[Milsurplus] ARC-type-12 Transmitter on 2M FM- It's Easy.

[David Stinson]

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(  First things first-
If you want to use a type-12 transmitter on 2-meters,
you need a good antenna.  The type-12 transmitters,
when feed directly into a non-reactive 50-ohm load,
have a nasty 72 MC bump out of the final.
A resonant antenna attenuates this.  You could also
fix it with a simple LC band-stop filter.)
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Here's how to FM a type-12 transmitter
without "boogering" it up:  Move two wires.

http://home.netcom.com/~arc5/ARC-type-12/type12fm1.JPG

You stop modulating the PA and start modulating
the crystal oscillator.  With my carbon mic,
it pulls the crystal enough to swing the carrier a nice 
+/- 4 KC.
Audio isn't great and there's still an AM componant,
but it's useable and a fair trade-off for such an easy 
fix.
While the posted diagram is for a T-11A and
there are some minor differences in wiring between
the various transmitter models, the idea is simple
and the same in each case. The change can be made
at the base of the little modulation transformer.

I also introduced some IF regeneration in the receiver,
which "tightened" it up and allowed better
slope-detection of FM, but that's for another time.

73 Dave AB5S