[Milsurplus] WWII Crystal Confusion

[Mike Morrow]

Alan wrote:

>... one crystal has the following marking,
> Channel 386   38.6 MHz

That one is for a BC-684 (SCR-608/628) transmitter.  
Channel frequency is 72 times the actual crystal frequency.  
Channel numbers from 270 to 389
Channel number = 10 x channel frequency in mcs.
120 channels at 0.1 mc spacing.

>The other as follows,
>Channel 36     23.6 MHz

That one is for a BC-604 (SCR-508/528) transmitter.
Channel frequency is 54 times the actual crystal frequency.
Channel numbers from 0 to 79.
Channel number = 10 x (channel frequency in mcs - 20).
80 channels at 0.1 mc spacing.

>1.- The BC-604/684 transmitters used crystals like this I think. If so, 
>what is the Multiplication factor?

See above.  Also, see 
http://www.ai.mit.edu/~sw/html/NS1W/ft-241.html
for more good info.

>2.- The BC-603/683 Rx were tunable, no crystals?

They were tunable, push-button car-radio-type channel selection.  No crystals.  Each receiver channel would be set using the crystal controlled transmitter signal:
BC-603: 20.0 to 27.9 mc,  BC-683: 27.0 to 38.9 mc.

>3.- What crystals and markings and multiplication factors were used with 
>the BC-620/659/1335?

These sets used the smaller FT-243 crystals that, IIRC, controlled only the receiver frequency (transmitter frequency was controlled by the receiver and an AFC system).  I seem to recall that for the BC-1335 and -659, you had to subtract the IF of 4.3 mc from the channel frequency, then divide by 4.0, to get the crystal frequency, but I may have that wrong and I don't have my manuals with me now.  The actual crystal frequencies ran from about 5.5 to 8.5 mcs.  The operating frequency was the channel number marked on the crystal, divided by 10.

>4.- What were the likely radios that his two crystal would be for?

See above.

73, 
Mike / KK5F