[Ground-station] channelized FM SDR

[Phil Karn]

On 11/1/20 18:19, Robert McGwier wrote:
> It is a real shame we can't purchase high quality FM bandstop filters.
> I have purchased some I hoped would work and they attenuated the FM
> band and much more. Next, as you well know, lots of people pretend
> every piece of crap they hook to the antenna terminal is a 50 Ohm
> resistive load at all frequencies from DC to light and doesn't crash
> the front end filtering etc with their decidedly not 50 Ohm resistive
> loads.

I've had occasional overload problems with the AM broadcast band on
MF/HF with the KiwiSDR, a 30 MHz direct-sampling receiver. Here the
cheap bandstop filters work pretty well because the background noise
levels at these low frequencies are so high that even 30 dB of
attenuation don't seem to affect overall system performance. It simply
brings the AM broadcast signals below the A/D overload level but I can
still hear them along with the ham bands on either side.

The FM broadcast band is different because noise figure actually matters
here.

Phil