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[Discuss-gnuradio] Direct Conversion vs Superheterodyne

From: Tanner Lovelace
Subject: [Discuss-gnuradio] Direct Conversion vs Superheterodyne
Date: 13 Jan 2003 13:33:34 -0500

Sorry about the previous message.  Apparently the mailing list software
doesn't like PGP signed e-mail. :-(

On Mon, 2003-01-13 at 13:00, John E. Perry wrote:

> Why does everyone insist on using an if?  I seem to recall from my radio 
> classes (admittedly quite a few years ago) that direct-to-baseband IQ 
> conversion keeps all the modulation information present in the signal.  
> For all voice and program broadcast signals the bandwidth is well within 
> even low-end PC sound cards.  Phase-locked loops are not trivial, but 
> neither are they hard, to build. Essentially all common signals except 
> hi-fi FM and video signals could be decoded in practically any low-end 
> PC, couldn't they?
> What am I not understanding?
> John Perry

Well, admittedly my radio knowledge isn't as much as it should be, but
from what I understand, the main reason for superhet designs was that
it was easier to process signals at a fixed frequency than over a 
range of frequencies.  While this may be true in analog, it's entirely
possible that direct conversion would be better for an SDR.  In
fact, I was just looking at direct conversion circuits last night
in the ARRL Handbook and wondering this very thing.  Perhaps someone
with better knowledge could speak about this?

Tanner Lovelace
Tanner Lovelace | lovelace(at)wayfarer.org | http://wtl.wayfarer.org/
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