"Dale Parfitt" wrote in message
...

Keith wrote:

I have a Johnson Ranger linked to a Johnson 6n2 Transmitter. The owners
manual says it can do FM.
How do I set that up. The owners manual doesn't have much info on this.
Just says that I need a FM-VFO.
I have the standard VFO that hooks into the 6n2, but that is all the
info
that I have.
Thanks in advance.
Keith

Hi Keith,
Although I have not used this particular VFO ( had the TX), the common
scheme
back then was to plug the mic into the VFO- which contained a mic preamp
and
thus FM the VFO.

Dale W4OP

The Turner +2 desk mikes are great for this use: the mike has a preamp
builtin to it, and you can hook it up directly to the varicap circuit.

However, there is a "gotcha": with the transmit switch open, the mike puts
it's preamp battery voltage out on the audio line, and it can forward-bias
your varicap, thus destroying it. You'll need a blocking cap on the input to
the varicap circuit to prevent any voltage on the mike line from damaging
the varicap diode: this is a good practice no matter what mike or preamp you
use.

BTW, most "FM" rigs are actually phase-modulated, so many receivers have
deemphasis filters in them to compensate for the 6DB/octave tonal bias of
phase-modulated rigs. Since a varicap across a VFO coil will produce "true"
FM, you might have to precompensate the audio so that it doesn't sound too
"basey" in some receivers.

HTH.

Bill