[R-390] Balanced input on higher bands correction

[Jacques Fortin]

Hello Tisha,
When you wrote: 
The on-off action of the crystal heater will cause the beat frequency to
swing up and down, sometimes as much as a hundred Hz or so. I can see why
RTTY operators would spend their entire military careers sitting in some
shelter, tweaking that adjustment for a couple of years.
(insanity may be the end result).

Well, I agree with that, (already experienced it, btw) but I believe that
the easiest solution is to turn OFF the heaters, unless the radio is
operated in sub-zero temperatures...

73, Jacques, VE2JFE in Montreal