Crystals

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Caddop22

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Huntsville, Al.
I have a question in regards to crystals in older scanners.

When I was a young buck my Grandfather had an old Bearcat scanner and it required crystals to pick up frequencies. I can remember him taking it to a shop (not Radio Shack) to have crystals put in it. I have often wondered how these crystals made the scanner work. Because of his love of the hobby, I also love the hobby of scanning. It was an 8 channel scanner with what I would call dip switches under each light, push it up the "bank" was on, push it down it was off. Sorry to say I dont have the old scanner today. He did leave me, upon his death, a Uniden BC210XLT, I still have it and love it.

But to the point, I think about that old scanner and wonder how crystals made it work? I hope some of you guru's can help me with this.

Any input is much appreciated.

Ken
 

kb2vxa

Completely Banned for the Greater Good
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Point Pleasant Beach, N.J.
Hi Cad and all,

They weren't DIP switches, they were slide switches. (DIP, dual inline package, same as an IC.) Usually the lights were incandescent pilot lamps, LEDs came along very near the end of crystals. There were no banks, no memories, only a handful of individual channel oscillators scanned by a primitive scanning circuit.

An oscillator is a high frequency feedback device that produces a signal that mixes with the one coming in from the antenna and converts it to an intermediate frequency for amplification. An IF amplifier has a high degree of selectivity which blocks out signals on adjacent channels so you only hear one at a time. A crystal is just that, a sliver cut from a quartz crystal. When current is applied it vibrates at a specific frequency much like a tuning fork only at radio frequencies. Like a tuning fork it is extremely stable over a wide range of conditions so the oscillator frequency stays locked in. Modern scanners still use a master reference crystal oscillator to keep the channel frequency synthesizer locked in.

There, now you don't have to ask the Wookie Pedia. (Hmmm, Chewbacca's baby?)
 
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