On 04/22/2011 01:23 AM, m II wrote:
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It's probably been done already, but here goes:

How about making a two part receiver, one stage for the normal detection
and tuning, the other a really wide band receiver with a conversion
portion in it.

That part would collect any and all signals hitting it and convert it to
a very small dc output. That in turn could be used to power an amplifier
for the audio of stage one and then work a small speaker.

Surely there should be enough broadcast power over the entire AM band,
that, if collected and rectified, would drive a 2 inch speaker at very
modest levels.


mike

no

mV/m means roughly how much voltage is captured by a 3.3' loop. Note
that next to the antenna a huge station will produce about 2.5 to 3V in
the sampling loop. A long wire antenna would probably capture enough
Volts to drive a transformed speaker, but then you couldn't use a small
signal diode; you'd need something a little beefier.

I have used this technique to build air monitors at stations where
studio and transmitter share a location, but I always use a power amp.

http://www.fccinfo.com/CMDProEngine....97821&sHours=D