[Premium-Rx] R&S PR100 IQ demodulation mode?

[Matt Blaze]

On Feb 19, 2012, at 4:34 PM, Charles P. Steinmetz wrote:

> matt wrote:
> 
>> I have software to process the raw (undemodulated) I-Q IF 
>> output.  I'm trying to figure out what the IQ demodulation mode 
>> itself is actually doing.
> 
> I don't know what your particular software does, but given I and Q 
> signals, you can derive all of the various forms of modulation with 
> different processing (i.e., by implementing different mathematical 
> algorithms in either the digital or the analog domain).  That's the 
> beauty and power of IQ systems.  See Experimental Methods in RF 
> Design, Chapter 9, for an accessible discussion (and some math) 
> regarding the use of I and Q signals to recover one or the other 
> sideband.  (This is what "phasing" SSB rigs do.)
> 
> Some hams like to listen to baseband I and Q signals binaurally in 
> stereo headphones (I in one ear and Q in the other -- see above 
> reference at Section 9-5).
> 
> Best regards,
> 
> Charles
> 
> 

Hi Charles,

Thanks for the reply.  I should clarify that I understand the principles of DSPs and what I/Q data is, and have written software that can demodulate FM, etc from the PR100 IQ data stream.  It's the audio output by the PR100's IQ *demodulation* mode that I'm trying to figure out.  It sounds from what you're saying that this may simply be an audio version of the raw IQ data, sent through a D/A converter (or recorded to a WAV file).  I'll definitely get a copy of that ARRL book.

I hope that's what's going on here, since that would allow me to recover the actual IQ data from the "demodulated" IQ audio stream / wav file.  The PR100 wav files are preferable for my purposes to the IQ files, because the PR100 can be configured to pause audio recording when no signal is over the squelch threshold (but the IQ is recorded continuously, whether a signal is present or not).  This will make capturing and analyzing infrequent signals much easier.

Thanks again

-matt