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Neighbour beams and satellite re-alignments

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frankie
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Neighbour beams and satellite re-alignments
Dec 5th, 2013 at 4:47pm
 
Started with Tooway on November 1st, and for a month the service has been satisfactory, with Rx SNR varying between about 10.9 and 11.7

... which, I gather, is not as high as one would like, but we are situated only 20 kms from a beam boundary, so maybe this is what we can expect.

(I know that the beam boundaries are not precise, but what I mean is that we are 20 kms from where the Tooway finder app at http://finder.tooway-instal.com/fixe/pages/index.html changes its recommendation from one beam to another.  To be precise, it recommends the green beam which includes Pisa, but if we were 20 kms further north, it would recommend the blue beam which includes Verona, Italy.)

However, on December 3rd there was over the course of a couple of hours a sudden and marked decrease in SNR, to between 9.1 and 9.6.  (Without any change in the weather).  Since then, SNR has stayed consistently in that low range.  So this morning (December 5th) I tried re-pointing the dish, but it didn't make any difference:  the best SNR I could get was about 9.6.

Then I found that the modem was having difficulty in getting back online, and in fact it was continually oscillating between trying the "correct" green beam, with SNR about 9.5, and trying the neighbouring blue beam, where it was getting SNR of 11.2.

So I went back to the 'install' stage, and selected the blue beam.  After that, the modem went online without difficulty, and SNR (using the blue beam) has now stayed consistently above 11 for several hours.

So my questions are:

1) is this kind of thing normal?

2) could it be caused by the satellite operator re-aligning the satellite, which I understand they have to do from time to time to keep everything working well?

3) if the answer to (2) is 'yes', was there a satellite re-alignment on December 3rd?

4) more generally, how often do they re-align the satellite, and can we get any warning of when they do so?

Thanks!
Frank
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europe-satellite.com
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Re: Neighbour beams and satellite re-alignments
Reply #1 - Dec 6th, 2013 at 1:00am
 
frankie wrote on Dec 5th, 2013 at 4:47pm:
Started with Tooway on November 1st, and for a month the service has been satisfactory, with Rx SNR varying between about 10.9 and 11.7

... which, I gather, is not as high as one would like, but we are situated only 20 kms from a beam boundary, so maybe this is what we can expect.

(I know that the beam boundaries are not precise, but what I mean is that we are 20 kms from where the Tooway finder app at http://finder.tooway-instal.com/fixe/pages/index.html changes its recommendation from one beam to another.  To be precise, it recommends the green beam which includes Pisa, but if we were 20 kms further north, it would recommend the blue beam which includes Verona, Italy.)

However, on December 3rd there was over the course of a couple of hours a sudden and marked decrease in SNR, to between 9.1 and 9.6.  (Without any change in the weather).  Since then, SNR has stayed consistently in that low range.  So this morning (December 5th) I tried re-pointing the dish, but it didn't make any difference:  the best SNR I could get was about 9.6.

Then I found that the modem was having difficulty in getting back online, and in fact it was continually oscillating between trying the "correct" green beam, with SNR about 9.5, and trying the neighbouring blue beam, where it was getting SNR of 11.2.

So I went back to the 'install' stage, and selected the blue beam.  After that, the modem went online without difficulty, and SNR (using the blue beam) has now stayed consistently above 11 for several hours.

So my questions are:

1) is this kind of thing normal?

2) could it be caused by the satellite operator re-aligning the satellite, which I understand they have to do from time to time to keep everything working well?

3) if the answer to (2) is 'yes', was there a satellite re-alignment on December 3rd?

4) more generally, how often do they re-align the satellite, and can we get any warning of when they do so?

Thanks!
Frank

1) No, check cable and connectors (waterproof?)
2) Hard to believe, if yes you should be back to normal.
3) You have to contact Skylogic but I don't think they will answer a question like this.
4) See above, maintenance warnings or weather related problems only.
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frankie
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Re: Neighbour beams and satellite re-alignments
Reply #2 - Dec 6th, 2013 at 3:01pm
 
Thank you for the reply.  Well, it definitely wasn't a problem with the cable, because in order to do the re-pointing I took the modem and a laptop out to the dish, and connected temporarily with a short (3 metre) length of RG59 coaxial, which made the 'cable attenuation' measurement in the modem status page go down to almost zero, but still the best SNR I could get on the 'correct' (green) beam was 9.6.

Whereas, as I mentioned, the neighbouring (blue) beam gave SNR of 11.2.

Anyway, things are now (a day later) back to 'normal', and I am getting SNR of 11.7 on the correct green beam, and SNR of 11.1 on the neighbouring blue beam.  So I have re-connected on the correct beam and will monitor the situation.

So the bottom line is that I experienced at least 2 days, possibly 3, of low SNR (in the range 9.1 to 9.6) on the correct beam, whereas the neighbouring beam was continuing to give reasonable SNR of slightly more than 11.

Can anyone suggest an explanation?  Satellite re-alignment (done gradually over the course of a couple of days) sounds like a plausible possibility to me, but this is pure uninformed guesswork.

I agree that Skylogic might not want to join in this discussion!  But Skylogic is one and we are many.  I think they should at least be interested in our feedback.

~Frank
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Re: Neighbour beams and satellite re-alignments
Reply #3 - Dec 7th, 2013 at 11:07am
 
My understanding is that the bandwidth of each tooway beam is 250 MHz. I don't know the number of active carriers in each beam. Possibly up to 6 carriers, each of 67 Mbit/s clear sky.  If there is a single power amplifier (TWTA) on the satellite per beam then if number of carriers is increased from say 1 carrier to 2 carriers then the levels may drop until transmit uplink adjustments are made at the gateway hub.

Best regards, Eric
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