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InoX
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Re: SXT reflector - 154mbps TCP

Thu Sep 01, 2011 11:00 pm

I can give examples here but this topic is not about your opinions. Stay on topic please. I will not contradict with you anymore.
 
wolfeyes
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Re: SXT reflector - 154mbps TCP

Sun Sep 04, 2011 11:18 pm

Hi All,

We've set a PtMP environment with two sector panel antennas. CPEs are all sxt devices.
For clients having a significant distance from central ap, we used same technique with dish reflector.
What we noticed while experimenting is that sxt needs to be quite distant from reflector.
In the attached photo you may see what I mean.
After applying lots of testing this was the most optimum position in our case.

@InoX. Have you tested that?
1.JPG
Signal strength is highly improved with this technique and actually it the most cost effective solution for long distance clients.
Furthermore, this setup in being used for the last 4 months without any problem at all.

In the below picture you may find signal strength values for respective sxt CPEs.
2.jpg
sxt1 is 19km far from sector and signal is -76db. I think it is great. :D
We used a second reflector for sxt3 to perform some additional testing.
We received 125mbps with nv2 of course.

Now, sxt4 is close to sxt3 but without reflector signal is -72db. sxt3 at the same distance and position with reflector reaches -62db on 5km distance!
With larger reflector we have also reached -56db from the same sxt.

From my perspective it is the most cost effective solution because takes advantage of sxt dual polarization.
For a dual polarization dish you need 200$ at least while for for a dish reflector about 20$...

Since I'm not a radio technology expert and guru I really concerned with WirelessRudy comments and had some second thoughts.
First thing I did was to disconnect SXTs having reflectors from network. I then checked noice levels but haven't been affected at all.
I'm not sure what will happen if I increase the number of clients in the future and environment becomes more complex... :?

@Mikrotik support team. I saw your interest in a previous post on this threat. Thus the question is: Is this a recommended techique for sxt installation? Will this produce potential noice problems?
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WirelessRudy
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Re: SXT reflector - 154mbps TCP

Mon Sep 05, 2011 2:46 am

@wolfeyes: Optimal positioning of an emission of a radio signal (normally by a feed horn) is located in or very close to the focal point of the dish.
If now the point of emission is actually a square surface with a diameter much bigger than the focal point (which is in fact having the size of the amplitude of the radiowave) than you can bring the ´shadow´ of the SXT on the dish more in line with the size of the dish by either moving it towards, or away from the dish. Thus increasing the total signal gain.

Moving it towards the dish has a limit. The closer the more the SXT itself will throw a ´obstruction shadow´ on the dish. In off set dishes this is not very important but in your setup it is.
Moving it away from the dish makes the ´obstruction shadow´ of the SXT projected on the dish smaller so the dish can actually gain more signal to bounce to the SXT. So you are definitely better off in your setup by removing the SXT away in stead of closer to the dish.
In the world of dish radio technology it is also accepted (and proved) that ´off set´ dishes are better. The don't have the ´obstruction shadow´ effect but are also less vulnerable for slight off aligning of the dish.
In your setup it is much more important to have the dish pinpointed to the remote point of interest than in an off set dish.
In your chosen setup with the centre focal dish combined with the greater need for accurate aligning makes it also much more important to have a sturdy setup so wind is not moving the dish.

If I now would compare a very sturdy dish fitting for the cheap dish to a good designed dome antenna which comes with a good fitting compared with probably a better signal I don't know what will be my choice in the end.
 
megabeast
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Re: SXT reflector - 154mbps TCP

Mon Sep 05, 2011 10:40 am

wolfeyes,
what is the gain of the anntena used with your AP ?
 
wolfeyes
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Re: SXT reflector - 154mbps TCP

Mon Sep 05, 2011 11:34 am

@WirelessRudy. While experimenting with sxt position, we also evaluated the offset topology but for some bizarre reason performance was not as good as the current position with the sxt in front and away from the dish.
This led us to apply the steady construction with the metal brackets shown in picture.
Indeed we also noticed the alignment to the pinpoint is more sensitive but once this achieved results are very encouraging.
Numbers prove it:
For distance 19km we get -76db and for distance 5km we get -60db.
And always have in mind that the additional cost per client is just 20$. 8)


@megabeast. Sector gain is 17dbi. From my point of view the key point in this setup is the dual sector antenna HV polarity which takes full advantage of the dual sxt HV polarization.
 
WirelessRudy
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Re: SXT reflector - 154mbps TCP

Mon Sep 05, 2011 12:18 pm

@WirelessRudy. While experimenting with sxt position, we also evaluated the offset topology but for some bizarre reason performance was not as good as the current position with the sxt in front and away from the dish.
Imho this can be a result of the SXT not being a horn-feed antenna but a micro-print with bigger surface than the focal point will have to reach.
For distance 19km we get -76db and for distance 5km we get -60db.
I never questioned the increase in db's due the use of a dish. I argued that the use of an SXT also might have negative effects compared to a feed horn. Its not only pluses we get. Your findings actually proof that what might work in one situation doesn't always work in another.

But I am fair enough to agree that in many real situations the overall performance is better than without the dish.
 
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mahnet
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Re: SXT reflector - 154mbps TCP

Mon Sep 05, 2011 6:27 pm

What good is a SXT with such big dishes....when signal is -60 at 5 km.
I have 5 km links with sxt on both sides and no big dishes. signal -51/53.
Another link 13km with groove and 24dbi grid and sxt at client end and signal -61/64.
 
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Re: SXT reflector - 154mbps TCP

Mon Sep 05, 2011 9:30 pm

What good is a SXT with such big dishes....when signal is -60 at 5 km.
I have 5 km links with sxt on both sides and no big dishes. signal -51/53.
Another link 13km with groove and 24dbi grid and sxt at client end and signal -61/64.
One of the big advantages apart from extra signal is reduced beamwidth which would be less prone to pick up of interference, for example SXT has 25º but put in front of 60cm dish and beamwidth is now 4º to 5º.
 
wolfeyes
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Re: SXT reflector - 154mbps TCP

Mon Sep 05, 2011 10:19 pm

What good is a SXT with such big dishes....when signal is -60 at 5 km.
I have 5 km links with sxt on both sides and no big dishes. signal -51/53.
Another link 13km with groove and 24dbi grid and sxt at client end and signal -61/64.
It is expected to have such signal levels in your case, since you use directional antennas on both sides of your links.
 
megabeast
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Re: SXT reflector - 154mbps TCP

Tue Sep 06, 2011 11:00 pm

What good is a SXT with such big dishes....when signal is -60 at 5 km.
I have 5 km links with sxt on both sides and no big dishes. signal -51/53.
Another link 13km with groove and 24dbi grid and sxt at client end and signal -61/64.
easy with that dbms for 5km link with SXT w/o reflectors.
You have two integrated antenas with 16dbm gain.
5km is about 121 dbm path lost.
Wich means, you SXT must have 38dbm RF output. And this is in under ideal conditions.
As I can see, SXT maximum RF output is no more than 25 dbm at 6mbps.
To have this power, you must have something in an odd frensel zone.

In normal conditions, you signal must be about -74dbm, for HT40-7

wolfeyes,
HV antenna only allows you 2 spatial streams and then you can have all of HT40s, which actuallly boost you link to maximum MCS-15.
SXT is comming with integrated dual polarity antenna
 
InoX
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Re: SXT reflector - 154mbps TCP

Wed Sep 07, 2011 2:09 am

What good is a SXT with such big dishes....when signal is -60 at 5 km.
I have 5 km links with sxt on both sides and no big dishes. signal -51/53.
Another link 13km with groove and 24dbi grid and sxt at client end and signal -61/64.
I had -65 at 2km with perfect loss ,without offsets...
 
birman
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Re: SXT reflector - 154mbps TCP

Wed Jan 04, 2012 12:30 pm

Sorry for off-topic.

If someone can help me and say how where I can found tutorial to configure priorities (Queue Tree) in my Mikrotik RBs.I configured Filter Rules (77 items) and I added Layer7 Protocols.

Thanks!
 
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Re: SXT reflector - 154mbps TCP

Sat Jan 07, 2012 2:16 pm

@wolfeyes!
Can you share some information about your reflectors? what is dish size? what is distance from dish centre to arm for sxt?
 
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winet
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Re: SXT reflector - 154mbps TCP

Thu Jan 19, 2012 4:19 pm

can we use digital satelite TV dish as a reflector? as far as i know, they're using 5Ghz frequency too.
 
n21roadie
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Re: SXT reflector - 154mbps TCP

Thu Jan 19, 2012 8:41 pm

can we use digital satelite TV dish as a reflector? as far as i know, they're using 5Ghz frequency too.
C band satellite yes but you may need to adjust the focal length ( distance from dish to SXT ) to peak the gain.
 
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Re: SXT reflector - 154mbps TCP

Fri Feb 17, 2012 9:22 pm

Another factor which should be considered is that the vertical and horizontal beamwidths of an offset dish are not the same. They are designed to focus on a satellite but ignore adjacent ones a couple of degrees either side at 12GHz. The vertical beamwidth is often two to three times wider.

Beamwidth will widen in proportion to the operating frequency so expect the beamwidth to double at 5.8GHz compared to the published figures which assume 12GHz. Also gain will go down by 3dB.

I'm thinking that 'reducing interference' with the big dish is more a case of having the same interference level (xxdBm) as before but the extra 10dB received signal strength is improving the carrier/interference (C/I) ratio by 10dB and enabling higher modulation schemes to function and improve throughput.

I've always worked with the following C/I ratios in the past:
  • 11mbit needs at least 15dB C/I
  • 54mbit needs at least 28dB C/I
  • 65mbit needs at least 30dB C/I
If you can't guarantee these ratios the modulation will fail to be decoded properly and will result in data errors and retries.

Hope this is useful, please contact me if you need more information.

andy
 
InoX
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Re: SXT reflector - 154mbps TCP

Sat Feb 18, 2012 2:21 am

to much calculations instead of practice, important thing is that is working much better than before and I have 4 of them in bonding with speed of ~330mbps.
 
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winet
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Re: SXT reflector - 154mbps TCP

Sat Feb 18, 2012 3:58 pm

exact calculation is important when you're about to do mass production :lol:
i'm considering placing dish reflector on every client i have.
 
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saintofinternet
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Re: SXT reflector

Mon Aug 19, 2013 4:56 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 ;)
regards

your 7 kms is given me a big hope.

can i stretch it for another 5 kms?? a total of 12 kms clear LOS??

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