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Re: [Discuss-gnuradio] Direct Conversion vs Superheterodyne

From: David Bengtson
Subject: Re: [Discuss-gnuradio] Direct Conversion vs Superheterodyne
Date: Tue, 14 Jan 2003 22:45:01 -0500

On Tue, 14 Jan 2003 19:25:34 -0800, you wrote:

>On Tue, Jan 14, 2003 at 06:19:31PM -0500, Lisa Bengtson wrote:
>> >How is this different than a single stage supper-het?  Isn't that just
>> >mixing down to base band?  Is there something I'm missing?
>> Nope, you are not missing a thing. It's the same as a single Stage
>> Super-het, with an IF of Zero. Typically, a Super-het has a final IF
>> that isn't at DC. 
>Are you saying that most receivers detect at IF (f != 0) and not a base 
>band (f == 0)?  I was under the impression that most detectors did their 
>thing at baseband and required a final down convert from IF.

I'm familiar with at least one type of FM detector that uses a LC tank
resonant at 470 kHz to FM demodulate a 455 kHz IF, used in cheap and
Dirty pagers. I suspect that there are other demodulator types that
can demodulate a non-zero IF, although I'm getting out of my knowledge
area at this point. My main worry has been getting a signal from the
GHz range down to a few 10's of Mhz, and then I wash my hands of it. 
>> Super-Het's are pretty well understood at this point, people have been
>> hacking on them for 70 years. Direct Conversion and Undersampling have
>> some gotcha's that are not fully understood and publicized yet. That's
>> what makes them interesting.
>That's why we're talking about it.  We're geeks; it's in our nature
>to try something exotic and not fully understood, if it looks like it
>may have promise.  :)

It's all fun and games until you actually try to make one on schedule
and under a cost target. :-(


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