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Crystal Radios

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SlicRic

New Member
Hi,
I am looking into building a crystal radio and AM broadcast band transmitter as a 'Set' all of the schematics show diagrams involving a coil which has to have small sections of wire exposed called 'Taps' I do not like this system and prefer to use a solid coil and havea variable capacitor somewhere, can anyone provide me with a design for such a circuit?
Thanks Mick.
 

Ross Craney

New Member
I feel that the only thing you'll hear on your xtal set will be your AM broadcast xmitter
 

stevez

Active Member
Mick - There's a couple of very good websites on crystal radios. The Xtal Society is one website that looks pretty good. Xtal is a short way of spelling crystal.

I saw a really cool project described that used an RF amplifier ahead of the crystal so that the voltage handled by the crystal was significantly greater than it would otherwise see. The author explained that this would result in greater fidelity as the crystal would be operating in a more linear way. The RF amp was vacuum tube - the high voltage was supplied by connecting 10 - 9 volt batteries.

Sounds like fun. Best of luck.
 

Dean Huster

Well-Known Member
You might find that your local radio station will blast out far more power than your own transmitter, even though it's in the same house. When I was building crystal radios back in 1965, I could get the local 1000-watt KADY in St. Charles (MO) but not the clear-channel KMOX with its 50KW in St. Louis, just over the river.

Using a battery powered RF amp is unfair as it takes the circuit out of the crystal radio category -- after all, every AM radio has a detector!

One design that keeps it "free power" uses two antennas. One long one that you tune to a strong station, rectify using a voltage doubler or tripler and then filter and use THAT voltage to power the RF or audio amplifier. A second antenna and circuit is used for the regular crystal radio portion to tune the station of desired interest.

Another design biases the diode (again, a battery, but it's being used in a different way) up so that it begins rectifying with smaller signals instead of waiting for something as big as 0.3v to break the barrier potential. Never tried a hot-carrier (Shottky) diode as they weren't around in 1965.

Whatever design you use for your crystal radio, find one with lots of tuned stages. Most simple crystal radios made using single-stage toilet paper tube coils and such don't tune well (or at all) and if you have more than one station, you can't separate them.

Dean
 

mvs sarma

Well-Known Member
You might find that your local radio station will blast out far more power than your own transmitter, even though it's in the same house. When I was building crystal radios back in 1965, I could get the local 1000-watt KADY in St. Charles (MO) but not the clear-channel KMOX with its 50KW in St. Louis, just over the river.

Using a battery powered RF amp is unfair as it takes the circuit out of the crystal radio category -- after all, every AM radio has a detector!

One design that keeps it "free power" uses two antennas. One long one that you tune to a strong station, rectify using a voltage doubler or tripler and then filter and use THAT voltage to power the RF or audio amplifier. A second antenna and circuit is used for the regular crystal radio portion to tune the station of desired interest.

Another design biases the diode (again, a battery, but it's being used in a different way) up so that it begins rectifying with smaller signals instead of waiting for something as big as 0.3v to break the barrier potential. Never tried a hot-carrier (Shottky) diode as they weren't around in 1965.

Whatever design you use for your crystal radio, find one with lots of tuned stages. Most simple crystal radios made using single-stage toilet paper tube coils and such don't tune well (or at all) and if you have more than one station, you can't separate them.

Dean
I do recall my memories of 1957, when I was made to listen to songs on a crystal radio tuning a station at Ceylon (Srilanka) while still 25 miles away a local station was available on medium wave.some sort of bigger coils and tuning air capacitors were employed.
The head phone was single and heavy, that is all I remember as I was just 12 and a student of High School education.

This makes me feel for sure, that if we are away from power and other modern disturbances, say in rural areas, even long distance reception would be possible even on crystal radio.
 
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