Occasionally I will be publishing articles associated with my dealings with radio in the past including when I was a "rig doctor". For several years of my life I used to repair and service radio equipment especially CB's. I used to have a CB customer called Henry (not his real name) how had a passionate dislike for a breaker that used UK CB Ch31 called Clive (not his real name). Henry wanted to wind up Clive and asked me if I could come out with a "jamming" device. Since cheap CB walkie talkies that were very common in the 80's often had crystals for Ch30, I decided to build a jammer with this crystal. I soldered the crystal into a very small oscillator board powered by a 9 volt PP3 battery. This was installed inside a cigarette packet with a short piece of wire to send out a small scale signal and was hidden up a tree by Henry very near Clive's antenna.
So you may be wonder how this worked? Very simply the crystal oscillator board was retuned from 27.89125 to 27.90025 MHz. Channel 31 is on 27.90125 MHz. So when ever someone was speaking to Clive on Ch31, the different between the two frequencies would produce an 1 kHz audio whistle (middle of human hearing spectrum) on Clive's receive. (As 27.90125 minus 27.90025 = .001 MHz = 1 kHz.) This is known technically as the Heterodyne Principle. But in reality no CB transmitter is never bang on frequency so the whistle will vary in pitch, depending on who was talking to Clive.
Well the feedback I got was that this was driving Clive bonkers. He had this mysterious interference that no one else could hear (due to the fact that the jammer was very low powered). He even got the local electricity provider (known then as SWEB) out to check the "lines" for interference. Luckily for Clive the battery went flat after a few weeks, and the interference "magically" disappeared ;-)
73's from Dave the Pixie
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