From up toNational provided Airways companies with HRO receivers for use at airports and for airway navigation uses. The RCD provided specific airways features like squelch, relay controlled speaker selection and audio bandpass filters and single audio amplifier output sections designed for either Z ohm lines or Z ohm speakers that had internal output transformers.
How it works[ edit ] Diagram showing how a crystal detector works The contact between two dissimilar materials at the surface of the detector's semiconducting crystal forms a crude semiconductor diodewhich acts as a rectifierconducting electric current in only one direction and resisting current flowing in the other direction.
Its function was to act as a demodulatorrectifying the radio signal, converting it from alternating current to a pulsing direct currentto extract the audio signal modulation from the radio frequency carrier wave.
This diagram shows a simplified explanation of how it works: The rapid oscillations are the radio frequency carrier wave. The audio signal the sound is contained in the slow variations modulation of the size of the waves.
If this signal were applied directly to the earphone, it could not be converted to sound, because the audio excursions are the same on both sides of the axis, averaging out to zero, which would result in no net motion of the earphone's diaphragm.
B This graph shows the current through the crystal detector which is applied to the earphone and bypass capacitor.
The crystal conducts current in only one direction, stripping off the oscillations on one side of the signal, leaving a pulsing direct current whose amplitude does not average zero but varies with the audio signal. C This graph shows the current which passes through the earphone.
A bypass capacitor across the earphone terminals smooths the waveform, removing the radio frequency carrier pulses, leaving the audio signal. When this varying current passes through the earphone voice coil, it creates a varying magnetic field which pulls on the earphone diaphragm, causing it to vibrate and produce sound waves.
Circuit of a simple crystal radio. The crystal detector D is connected between the tuned circuit L,C1 and the earphone E. C2 is the bypass capacitor. Pictorial diagram from showing the circuit of a cat whisker crystal radio. This common circuit did not use a tuning capacitorbut used the capacitance of the antenna to form the tuned circuit with the coil.
Crystal radios had no amplifying components to increase the loudness of the radio signal; the sound power produced by the earphone came solely from the radio waves of the radio station being received, intercepted by the antenna.
Therefore, the sensitivity of the detector was a major factor determining the sensitivity and reception range of the receiver, motivating much research into finding sensitive detectors. In addition to its main use in crystal radios, crystal detectors were also used as radio wave detectors in scientific experiments, in which the DC output current of the detector was registered by a sensitive galvanometerand in test instruments such as wavemeters used to calibrate the frequency of radio transmitters.
Since the detector would only function when the contact was made at certain spots on the crystal surface, the contact point was almost always made adjustable. Below are the major categories of crystal detectors used during the early 20th century: Cat whisker detector[ edit ] Galena cat whisker detector from s crystal radio Cat whisker detector using iron pyrite crystal Galena detector in a cheap s crystal radio Popular form in portable radios, with the crystal protected inside a glass tube Patented by Pickard in  this was the most common type of crystal detector, mainly used with galena   but also other crystals.
It consisted of a pea-size piece of crystalline mineral in a metal holder, with its surface touched by a fine metal wire or needle the "cat whisker". Only certain sites on the crystal surface functioned as rectifying junctions. The detector consisted of two parts mounted next to each other on a flat nonconductive base: Crystal Galena crystals sold for use in crystal detectors, Poland, s A crystalline mineral formed the semiconductor side of the junction.
The most common crystal used was galena lead sulfidePbS, varieties were sold under the names "Lenzite"  and "Hertzite"   a widely occurring ore of leadalthough other crystalline minerals were also used, the more common ones were iron pyrite iron sulfide, FeS2, "fool's gold", also sold under the trade names "Pyron"  and "Ferron"    molybdenite molybdenum disulfideMoS2   and cerussite lead carbonatePbCO3  Not all specimens of a crystal would function in a detector, often several crystal pieces had to be tried to find an active one.
A rough pebble of detecting mineral about the size of a pea was mounted in a metal cup, which formed one side of the circuit.Crystal deodorants may be natural, but that doesn't mean they are aluminum free.
Questions persist about the safety of using aluminum based antiperspirants. Making a crystal radio is a good experimental project. If you want to do some more research, design experiments to answer the following questions. Prior to performing experiment, suggest a write down a hypothesis as the answer to your question.
Radio Electronics Pages.
General information. The laws regarding the use of the radiospectrum are actually fairly uniform, and established byinternational treaty, for the obvious reason that radio signals do notrespect international borders. Sir Jagadish Chandra Bose, Radio research. Bose's 60 GHz microwave apparatus at the Bose Institute, Kolkata, India.
His receiver (left) used a In , Pearson and Brattain gave priority to Bose for the use of a semi . Independent Research Project: Crystal Radio Proposal: Proposal Lab Report: Introduction The crystal radio relates to what we learned in physics because it deals with circuits, which was a key part in our course.
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