| Journey to the Bottom of Your Rig, Radio Fundamentals explored. Original article by Houston, Long, Keating, et al, now with comments by Tom Farley. Reprinted with permission.
Pages: (1) (2) (3) (4) (5) (6) (7) (8) Modulation page // Oscillator Page
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If you'll look where I'm pointing, that's where the radio frequency is produced. That circuit is called the crystal controlled oscillator. That square tin can over there contains a sliver of quartz crystal which puts out only one frequency, determined by the thickness of the crystal.
A crystal is just what it says. It is a piece of quartz crystal (a "rock" in a can) It operates on the same principle as a tuning fork. When you hit a tuning fork, it will vibrate at a particular frequency. The tone or frequency depends on how the tuning fork is constructed. A crystal operates in a similar way. When hit with the application of electricity, the crystal will vibrate at a frequency. Depending on how the crystal is cut, the frequency will vary.
Some rigs have up to 23 crystals or more to transmit on every CB channel. Other rigs save a lot of space (and money) by using only a few crystals and running the frequencies they produce through some mixing circuits so as to get all 40 channels. Pretty fancy, huh? This circuit is called a synthesizer.
The voltage put out by a crystal vibrating is very small, a few millionths of a volt. The signal generated by the crystal gets boosted by another part of the oscillator so that it has enough voltage to drive the power amplifier. The modulator over there makes the juice in the power amplifier change with your voice. The power amplifier is where your carrier gets kicked up to that 5 watts to go out the antenna plug.
Well, here we are again at the antenna. We've kind gone all the way through this maze and come back round to the beginning. That power amplifier was the last circuit.
Back to page one
From The Big Dummy's Guide to C.B. Radio, courtesy of The Book Publishing Company P.O. Box 99,Summertown, TN 38483 (888) 260-8458, (1976). Editors: White Lightning (Albert Houston) WB4BWR, Stringbean WA4LXC (Mark Long), Minnesota Mumbler WB4KDH (Jeffrey Keating), Ratchet Jaw K4IAP (William Hershfield), Buffalo Bill WA4KCF (William Bradley) Illustrations by Mark Schlichting and Peter Hoyt.
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