Crystal radio schematics

Posted on Feb 6, 2014

The fundamentals of crystals has not changed since this article appeared in a 1960 edition of Popular Electronics. The way they are grown, cut, and packaged has changed fairly significantly. An understanding of how they work at the atomic level has advanced significantly. The number of devices in which they are contained has increased significantly.

Crystal radio schematics
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However, except for the vacuum tubes in these oscillator circuits being replaced by transistors, nothing much has changed. An amateur radio operator, an airline pilot, a police radio dispatcher, a broadcast-station announcer. sound like a hodge-podge of job holders Maybe so, but they have at least one thing in common. All make daily use of the peculiar properties of quartz crystals - thin, glass-like plates that keep the world in tune. Crystals are found in almost all commercial and ham radio equipment, but few of their users know how they work. Before we examine the details of crystal operation, let`s take time out to define our terms. There are three important words involved: resonance, damping, and piezoelectricity. Fig. 1. In a typical oscillator circuit, turning the oscillator on develops a voltage between its cathode and grid, and this voltage shocks the crystal into vibration at its resonant frequency. The vibration in turn develops an alternating voltage across the crystal terminals, which is amplified by the tube. The LC circuit is tuned near the crystal frequency and presents a high impedance in the tube`s plate circuit. Consequently, a portion of the amplified voltage is fed back to the crystal and maintains oscillation. Fig. 4. Overtone oscillator will provide output up to 60 mc. with crystals ground for third-harmonic operation. LC circuit must be tuned to output frequency. Structurally, the piezoelectric...

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