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

[David I. Emery]

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."