Вот чё есть - FM Crystal Radios
copyright © 2006 by Larry J Solomon
I have heard, even from a physicist, that it is impossible to build FM crystal radios. On the other hand some experimenters claim that they have built them. This argument intrigued me to try and build an FM crystal radio, which I have done successfully. To my surprise, the result is an astounding performer, pulling in four local stations in Tucson. When connected as a receiver to a good sound system the sound fidelity is as good or better than more expensive AM radios. In fact, it sounds "high-fidelity".
This picture shows the Solomon FM Crystal Set in an acrylic display case. I made the set specifically to fit inside this case (the case came first).
My definition of a crystal radio is one that is not powered, except by the radio transmission itself and employs a crystal detector. So, it cannot have any batteries or AC power. An FM crystal radio must be able to detect and receive FM signals well enough to be heard in earphones without any such extra power.
The circuit looks identical to a classic AM crystal circuit but is even simpler to build. The components were reduced in dimension to resonate at higher frequencies. This was done by experimenting with smaller and smaller coils and capacitors. The antenna is also much reduced in size (from that of AM) to resonate at higher frequencies. The air variable capacitor I used has two trimmers in it which should be adjusted for best reception.I have found that a commonly available vernier dial and knob will fit the capacitor nicely. See end of article for a picture of the variable.
C3 is a ceramic capacitor of 18 pf, but may be anywhere from 10 to 50pf. A detected FM signal is converted to AM due to an effect called slope detection that modulates amplitude.
This FM Crystal Set works best near the transmitter (I have not tested it beyond about 10 miles). Secondly, the sound level is not very loud; a quiet room is best for listening.One must be willing to move the set around to find a location for the best reception of signals. However, in addition to listening with high impedance earphones (crystal or otherwise), the set can be connected directly to an audio amplifier's low level magnetic input which can then play amplified through a sound system at any volume -- sounds GREAT. No additional wiring or antenna is necessary (the antenna is optimized in length for FM.
L - 4 turns #18 copper or silver wire, 12mm inside diameter, tapped at 2.5 turns
Ant - 7 inches of #18 bare copper wire
C1 - 18 pf ceramic capacitor
C2 - 50 pf air variable capacitor
D - 1N34 diode or rock crystal
R - 150K resistor
I consider this set a work of art. The diode is tapped directly to the antenna. The vernier dial fits directly on the tuning capacitor. The antenna parallels the perimeter of the acrylic face plate. "Military style" #18 AWG wiring is used without any insulation. It is important to keep the components physically close together. The component specifications are the same as in circuit #2. The coil is silver rather than copper, but copper will do just as well. The coil was wrapped around a "magic marker", then slipped off and expanded. The wooden base is made from lacquered, polyurethane padouk.
I consider this to be the most elegant crystal set I have created. Yet the circuit is so ridiculously simple that some will not believe it is possible without building it themselves. No shielding is necessary, and there is no problem with hand capacitance. However, the output cable position may affect reception sensitivity.
Photos of wired circuit
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A hand is included in this photograph to show scale. Note the military style wiring, diode, and antenna. I wanted the wiring to create a modern design similar to a Mondrian painting.
This shot shows the elegance of the FM set best, I think. There is only one resistor and one fixed capacitor.
The inside of the tuning capacitor and the phono jack/output can be seen here. Can you spot the ceramic fixed capacitor here? Note the polished edge of the face plate.
A quarter-inch piece of lucite was fitted under the tuning capacitor to anchor it. Note the two tiny trimmers on the back of the tuning capacitor.
The vernier dial is large to accomodate ease of tuning, and the vernier makes it especially easy to separate stations. Two golden (brass) wood screws fix the face plate to the base. Holes for the face plate were made with special plastic drills, but ordinary drills may be used if drilled very SLOWLY. The knob is removable.
