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Re: [Discuss-gnuradio] Welcome and brief update

From: John E. Perry
Subject: Re: [Discuss-gnuradio] Welcome and brief update
Date: Mon, 13 Jan 2003 13:00:04 -0500
User-agent: Mozilla/5.0 (Windows; U; Win98; en-US; rv:0.9.4) Gecko/20011019 Netscape6/6.2

Marshall White wrote:

The answer is that you must have a "tuner" that takes the signal at 107.5 MHz and 
"moves" it down
to a much lower frequency (called an IF, or intermediate frequency).

If you have a 40 MHz sampling rate, any IF less than 20 MHz should more or less 
be okay.

If you had a 400 kHz sampling rate, then your IF would have to be CENTERED at 
100 kHz.


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

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