On Sat, Jan 1, 2011 at 9:12 AM, ikjtel <[email protected]> wrote: > > 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 > > Max, Marcus, thank you very much! A lot of this is over my head right now but I'm reading up and hope to put to work some or all of your suggestions. I especially like the prospect of having a cheap but effective USB SDR. Although if I had a USB SDR I probably wouldn't even need to perform surgery on my HF allmode rig.
Also, a little more reading revealed that my rig has a third IF that operates at 455Khz and is utilized in FM and WFM modes, which may be just what I need, and what you were describing, Max. BH > > > > _______________________________________________ > Discuss-gnuradio mailing list > [email protected] > http://lists.gnu.org/mailman/listinfo/discuss-gnuradio >
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