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

My Crystal Radio Page
Click here to download the full size of the above Circuit.

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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