Re: [Discuss-gnuradio] Real-only direct-conversion

[Marcus D. Leech]

On 02/27/2011 06:41 PM, Moeller wrote:
> A real valued zero-IF "universal" (modulation independent) receiver does not 
> exist.
> I think you have the a demodulating receiver in mind that relies on
> symmetry in the baseband spectrum, like for AM. In this concept, "baseband"
> is the real valued audio baseband. For digital modulations it doesn't make 
> sense.
> The real valued representation with IF at half of the one-sided signal bandwidth
> can be called "real baseband", in contrast to the "complex baseband".
> Same data size, same content, same bandwidth, just shifted in spectrum.
Yup, that's pretty much what I said in my initial post on the subject.  
The 1940s-era direct-conversion
  receivers were designed specifically for things like AM, where the 
+/- frequency ambiguity didn't
  matter.

Yup, placing the IF at Fs/4 makes sense in that you can later do a 
Hilbert transform and convert to complex.
  But if the IF is at zero, you lose.




--
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org