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Rádio Galena – The Crystal Radio – The Beginning of the Age of Semiconductors

The Home of Galena was the era of Semiconductors, one of the first semiconductor used by man, galena lead ore is most abundant in nature, also called lead sulfide, it contains 86,6% of chumbo e 13,4% sulfur. This semiconductor, been used for a long time due to their high efficiency in the detection of radio waves, being widely used in building homemade receptors during World War.

Cristal de galena

The crystal galena was soon replaced by semiconductor silicon germanium, and subsequently, now call “radio galena” radios having the same circuit radios galena, but because of the difficulty of finding the crystal galena he is replaced by germanium diode.

O Radio Galena

The Galena radio is also called ” radio receivers without power “, crystal radio, receiver mustache cat, etc.. It is the simplest radio receiver, popular in the early years of radio, returning to the peak in the second war. It needs no battery or power supply and operates from the energy of radio waves picked up by your antenna, um longo fio.

The name of Radio Crystal comes from its main component, known as crystal detector , originally made with a piece of galena. But various types of detectors were used, in the second war was widely used razor blade, is currently used silicon or germanium diodes.

The rectifying property of crystals was discovered by Karl Ferdinand Braun in 1874, but only in 1904 the crystal detectors have been used in radio receivers. The radio crystal was the first type of radio receiver widely used and polarized, Main used during the era of telegraphy without fio.Vendido the millions or home made in the decade of 20, this radio was cheap and reliable, thus making it accessible to the entire population radio. Since the factory radios were very expensive.

Newspapers and magazines published articles about how to build a crystal radio with common household items. To minimize costs, many of the schemes suggested winding the tuning coil on empty cardboard containers, as boxes oat, which has become a common basis for homemade radios.

In the decade of 40, me during the war, radios were strictly prohibited, the Germans had to switch radio equipment, that could detect local oscillator super-heterodyne receivers. Have the crest radios that do not use local oscillators, can not be detected in this way. Some soldiers made a crystal radio from a coil made of wire recovered, a sheet of rusty razor and a piece of pencil lead.

radio de trincheira

The operation was simple, a pin lightly pressed against the graphite blue spots (or rust stains) Oxidation of the blade, they formed what is called point-contact diode and the rectified signal could be heard on headphones. The idea spread across the beachhead, to other parts of the war, and culture popular.Este radio crystal was nicknamed Fox Hole Radio ( radio trench).


An easy-to radio

The radio crystal is a radio that can be handmade, within seconds and with low cost parts found in any junk. Basically a radio crystal consists of a wire antenna, a tuner coil of copper wire, capacitor, a detector and headphones.

A antena

The antenna crystal radio is the most critical point, since it has to have the greatest possible length, is the length of the antenna will cause the radio galena receive radio signals. It is a single-wire antenna, ie has only one wire. There is no ideal size, testing can only know the size needed, but we can start with the big cities 20 mts. Since there is no signal amplifier to listen to the radio weaker, should be heard on the radio with earphones sensitive, Glass type fones.

By lowering the price of commercial radios crystal radios were replaced by the first amplifying receivers, who wore valves Audions , and became obsolete for commercial use. However, they continued to be built by hobbyists and amateurs electronic. Currently there are a variety of teaching and educational kits.

Another advantage of crystal radios is that it can get almost any frequency, from the 20 kHz transmitters telegraphy spark-gap to the highest amplitude modulated to transmit, crystal radio can only demodulate amplitude modulation. Most schemes available on the Internet are designed to receive AM broadcast, some receive the band shortwave 49 meters, mas only strong signals.

The Ground

The wire antennas used with crystal receivers are monopole antennas which develop their output voltage with respect to ground. They require a feedback circuit connected to ground (land) so that the current from the antenna, pass through the receiver, and flow into the ground. The ground wire can be connected to a water pipe iron, or metal stake driven into the ground.

A good ground is more important for the receiver crystal than for current receivers, because the crystal radio have low input impedance, just to transfer energy efficiently from the antenna. Earthing of low resistance (preferably below 25 AZ) is necessary because any resistance in the ground antenna feed dissipates.

It is not advisable, but you can use the land taken, If your outlet does not have land, but is 127 Volts, Neon lamp with a holding in one of the poles, you play with the other pole of the bulb in the socket hole. When the light turns, this will be the live outlet, when light is not the land, because that is what you will connect the ground radio galena. No shock hazard, since the Neon Lamp no current flows, take the test grounding your body, If you are isolated lamp will not light.

A sintonia

The crystal radio tuner circuit consisting of a coil and a capacitor, the electrical charge flows rapidly and backward between the plates of the capacitor through the coil, oscillating frequency of the radio signal. The frequency of the station received is the resonant frequency of the tuned circuit, determined by the capacitance of the capacitor and the inductance of the coil.

The detector

In the old detectors, a thin metal wire with an adjustable arm touches the surface of a mineral crystal semiconductor. This forms a crude unstable semiconductor diode ( Schottky diodes ), allowing current to flow better in one direction than in the opposite. Other sensors may be used as the razor in the above mentioned radio trench and germanium diodes and finally the current silicon diodes.


The Headphones

The requirements for a good headphones to be used in crystal radios are different from ear earphones used with modern audio equipment. They have to be efficient at converting energy from the electrical signal to sound waves, while most modern ear headphones are designed to be efficient at reproducing all frequencies of sound.

Ceramic Phone
Ceramic Phone – Photos: Ebay.com

The early earphones used in crystal radios had iron diaphragm which functioned similarly to speakers . Each earpiece contained a magnet coils of wire to form an electromagnet , with poles near a steel diaphragm. When the audio signal from the radio passed through the electromagnet windings, creating a variation of the magnetic field which moved the diaphragm, to vibrate. The vibrations of the diaphragm pushed and pulled in the air in front of him, creating sound waves.

Modern crystal devices use headphones crystal piezoelectric, which are much less sensitive and also. They consist of a piezoelectric crystal with electrodes attached to each side, a diaphragm bonded to . When the audio signal from the radio unit is applied to the electrodes, cause the crystal to vibrate, vibrating diaphragm.

Headphones are designed as crystal earphones that plug directly into the ear canal, coupling the sound more efficiently to the eardrum. Their resistance is much higher, reaching Megohm, thus the tuned circuit increasing the selectivity of the receiver.

The low impedance (8 AZ) modern ear headphones can not be used without modification in crystal radio, because the receiver does not produce enough current to generate sounds with it. An audio transformer with a higher impedance can partially remedy this problem.

Make Your House in Galena Radio

How to make Crystal Radio Project 1

Radio galena

Components and Materials for the construction of radio galena:

Wood base 25cm x 25cm
Canudo or plastic pipe, paperboard, PVC or any insulating material, of 15 inches long by 3 inches in diameter.
45 meters of enamelled copper wire, any thickness.
Headset Simple, these small radios that accompany cell, The headphones are the ideal crystal.
1 ceramic capacitors 250 pF
1 ceramic capacitors 100 pF
1 germanium diode 1N60 or equivalent
15 Bedbugs metal

Adhesive tape
Lixa us

Radio Galena

In the construction of the antenna is recommended to use approximately 20m wire taut, which must be at least 3 acimas meters of buildings trees, the ends of the antenna must have insulating, which can give made of PVC pipe. At one end of the antenna must be sanded and connected to one end of the coil.

The coil winding and build up 100 turns of enamelled copper wire (28 or 30 AWG) no insulating tube, , enrrolamento the wire should be fine one leaning on the other, without superposition. The first and the last lap must be attached to the tube with tape, leaving a surplus of 20cm wire at each end. To take the enamel wire, sand up the ends or use a lighter to clean them. Sand also about l cm in width along the entire length of the coil, because this track will serve to make electrical contact, varying up the number of laps remaining connected to the receiver, this item will make the change frequency , in other words, a Sintonia.


The connection to the land can be made through the plumbing of your home, if metallic, or by a piece of iron stuck to the floor. The capacitor 250 pF should be placed in parallel with the coil and one of its terminals to be connected to ground.

The free end of this wire should be leaning on the sanded winding, can go from end to end, this thread is called cursor. With this, can be introduced into the circuit a variable number of turns of the coil, also varying the impedance and frequency.

Diode should have already connected between the capacitors as shown in Figure, the capacitor 100 pF must have a terminal connected to the diode and earphone, and the other the Earth. The connections must be laid on wooden base through bedbugs, except the free end , the cursor coil, which can be attached to the coil by a piece of tape.

Place the headset in the ear and scroll slowly and carefully with the cursor part sanded coil winding, looking tune the medium wave station site.

Radio Crystal home

Project 2

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