High-pass filters in soundcards - an issue with I/Q-sampling?

GNU Radio
1

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

2

On Mon, Jul 14, 2008 at 04:48:29AM +0200, Hansi D?mpfle wrote:

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?

Hi Hansi,

use gr.c2f, then you can use the 2 input channels of audio_sink. Vice
verse for audio_source.

Cheers,
mb

–
Martin B.
Institut fuer Nachrichtentechnik
Universitaet Karlsruhe

http://www.int.uni-karlsruhe.de

3

2008/7/14 Martin B. [email protected]:

use gr.c2f, then you can use the 2 input channels of audio_sink. Vice
verse for audio_source.

Tnx Martin, that’s what I’m looking for.

Hansi