My Crystal Radio Page

Posted on Feb 6, 2014

Crystal radios require no outside sources of power to operate, just the radio waves themselves. The first crystal set I built was a `variometer` radio. In this design, one larger coil slides over a smaller coil to change the coil`s inductance, eliminating the need for avariable capacitor. The radio I`m building has two smaller coils, making it more selective ( ). I got the design from the

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May 1995 issue of Popular Electronics. The coil forms are made from PVC pipe. The smaller, longer coil which holds the two smaller coils is 8 inches long and 1 inch inside diameter. The shorter, larger coil which slides over the other pipe is 3 inches long and 1. 5 inches inside diameter. The other components are installed using a long terminal strip. At first the radio didn`t work because the detector diode, which should be a 1N34 germanium diode, was a Zener diode. Luckily, someone sent me some 1N34A germanium diodes, and now it works fine. Since I live in a "fringe" area for AM signals and my only set of high-impedance headphones has an intermittent connection in the "junction box" where the headphone cord is split to the two `phones, I`ve added an onboard one-transistor amplifier, whose design I found in the Boys Second Book of Radio and Electronics. Unfortunately, it has some problems. When using a crystal earphone as a microphone, the output is soft and unintelligible. The problem could lie with the transistor, since I`m using a 2N217 (ECG102A) when the original circuit calls for a CK722 (ECG102). The ECG102A is a more rugged version of the ECG102, but the voltages are different. Reducing the bias( ) resistor from. 39 Meg to 27K and doubling the voltage from 3V to 6V hasn`t made a difference. A schematic for both can be found below. My second crystal radio is a much-simpler "slider" set. This type of crystal set uses...

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