Semi-Heath-related ?s...

[John Clifford]

Greetings,

I'm trying to use my MFJ memory keyer to both key my HW-9, and mute my Drake
R8A.

First, I tried to hook all three up in parallel.  Found out this didn't work
and muted the HW-9 but not the R8A (thought about it a little bit and
realized why... we'll leave that as an exercise to the reader).  Next, built
a cable w/three male RCA plugs on it, wired in series (each connector was
'daisy-chained' to the next one).  Didn't work.  Figured out it was because
the R8A puts out ~6v, while the HW-9 puts out ~14 volts (matches incoming
power voltage). My cable ran the + probe from the HW-9 to the + probe on the
R8A.  I figured that, because the HW-9 was overloading the 6v on the Drake,
that explained why there was no voltage drop to ground that would have
engaged the muting circuitry on the latter.  Of course, since there was
still ~6v coming back to the HW-8, it didn't transmit either.  Remembering
my blown LM388, I decided to unplug everything and ask a few questions that
truly demonstrate my woeful ignorance of all things electronic.

I'm basically using a SPST switch (the keyer) to control two circuits.  Both
circuits need to be grounded in order to engage them (muting on R8A,
transmit on HW-9).  I know that I could wire a relay into the keyer/HW-9
circuit and control the R8A, but I don't want the clackety-clack of a relay.
I'd like to figure out a way to modify my cable with perhaps a diode (to
control current flow) and a resistor (to drop the voltage to the R8A), but I
can't think of a way to make this work.  My limited knowledge is telling me
that this is a classic application for a simple circuit using a transistor.
Is this right?

Secondly, I know that more than one transistor will be needed.  I have yet
to see any circuit that actually works which doesn't include the obligatory
resistors and capacitors.  My problem is, while I know what these gizmos do
from an elementary and theoretical point of view, I cannot possibly see how
they add any value to the circuit.  But, I'm sure that others don't throw
these components in merely because they're cluttering up the bottom of the
spares box.  Any help here would be appreciated.

In closing, the reason I decided to get my license and fool around with
radios was not merely the magic of communicating through the ether, although
that is pretty amazing when you think about it.  The amazing thing about
radios (to me) is that someone can arbitrarily (?) arrange a collection of
parts and get sound to magically appear.  Because I cannot (yet, but I
remain hopeful) comprehend how this works, I am fascinated by it.

 - jgc

John Clifford
Weapons Safety, Inc.
13215 SE 30th St.
Bellevue WA  98005

  vox: 425-649-8623
  fax: 425-644-5302
email: johnclif at weaponssafety.com
 http: www.weaponssafety.com

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