>>
This is probably a silly idea but how about a small coil that picks up stray
rf radiation, rectify it and pump up a low leakage electrolytic, this could
be used in conjunction with the battery,
<<

Hmm.  If you're close enough to a major transmitter and you can put up a
decent antenna and protect it from lightning, etc, then it's at least
theoretically possible although rather unlikely to work in practise.

When I was a kid I had a crystal radio.  The strongest signal came from an
AM transmitter about 25 miles away that put out 50KW at 1.03MHz.  My antenna
was about a 50 foot horizontal wire strung between my window and a post
mounted to a tool shed.  This station (WBZ, Boston Massachusetts) came in
well enough to produce quite reasonable volume in the headphones.  One time
I hooked the output to an audio transformer and powered a small 3 inch
loudspeaker with it.  It wasn't very loud, but you could understand what was
being said with the speaker on the table if the room was quiet, but
otherwise you wouldn't notice it was on.  It was also useful for annoying my
brother by leaving it on at night.  He wouldn't notice it accross the room
in his bed until everything was quiet and he was trying to get to sleep.


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, olin@embedinc.com, http://www.embedinc.com

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