Has anyone tried a darlington pair (beta multiplier)
in place of the keying transistor? This should draw
very little current from the interface.
Mike, W4EF
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From: Pete Smith[SMTP:n4zr@contesting.com]
Sent: Monday, January 25, 1999 12:41 PM
To: trlog@contesting.com
Subject: Re: [TRLog] Need help with Keying/PTT/Paddle interface
At 08:15 PM 1/24/99 -0800, n6tr@teleport.com wrote:
>
>This sounds like the on voltage of the transistors are too high.
>This can happen due to low beta in the transitors. You can probably
>fix the problem by putting the emitter of the CW transistor directly
>to ground. However, now your transmitter will key when you reset
>the computer until you start up the program.
>
>This is why I went with relays for everything in my latest swtich
>box. I used a radio shack reed relay for CW and any old relay for
>the PTT. That way you are providing dry contacts to the radio and
>you don't care about polarity or voltage drop any more.
Boy you got that right! My opto box would key the rig from my LPT2 but the
"on" voltage was too high to trigger the VOX. I changed port cards and
then the interface wouldn't do anything but key the sidetone on the rig.
Reduced the series input resistor value, but still not getting low enough
to key the rig. Had to move the interface to another parallel port that
(apparently) has better voltage characteristics on the lines used. Too
much like work. I'm going reed relay in the next iteration.
73, Pete Smith N4ZR
n4zr@contesting.com
Loud is.
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