Thanks for the responses so far...

The idea of digitizing the entire AM band would be a lot more appealing if
someone made one of those small serial interface ADCs that had a sample rate
in the 3-4MSps range. The best I've found so far is a 1.75MSps from Analog
Devices (AD7470, a 10 bit ADC), which -- even restricting the AM band to the
'traditional' 550-1550kHz instead of the slightly expanded 500?-1710kHz --
obviously isn't adequate to sample the entire 1MHz spectrum.

Hence I think I'm going to try an approach along the lines of a
micrcontroller's PWM output feeding a Linear Tech. LTC1799 square wave
oscillator, filtering its harmonics a bit, feeding it to an NE602A mixer
followed by a (means yet to be determined) adjustable gain IF amp, and then
the ADC on the microcontroller. For the audio output I the TI TLV320DAC23
is a high quality stereo DAC with built in 100mW audio amplifiers and serial
microcontroller connectivity.

Of course this is all going to have to fit into an Altoid's tin, right? :-)

---Joel Kolstad