On Thu, 2006-10-12 at 13:02 -0700, Chortek, Robert L wrote:
> Fellow Reflectees,
>
> Can anyone explain how to hook up a PTT Output for an accessory device
> WHILE AT THE SAME TIME, using the two Amp relay outputs? I need to key
> an amp AND an accessory device at the same time (turn off the accessory
> while in xmit), so as not to fry the accessory. The I/O jack on the
> back won't do it, because that is an INPUT. The only thing I can think
> of is to use a splitter on one of the amp key outputs, and run one side
> to the amp and the other to the accessory.
>
> Can this be done, and if so, can anyone help me?
>
> Thanks,
>
> Bob/AA6VB
>
The quickest is to key a multiple pole relay with the exciter output,
and wire each of the relay poles to a separate device. The annoyance is
the relay will not be perfectly quiet. You would probably need a power
source for the relay (and a diode across its coil to absorb inductive
kick at turn off), presuming the exciter key output is a ground. Other
than the click of the relay this will work every time in every
situation.
If the exciter provides a ground, and each controlled device needs a
ground I'd go with a three transistor circuit. First a PNP transistor
with emitter to + 12, base to the exciter output through a 1.5K
resistor, and collector through a pair of 1K resistors to the bases of a
pair of NPN transistors. Those NPN transistors would have their emitters
grounded and each collector would key a controlled device. I'd also put
a 1K resistor from base to emitter on each transistor to be sure that
any internal leakage was shunted so the transistors turned off well. The
NPN transistors need to be able to carry the control current and stand
the controlled device's open circuit voltage. Otherwise they are not
critical.
--
73, Jerry, K0CQ,
All content copyright Dr. Gerald N. Johnson, electrical engineer
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