[GreenKeys] Heath HG-10 VFO with FSK modification

[Harold Hallikainen]

On Tue, November 30, 2021 2:28 pm, Roy Morgan wrote:
> My Heath HG-10 is out of storage for restoration. It has both a small AC
> supply built in (good), and what appears to be a circuit to FSK modulate
> the oscillator (May not be useful).
>
> As I remember, it would switch a teensy bit of of capacitance on and off
> in parallel with the VFO tank circuit to shift the VFO frequency. There is
> a 2.5 mH choke, a diode, resistors and caps. (The terminal-strip mounted
> thing is disconnected from the rest of the VFO.)
>
> Can anyone point me to the details of this early FSK modification?
>
> (I expect to do real audio FSK with the Dovetron and Kenwood 440 and 940
> transceivers in SSB mode, though they do have switching level TTY inputs
> that would work. )
>
> Roy Morgan
> K1LKY Western Mass
> K1LKY68 at gmail.com


Attached is the circuit from my 1966 handbook. I added it to a Viking
Ranger to get on RTTY in 1969 or so. The circuit in the VFO is probably
this circuit.

Harold
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