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
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