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

[Matt Blaze]

David,

Thanks -- I think you've explained it!  I just noticed that the PR 100 audio recorder creates stereo WAV files, and when in IQ demod mode the the left and right channels are indeed different.  I'll have to do a bit of playing to see if I can interpret them as analog I and Q.

Thanks again for the careful explanation -- it didn't occur to me that the receiver had a 2 channel audio out stream.  I'll bet your explanation is correct.

Best,

-matt


On Feb 18, 2012, at 1:02 AM, David I. Emery wrote:

> On Fri, Feb 17, 2012 at 11:30:02PM -0500, Matt Blaze wrote:
> 
>> 
> 
>> OK, I understand the principles of IQ data, and I've managed to parse
>> the R&S IQ data format, so all is good there.  But the receiver ALSO has
>> an "IQ" demodulation mode.  And I can't for the life of me figure out
>> what it's for, what it does, or what the audio actually is.  It seems to
>> inject a BFO, but it's neither FM nor AM. >  > Any idea what this mode
>> is?  The manual is of sadly little help.
> 
> 	Sounds from your description (don't own the radio, so I cannot
> comment from personal experience) that it must be analog baseband I or Q
> output, effectively what one would see if one fed the sample stream from
> its digital I or Q into a D/A...
> 
> 	It would make a little bit more sense if there was a "stereo" or
> two channel output of this as intrinsically it is complex... and not
> representable in a single scalar voltage.
> 
> 	I would, indeed, expect it would sound and act very much like a
> classic BFO and product detector centered on the tuned frequency of the
> radio because ... well ... it (for a ideal product detector) WOULD be
> what one thinks of as "I" as an analog signal.   And if there are two
> channels one would expect the BFO to be in precise phase quadrature for
> them making them analog I and Q outputs.
> 
> 	What kind of low pass filtering or other processing they apply
> to this output pair is unclear... obviously classically one might wish
> to low pass filter to provide some effective bandwidth for listening or 
> external processing rather than always passing all the energy up to to
> +-250 KHz away from the center of the tuned channel.   And indeed I
> would  expect that output to probably be after IF selectivity filtering
> and AGC and manual gain control whereas the digital I and Q for spectrum
> capture might more logically be before both.   But that somewhat depends
> on the intent of the output.
> 
> 	I presume these two outputs are probably provided for attaching 
> external signal processing or display devices that want analog I and Q
> input or at least are available as a audio monitoring option so one can
> check to see what the radio is hearing seen from this perspective.
> 
> 	Not clear to me that using them to just listen with ones ears to
> most signals would be all that useful, though if the radio has the
> ability to phase lock to an AM carrier, the I output would be
> synchronously demodulated AM which is a standard mode of demodulating AM
> that can produce better results on fading signals than classic envelope
> detection.
> 
> -- 
>  Dave Emery N1PRE/AE, die at dieconsulting.com  DIE Consulting, Weston, Mass 02493
> "An empty zombie mind with a forlorn barely readable weatherbeaten
> 'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
> celebration of what could have been, but wasn't and is not to be now either."
>