Crystals with higher frequencies than about 30 MHz are almost exclusively overtone crystals. Such a crystal is intended to be used on an odd multiple of it’s fundamental frequency. Unfortunately, the crystal doesn’t want to resonate on it’s overtone frequency voluntarily, the oscillator circuit needs to force the correct overtone. For a little 2m band […]
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There are tons of circuits for listening devices available on the internet. For the most part, they all have in common that they are virtually useless. This article shows how to build a reliable, small and inexpensive listening device using a PLL clock multiplier and a standard crystal. Most audio listening devices, also called spy […]
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