GSM interference not quite gone .... well - it was, really

It looks like I spoke too soon.

The interference from the GSM has re-appeared, tough not as strong as it was. After setting up some 260MHz antenna and preamp again, it came back. I may have to use a different preamplifier (tuned) for that system.

More work to do ....

*****Update : It was *not* the dreaded return of the GSM interference ....

Apparently , by adding the second amplifier (and a second receiver) in the system, I inadvertently made a loop creating humm in the system.

with less "MIC boost" at the pc sound card input the problem disappeared (only the base 50Hz and the 3rd overtone 150 Hz are visible on the spectrogram now), and I am now back to a quiet S-Band reception.

Phew !