Re: [Discuss-gnuradio] ICOM 706 MKIIG as input to GNURadio

[ikjtel]

> Anybody else had any success in tapping the IQ in a receiver
> and feeding that into GNURadio?

Yes - haven't gotten into the 9-10 MHz range IF's, but I have built converters 
for 455 KHz IF's - overall they work quite well although there are some slight 
compromises in the overall system; for example I've found that the AGC action 
in the host receiver may interfere somewhat with some types of signals although 
it's not usually a severe problem.

After building several I/Q converters it was discovered that (for our 
application) it wasn't necessary to perform quadrature sampling in hardware - 
that is, it was sufficient simply to downconvert the signal to the center of 
the soundcard range and sample that conventionally using a single soundcard 
input channel.  The signal is then "converted" to the complex format entirely 
in software (setting the real components to the input values and stuffing zeros 
into the imaginary (Q) components).  This has the advantages of simplifying the 
hardware and of freeing up one of the two soundcard input channels.

It would no doubt be straightforward to extend these ideas to the 9-10 MHz 
IF's.  One thing though is that there's perhaps 50-60 dB more signal available 
to work with after the 455 KHz IF amp chain has done its work.  So if you tap 
into the 9-10 MHz IF you may be looking at building up a relatively significant 
amount of RF gain yourself...

Here are links to a couple of my pages containing schematic and other diagrams, 
and application notes:

http://www.lightlink.com/mhp/lsm/
http://www.lightlink.com/mhp/iq/

Good luck

Max