starman wrote in message
...
Michael Black wrote:

WShoots1 ) writes:
To go higher in frequency would require a diode capable of higher
frequency.

My first crystal set, a Philmore, used a galena detector. My second
one used an
out of spec microwave diode (1N23). G

Of course, a real problem with a "crystal radio" is that it's only got
one tuned circuit at the front end. Long before the diode becomes an
issue,
the fact that that single tuned circuit will be pretty wide as you go up
in frequency will be a significant factor. Even at AM broadcast
frequencies,
the selectivity of most "crystal radios" is marginal.

On the other hand, selectivity may not be a real issue as you move up in
frequency, since sensitivity is also an issue with "crystal radios".
They
work with local stations because those stations are relatively strong.
Move higher than 1600KHz, the top of the AM broadcast band, and most
people
will not come across local stations, so anything that is heard will be
weak,
and have to be a pretty strong signal to begin with. In that context,
selectivity may not be a real issue, since there will only be a handful
of signals that can be received anyway.

Michael

Anyone built a passive receiver for VHF or UHF? Could you listen to an
aircraft's communications as a passenger on the same plane? What does
the law say about using any aircraft receiver on a plane, whether it's
passive or active?

Yes... I remember reading a construction article circa 1959 (I think) in
Popular Electronics that used such a device to listen to aeronautical coms
within the passenger compartment. It was a basic diode detector mounted in
a pocket-sized plastic box. The antenna was a loop wrapped around the box.
I can't remember if there was an audio amplifier. Since it did not radiate
a signal it was viewed as allowable for use inside the aircraft; that was
the rationale expressed in the article back then---in a safer, tamer and
saner world! However, try it now at your own risk ;-)

I think the article even went on to suggest that you show your handicraft to
the stewardess HA! HA! HA!

RG