sat is a DTH (or sattelite, or DVB-S) operator, and you are using 60cm dishes that actually is used for DVB-S recievers ? And as I know, these dishes are designed for 10-12 gHz.
Please, confirm that till tomarrow afternoon, and I will try it here (with dishesh of a similar DTH operator) until end of the day and will post the results for 4km link.

Standard satellite dish. be aware that not all the offset antennas can tilt enough for a straight line radio wave.

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Re: SXT reflector - 154mbps TCP

by megabeast » Thu Sep 01, 2011 9:35 pm

Well Done. InoX!
A brilliant idea. 10 dbm+, just for 15 bucks! And for a device which is cheap enough.
Once again, thanx for the idea.
I tried it today, but did some improvements with the pipes.
Total 10 dbm for a dish. The link is about 4.8 km. The signal raises from -74dbm to -55dbm. The modulation raises from 150 to 270 mbps. CCQ increases from 50% to 90%, which means the noise from other nearest devices is significally decreased.
btw, I suspect that the gain is more than 10 dbm, because the cards are transmitting at lower power on higher speed modulation. Can someone tell where the see what is the actual TX power ?
Also, I think the link doesn't have clear LOS. Our binocular is a bit unusable.

About the speed of the link, I have to wait 1 day the device to calibrate itself and the to try a real speed, not just their Bandwidth test.
And an obsevation, the dish not an exact circle, but an elipsoid, so one of channel is gaining 2-3 dbm more than the other.

So, this is a cheap and usefull reflector for SXT devices!

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Re: SXT reflector - 154mbps TCP

by n21roadie » Thu Sep 01, 2011 10:08 pm

WirelessRudy wrote:Reflection done by the dish is independent of the microwave length (frequency). As long as the wave amplitude is not measured in meters the result is relatively the same. The LNB on the other hand has to be tuned for the working frequency. But the dish can serve any frequency to the same level. So it is ok to use a satellite dish for wifi signals. Wavelengths are measured in cm's here.

Yes we are talking about wavelengths of cms here but if you want to peak the gain, a prime focus would make that task easier while moving the SXT closer or further in the focal length to use the max size of the dish.
N21roadie,
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Re: SXT reflector - 154mbps TCP

by WirelessRudy » Thu Sep 01, 2011 10:50 pm

inox; Read this document: http://www.antenna-theory.com/antennas/ ... s/dish.php

It clearly tells you how right I am. For microwave band signal the reflection of the dish is all the same. (2-28Ghz!)
If this was not true you couldn't use it for 5Ghz right? It's a satellite dish, usually for 10Ghz or higher.


n21roadie hits the bullseye. To pick up as much gain as possible with an shield antenna (= parabol) that is clearly much bigger than the wavelength a dish is doing fine. But since all signal is concentrated in a circle as big as the waves amplitude, 2-3cm. (focal point) the SXT is too big an antenna compared to the focal point size.
Meaning that everything outside the footprint of the focal point on the SXT surface are signals we actually don't want. But since the SXT still has a considerable part of its gain produced here we will also pick up more unwanted signals. Because the dish also picks up more of these.

To bring the footprint of the focal ring to fill the full size of the SXT we have to move the SXT much closer to the dish.
Side effect is that now radio signals will also hit same SXT antenna more out of phase (because only in the focal centre point all waves are in phase) so that will decrease the quality of the signal. 802.11a/b/g will suffer from this, but 802.11n might actually profit from this depending on which coding scheme is used.
It is obviously that funded testing is needed which coding works best, like that always has to be done with ´n´ links anyway.

My argument in general is still standing firm. Stating that signal strength has increased is right and a simple conclusion most of us can imagine.
Stating that interferences are decreased due the same use of a dish is really unfunded and can't be proven true only because your link performs better.

A dish will definitely help in increasing the signal level but for tough spectrum conditions where best possible performance is required a better more professional antenna (or Feed horn for the specific purpose on a precisely calculated distance of the dish) is a better choice. Just putting an SXT on the LNB is a very amateurish approach that only by luck gives better performances in some situations.

And like before, we completely discard the fact that the SXT is still a poor product when it comes to shielding against signals coming from everywhere except the dish. Just run a scan in a busy spectrum and see how much signals the antenna picks up, even from the back!


P.S.
I have been called an ´amateur´ in this forum before with my 250 clients based network that earns me my money for years while beating the ´big´ carriers in price/performance and serving clients where nobody else want to go. So don't be offended by the term "amateur". :)
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