"Brenda Ann" ) writes:
"RadioGuy" wrote in message
...
With the proper hookup you will get a tone---and the tone will be
adjustable
in frequency depending upon operator preference.

Ah, but then it wouldn't be a totally passive receiver. The OP is looking to
use only the passive receiver, not any add-ons or external sources.


Maybe he's talking about a bit of DC bias, and kicking the diode into
oscillation. There were reports of that sort of thing happening when
"crystal radios" were still pretty important.

Likely finicky, if one can get a specific diode to oscillate, and no
it's no longer passive, but it is simpler than the obvious solution of
adding an extra beat oscillator.

Michael

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

CW, the original digital communications, may be copied, because the on-off
action would vary any noise.

Bill, K5BY

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

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?


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"starman" wrote in message
...

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?


There was a circuit, very simple, for a germanium diode receiver for the FM
broadcast band. Basically, it consisted of a large loop and variable
capacitor making up the tuned circuit, a germanium diode, a resistor, a 100
pF disc cap, and a crystal earphone. Tuning was by slope detection,
although I can't see why such a device could not be made into a ratio
detector by center tapping the coil (or making two identical coils, and
tapping between them). Also no reason that you could not listen to an
airplane's broadcasts on such a device with the loop cut to those
frequencies.

As for the law, I don't think there actually IS one, only a convention
disallowing use of radio receivers/transmitters onboard commercial flights.
The reason for this is because the local oscillator of an FM radio falls
directly in the aircraft comms band anywhere above 97.4 MHz. A crystal
radio would not interfere, and would be impossible to detect. One for such
close proximity to the transmitter could be just a small coil, instead of
the loop, and could be built into something like a pocket radio case.

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

starman ) writes:
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?

Some "crystal radios" for the aircraft band were described in the hobby
magazines thirty and so years ago. They specifically used the "it doesn't
radiate, so it's safe on an aircraft". I never saw a third party opinion
on it; clearly it is safer than borderline things that are allowed on,
but I have no idea if the rules actually specify specs, or a need to
meet specs.

The articles did say they worked well on the airplane, though what
you heard was mostly transmissions from the aircraft rather than ground.
The lack of selectivity in this case was not a consideration, since you
wanted to hear it all.

Michael