Re: High SNR on TP1


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
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