I've been toying around with the idea of digitizing the entire AM commercial
broadcast band and -- mainly for my own edification -- doing demodulation in
a microcontroller or DSP. Although on one hand I'd claim I can then do cool
things like AM stereo demodulation, on the other hand I do recognize such
coolness is lost in that digitizing the _entire AM band at once_ from
550-1600KHz only allows me to adjust the gain of an RF amplifier to the
point where _the sum of the signals from all the stations_ doesn't overload
an ADC. In other words, this approach will only work to pick out relatively
strong stations if I still want anything resembling a decent SNR, correct?

To get around this problem, then, I was thinking of using an NE602 mixer to
select just the station I wanted and then following its output with an
adjustable RF amp. If I go for the direct conversion approach, then, I can
follow it with a variable gain baseband amplifier and still hear the weak
stations with relatively good fideilty.

Is this a reasonable approach? Is it true that low (...to moderate?)
quality receivers can get away with just feeding an antenna's output to a
fixed gain broadband amplifier (or even just a matching/bandpass filtering
network) followed by a mixer and _then_ an adjustable gain element? (As
opposed to high quality receivers that appear to have tuned RF amplifier
front ends?)

The idea of digitizing an entire band at once seems to look far less
promising if your goal is to dig out weak stations...

Thanks,
---Joel Kolstad

(I also find it quite amusing to think I can build an evelope detector in
software to test things out prior to building fancy synchronous detection
routines!)