High SNR on TP1


Ernst Lobsiger
 

Hi All

While I read frequent complaints about low SNR nobody seems to wonder about high SNR. Since August 10th 2021 I have SNR above 15dB on a regular basis on TP1. I cannot remember such a period and I don't think there was a gust that gave my dish a lucky punch.

Regards,
Ernst


David J Taylor GM8ARV 🏴󠁧󠁢󠁳󠁣󠁴󠁿 🇪🇺
 

On 08/09/2021 09:10, Ernst Lobsiger via groups.io wrote:
Hi All
While I read frequent complaints about low SNR nobody seems to wonder about high SNR. Since August 10th 2021 I have SNR above 15dB on a regular basis on TP1. I cannot remember such a period and I don't think there was a gust that gave my dish a lucky punch.
Regards,
Ernst
Indeed, not, Ernst! No complaints from your more northerly and westerly cousins!

I gather that following all our queries about signal strength, transponder 1 is now running at its highest power level before running into non-linearity, so it has less than the normal back-off of 1.5 dB. EUMETSAT note that this may not be maintained.

Unfortunately transponder 2 cannot run like this (perhaps running continuous 16APSK affects this) and hence it is backed off about 1.4 dB from full power. I guess that if the power is turned up various intermodulation products or non-linearities will actually reduce the link margin even though the signal level is higher. AM-PM conversion and all that, plus spreading of the spectrum.

There is a suggestion that some of the degradation some of us see is due to using dishes which are too small, and hence picking up interference from other satellites. EUMETSAT's reference dishes are 180 cm which have a narrower beam-width.

Cheers,
David
--
SatSignal Software - Quality software for you
Web: https://www.satsignal.eu
Email: david-taylor@blueyonder.co.uk
Twitter: @gm8arv


James Brown
 

Very helpful. Thank you David.

JB

On 8 Sep 2021, at 09:40, David J Taylor GM8ARV 🏴󠁧󠁢󠁳󠁣󠁴󠁿 🇪🇺 via groups.io <david-taylor=blueyonder.co.uk@groups.io> wrote:

On 08/09/2021 09:10, Ernst Lobsiger via groups.io wrote:
Hi All
While I read frequent complaints about low SNR nobody seems to wonder about high SNR. Since August 10th 2021 I have SNR above 15dB on a regular basis on TP1. I cannot remember such a period and I don't think there was a gust that gave my dish a lucky punch.
Regards,
Ernst
Indeed, not, Ernst! No complaints from your more northerly and westerly cousins!

I gather that following all our queries about signal strength, transponder 1 is now running at its highest power level before running into non-linearity, so it has less than the normal back-off of 1.5 dB. EUMETSAT note that this may not be maintained.

Unfortunately transponder 2 cannot run like this (perhaps running continuous 16APSK affects this) and hence it is backed off about 1.4 dB from full power. I guess that if the power is turned up various intermodulation products or non-linearities will actually reduce the link margin even though the signal level is higher. AM-PM conversion and all that, plus spreading of the spectrum.

There is a suggestion that some of the degradation some of us see is due to using dishes which are too small, and hence picking up interference from other satellites. EUMETSAT's reference dishes are 180 cm which have a narrower beam-width.

Cheers,
David
--
SatSignal Software - Quality software for you
Web: https://www.satsignal.eu
Email: david-taylor@blueyonder.co.uk
Twitter: @gm8arv





Ferdinand Valk
 

Ernst,

 

I have recently relocated to the southwest of the country exactly during the period of the signal increase you mentioned. My current average fair weather SNR of 16.5 dB is about 1.5 dB higher than it used to be at my old place and it is difficult to say how much of that increase is attributable to a better spot within the footprint, how much to finetuning the new antenna setup and how much to upping Transponder power at the satellite. In short, the interpretation of the graph you attached of my SNR is not straightforward and may lead to wrong conclusions.

 

Cheers,

Ferdinand

 

 

From: MSG-1@groups.io On Behalf Of Ernst Lobsiger via groups.io
Sent: Wednesday, 08 September, 2021 08:11
To: MSG-1@groups.io
Subject: [MSG-1] High SNR on TP1

 

Hi All

While I read frequent complaints about low SNR nobody seems to wonder about high SNR. Since August 10th 2021 I have SNR above 15dB on a regular basis on TP1. I cannot remember such a period and I don't think there was a gust that gave my dish a lucky punch.

Regards,
Ernst


geojohnt@...
 

Hello Ernst, Ferdinand and David,

David knows this.
But I've been prodding Ops regularly for a couple of months now with my signal readings as to the reduction in SNR - and thus Link Margin a couple of months ago and the wildly volatile SNR level I had witnessed at time.

They confirmed the TP 1 SNR was showing a period of volitivity and thought it might be due to interference from 'external sources.' 
They undertook several tests but were unable to prove this fact.

Later, a couple of days was spent tweaking and checking both EUMETCast transponders by the service providers and the attached EUMETSAT graphs show quite an improvement in SNR was achieved.
However, this appears not to have been seen - or much of - by our Scottish members outside the central max power contour. 

Ops summing up is copied below

Dear John,
 
In regards to the issue of the recent continuing reduction of TP1 SNR, the attached plot shows that the link margins of transponder 1 have recovered and are now even higher than the previous average in 2020. The values are close to the all-time highs observed during the mission. It cannot be ensured that it stays at that level due to operational constraints given by EUTELSAT.
 
The average values on transponder 1 from January until June are the long term guaranteed values. For HVS-1 these values are similar to the HVS-2 link margins on the second transponder.
 
The intermittent degradation periods starting end of June could not be tracked to a specific root cause. It is considered to be caused by an interference from an unknown source.
 
We also emphasise that following the antenna size recommendations will provide enough link margin to cover such degradation, which are on the 3rd place of reasons for reception problems, after weather and reception station issues.
 
 
 
We hope the above helps.

I have seen quite a good increase in my TP 1 SNR here in SW London and now my clear sky SNR [1 m dish, Inverto Black Ultra quad LNB and an SR1 receiver] is at a diurnal max of 14.2 dB.
Which it hasn't been for many months.
And the volitivity has gone

Regards,
John

+++++++++++++++++

-----Original Message-----
From: Ferdinand Valk <fvalk@...>
To: MSG-1@groups.io
Sent: Wed, 8 Sep 2021 14:30
Subject: Re: [MSG-1] High SNR on TP1

Ernst,
 
I have recently relocated to the southwest of the country exactly during the period of the signal increase you mentioned. My current average fair weather SNR of 16.5 dB is about 1.5 dB higher than it used to be at my old place and it is difficult to say how much of that increase is attributable to a better spot within the footprint, how much to finetuning the new antenna setup and how much to upping Transponder power at the satellite. In short, the interpretation of the graph you attached of my SNR is not straightforward and may lead to wrong conclusions.
 
Cheers,
Ferdinand
 
 
From: MSG-1@groups.io On Behalf Of Ernst Lobsiger via groups.io
Sent: Wednesday, 08 September, 2021 08:11
To: MSG-1@groups.io
Subject: [MSG-1] High SNR on TP1
 
Hi All

While I read frequent complaints about low SNR nobody seems to wonder about high SNR. Since August 10th 2021 I have SNR above 15dB on a regular basis on TP1. I cannot remember such a period and I don't think there was a gust that gave my dish a lucky punch.

Regards,
Ernst


Ernst Lobsiger
 

On Wed, Sep 8, 2021 at 08:34 AM, <geojohnt@...> wrote:
However, this appears not to have been seen - or much of - by our Scottish members outside the central max power contour. 
John, David and Ferdinand,

thanks for the background info. It seems indeed that the increase of SNR is best seen on the continent.
Here are three more TC stations that show a similar TP1 SNR step I noted around early August 2021.

Regards,
Ernst