Re: [Discuss-gnuradio] Sample audio from my FM stereo receiver

[Marcus D. Leech]

On 11/03/12 10:54 PM, Johnathan Corgan wrote:
> This is where I've run into a lot of issues.  Too much gain, the lower
> end of the dynamic range is filled with IMD.  Too little gain, the
> noise figure is too high.  It's hard to get even 12 bits of ADC
> dynamic range in the presence of strong signals.
>
>   
It's the "dirty little secret" of SDR--analog considerations continue to
be important.  Although I suppose
  with a direct-sampled 28-bit ADC running at a few Gsps, you'd have
enough dynamic range and oversampling
  to cope with anything--as long as whatever gain stages you had in
front of the ADC would remain nice and
  linear :-)

Some broadcast FM receivers (even analog ones) have a tracking filter in
the front end, to eliminate the
 IMD problem before it becomes a problem.   That eliminates the "broad
as a barn door" front-end issues.

I'm using the TVRX2, which uses the TDA18272 chip, which has a built-in
4-band band-select filter, so that
  may improve things quite a bit in terms of keeping subsequent stages
linear.



-- 
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org