Origin and type
The "stone radio" originated from the early geophone components that were directly made of natural ore. The ore commonly used is pyrite crystals. When in use, a metal probe is used to contact a point the size of a needle tip of the ore, and the contact point on the ore can be adjusted to find a contact point with a semiconductor effect. Using the semiconductor effect at this point, the amplitude-modulated radio wave is detected to obtain an audio signal. This kind of radio is named "Mineral Radio".
The mineral radio is the simplest of all radio receiving equipment, unless it is quite close to the radio, the erection of its antenna and ground wire is very elegant.
When the transistor was invented, radio enthusiasts replaced ore with germanium diodes. Old radio enthusiasts in China who have played with ore machines should remember the nostalgic diode model 2AP9.
Simple mineral radio can consist of only one coil, variable capacitor, detector and earphones. Because there is only one tuning loop, it is called "single-circuit mineral radio". Such a machine is in use A good line of heaven and earth can accept local or a little farther radio stations, but the ability to separate radio stations (selectivity) is very poor, and there will often be "pitch", that is, two or more radio stations ring together.
In addition to this simple form, there can also be two or even three-circuit mineral radios to improve selectivity, but there is no major improvement in volume. There is also a new type of MOSFET for detection, which can obtain a voltage drop close to 0 volts. This component has an excellent detection effect for crystal radios.
A good crystal radio requires: excellent antenna and ground cables, high-Q coils and variable capacitors, low forward voltage drop detectors, sensitive and well-matched headphones.
Advantages and Disadvantages
Advantages
No power required, energy saving and environmental protection.
It can be used to test the efficiency of antenna or ground wire.
The ore machine is very attractive and can be used to guide beginners and children into the world of radio, broadcasting and DIY.
The route is simple and easy to make.
Connect the amplifier, you can listen to the best sound quality AM broadcast.
Disadvantages
Low volume
It takes a long time (five Six meters) antenna. The ground wire is also needed.
Production method
Material
1. A base plate or a case (this can be used or not, depending on whether you want to Keep the work better);
2. A skeleton (used to wind the coil, you can use a toilet paper tube);
3. A variable capacitor;
< p>4. An ordinary capacitor (2200 picofarads);5. A high-impedance earphone (note that high-impedance must be high-impedance! Otherwise, there will be no sound, you can use ceramic speakers);< /p>
6. An ore (used for detection, it is difficult to buy, you can try 2AP9, 1N60 these two diodes);
7. A lot of wires;
8. Some enameled wires (can be removed from used coil ballasts and transformers).
Steps
The first step: use enameled wire to wind a coil on the paper tube, 90 turns, you can drill an eye at the head and tail, pass the wire through, and stick it with tape Good. Then carefully remove the paint from the enameled wire, which can be sanded.
Step 2: Connect the variable capacitor to its two sides. Make sure to determine the two poles of the capacitor. Don’t be wrong. If you have a multimeter, it’s best to measure it. The two poles of the capacitor are the ones with infinite mutual resistance. It can be soldered with an electric soldering iron and rosin solder to make it stronger.
Step 3: Connect any pole of the diode to any pole of the variable capacitor connected to the coil.
Step 4: Connect the high-impedance headphones to the other pole of the diode and the other pole of the variable capacitor (the first stage without the diode).
Step 4: Connect capacitors to the two poles of the high-impedance headphones, the 2200 picofarad.
Step 5: Connect the antenna to the place where the variable capacitor, diode, and coil are connected, which is a piece of wire. The longer the better, the more stations you receive, and the shortest is two meters. Connect the ground wire where the variable capacitor, high-impedance earphone and coil are connected.
Step 6: If you live in a building, connect the ground wire to heating pipes, water pipes, etc., and mount the antenna outdoors. If it is a bungalow, bury the ground wire In the ground, you can first insert a section of water pipe into the ground, bury it half a meter deep, then connect the ground wire and then try to raise the antenna as high as possible.
Step 7: Put on the headphones for a trial listening, turn the variable capacitor, and listen to whether there is a radio station.
Composition
The rock radio is a simple radio receiver consisting of a long wire antenna, a tuner and a detector for selecting the signal frequency. The detector can use "ore", can also use detector diode, can also use germanium high frequency triode detector.
Spy
It is said that the rock radio may still be used by spies. The rock radio does not have an oscillator, so the anti-spy organization cannot detect the frequency being monitored.