I picked up the S-band filters on the post office today, and it turns out that there are indeed two different filters
1) Centre frequency 2125 MHz, Bandwidth 295 MHz (I assume 3 dB B/W)
2) Centre frequency 2375 MHz, Bandwidth 295 MHz
I tried both filters and it looks like the lower freqeuncy filter does not - to a sufficient amount - attenuate the unwanted signals, so I will use the second one .
The GSM sidebands have completely disappeared, much to my relief. (Not a trace of them in the spectrogram). I need a bit more amplification, but that is easily arranged using a second satellite TV in/line amplifier.
It looks like my theory of insufficient image rejection in the receiver is correct.
Now for some S-Band satellite signal hunting - and of course the LRO on S-Band.
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