Semi-Heath-related ?s...

[Multi-Volti Devices]

I'm thinking separate transistor keying circuits for each line you want
controlled, all driven by the keyer...kind of duplicating the output
transistor of the keyer.

Murray
----- Original Message -----
From: John Clifford <johnclif at ix.netcom.com>
To: <HEATH at LISTSERV.TEMPE.GOV>
Sent: Saturday, October 21, 2000 9:26 AM
Subject: Semi-Heath-related ?s...


> 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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