[Discuss-gnuradio] high-pass filters in soundcards - an issue with I/Q-sampling?

[Hansi Dämpfle]

Hello,

I'm trying to go the poor man's approach to gnuradio with a soundcard attached to the IF of my receiver. I will mod my receiver with a 10.7MHz IF-output and feed it into a tayloe-mixer clocked also at 10.7MHz. It will output two 90 deg phase shifted signals at the baseband to the stereo-input of my 96kHz-soundcard. Thus, gnuradio should see a 96kHz wide band.

One of my concerns is the high-pass filter in the soundcard's input stage, cutting below 10Hz, according to the datasheet. When receiving a signal exactly a the IF frequency, at least in theory, both I/Q-outputs should stay at a constant DC-level which the soundcard can't read. Is this a real problem? I mean all of the signals we'd like to receive are modulated at at least some Hz, so it wouldn't matter? Of course I could always tune the receiver to some kHz above/below to cope with that. Still, it would be nice to use the whole 96kHz range.

Another question: I browsed the source of the soundcard sources/sinks. There seems to be no special complex input module with two channels, is there an easy way to do that with the existing blocks?

TIA,

Hansi