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 _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
