I'm impressed with the spectrum monitor and also the NB SDR page. It is a huge help - thanks to all concerned.
I would like to know if the db scale on the WB monitor is a true reflection of the signal being transmitted.
As I type this the beacon is showing a signal about 8-9db over a noise floor of 1db.
If I have an antenna / LNB setup that allows me to see the transponder noise floor, would I expect to see a signal from the beacon that is about 8 db higher than the noise floor when viewed on my spectrum analyser? As per the BATC WB spectrum monitor.
Phil is still fine-tuning the spectrum monitor, but we think that the 8 dB above the noise indication is within one or 2 dB of the reality of what is being received at Goonhilly.
On a 1.2m dish with a consumer LNB, this is the typical SNR, because the gain of the dish does not overcome the LNB noise. A 1.8 m dish might achieve 10 dB and that is a bit nearer what is actually transmitted from the transponder. Not sure that I have seen anyone report more than 11 dB MER on the beacon - but I would be happy to be proved wrong!
I think that the Goonhilly spectrum monitor provides a fair representation of the Wideband Transponder Beacon C/N. I've attached a photo of my spectrum analyser for comparison (1.2m, Octagon LNB).
The C/N that you see on the analyser is the result of the uplink C/N AND the downlink C/N; this is what determines the overall Link Budget. With the current Beacon uplink conditions, you could have the biggest dish and lowest noise LNB and you would only see an improvement of about 3dB ie the 8dB would rise to around 11dB or so.
If anyone out there has access to a 21m dish say, then they may like to try it ! 73
he large hump on the left is the 2MS/s beacon while the smaller one on the right (~747.5MHz) is a 333KS/s signal.
the spike in the center should not be there! the “Correct IQ” feature is useless.
now I have to try to enlarge/expand the vertical scale so that I can easily read 1 dB…
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