[Heathkit] HG-10 -VFO power supply, DX-60B

[Tom NØJMY - AAR7FV]

I agree with Bob McGraw wholeheartedly on going the relay route for T/R .

Lacking a Dow-key, I made a real simple time-sequential TR switch once 
by using two small RS 12V 4PDT relays with their coils in series.

One was used for switching the antenna, the vfo key, and a high 
resistance (actually variable) mute line to the receiver. It's coil was 
shunted by a silicon diode which allowed it to close more or less 
immediately on "make," but caused it to stay closed for a small space of 
time after "break" 

The other relay for keying the xmtr had a small electrolytic cap across 
its coil leads which delayed its contacts from closing immediately on 
make, yet allowed them to open before the antenna/vfo/mute relay did 
likewise.  No backwave, no suck-out, no TVI and the antenna is cold 
switched.

If you can, look in the 1982 edition of Hints and Kinks compendium for a 
slightly more elegant but virtually identical set-up by W6RSP in chapter 
4.  Or if someone can track it down on their QST CD's from the late 70's 
- early 80's time frame, under the title "Simple CW QSK".  The H&K 
version used Sigma relays which 'RSP claimed supported QSK in excess of 
45 wpm. (!)  My little Radio Shack units showed no signs of any problem 
at my maximum speed, admittedly about 66% slower than that hi HI!  That 
was with a Globe HG-303 / V-100 and a Drake 2-C.

You can test the timing with a contraption that consists mostly of 
another electrolytic and a neon bulb. The bulb flashed on "make" untill the
second relay made contact, and flashed again on key-up until the first 
relay broke contact.  You could really dial-in the timing of the relays 
with this flasher set-up by adding a small PC-type pot in series with 
either the diode or the cap mentioned above.

Later, I left the VFO on all the time. so I put a small pf NPO trimmer 
cap in parallel with the tuning cap of the VFO and diode switched it in 
and out
of the circuit with the first relay. I adjusted the trimmer so that I 
couldn't hear the VFO in the passband of the receiver during receive, so 
I had break-in
again. Seems to me I put a momentary contact switch in to activate the 
first relay for spotting (of sorts) without putting out a signal.  This 
all was another H&K idea, IIRC.

If you are interested in going this route and can't find the articles 
mentioned, I can probably make a schematic and post it where you can get 
to it.

73,
Tom

Robert & Linda McGraw K4TAX wrote:

>  As to the added TR switching function, I suggest you remove it and
>  use a relay to do the TR switching.

>  73 Bob, K4TAX