[MRCA] Pondering Crystals for the BC-620 radio

[mkdorney at aol.com]

Something to ponder:  The BC 620 radio is a 2 frequency, crystal controlled FM radio operating phone  between 20.0 to 27.9 MHz FM.  CB radio frequencies are set on specific frequencies between 26.9650 MHz to 27,4050 MHz FM.   Unless I'm missing something, if the crystals are cut correctly, the BC-620 should be able to operate on 2 CB channels if the crystals are cut precisely and correctly..  Here's the rub - the crystals made for the BC - 620 operate in an oscillator circuit. Is there a formula to cut crystals for the BC-620 to have the radio work on specific CB channels ?  Crystal # o in the radio set is actually rated at 5.7067 MHz, but when installed in the oscillator circuit in the BC-620, transmits and receives on 20.0 MHz.  Crystal # 79 is actually cut for 8,3400 MHz, but when put in the oscillator circuit in the BC-620, operates on 27.9 MHz.
 
Has anybody actually had custom crystals cut for a BC-620 to allow it to work on CB Frequencies?  If so, is there a formula used to determine what frequency the crystal should be cut for?  I know that running CB frequencies isn't exactly in anybodies wheelhouse, but if this could be figured out, perhaps the BC-620 becomes a popular player in the vintage military radio world, along with perhaps other vintage radio sets.
 
Mark D.
WW2RDO
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