🚀 go-pugleaf

In article <1993Jan2.200922.19977@sequent.com> washer@sequent.com (Jim "Throw it over the wall" Washer) writes:
>I have a radio shack Pro-24 crystal controlled scanner..... (yep, poor me).
>It uses a 10.7MHz IF, and says to use third overtone crystals...
>
>So, am I correct in  calculating the crystal fundamental as:
>
>F(fund)*3 + 10.7MHz == Receive Freq?
>

Ahoy, Jim!

   Actually, you won't have to work that hard at it.  Most scanner crystals
sold are assumed to be third-overtone series type.  The bit about the
third-overtone is generally assumed.

   The IF is generally irrelevant in figuring crystal frequency, provided 
you're using the radio for the frequencies it was designed for.  [There
are some "tricks" using the IF to receive out-of-band signals, but they
perform so _badly_ that one is often better off buying a new radio].

   If you check with Radio Shack for your crystals, they will have a
frequency stamped on the side indicating the frequency you'll be receiving
if you plug it into one of their radios.

   If you go to a third-party manufacturer, you'll generally only be expected
to specify what frequency you want to receive and the make/model of the radio
you'll be using it in.

   If, on the rarest of occasion, they ask what "cut" you would like on the
crystal, then you could tell them you want it optimized for third-overtone
oscillation.  However, if they ask that, they are probably talking about
high-precision crystals which they will want several hundred dollars for, 
which you don't need for scanner.

   As a rule, stay away from used crystals.  However, don't pass up any
free give-aways just because they're used!  Just don't waste your money.

Have fun with your 24!
-- 
Carter R. Bennett, Jr. - Scientist | "Oh my God!  I _AM_ a nerd!!!"
carter@scilab.lonestar.org - home  | - C. Bennett, Sept 25, 1992, after
carter@cmptrc.lonestar.org - work  | realizing he had been talking about
KI5SR          | "market availability of preconfigured Toll-House cookies."