On Sun, 30 Dec 2007 21:13:03 -0500, Gary Smith wrote:
>By the keyer alone it triggers the 425 but the 425 does not
I ran into this with FT1000MP when keying it through my Herc II.
The problem is that these keying circuits are transistors, some of
the transistors may not get to low enough "on" voltages, and the
rig needs a very low "on" voltage to key it.
In my case, I was keying the Herc II with my computer using
WriteLog, the serial port, and a 2N4123 as an inverter and level
shifter. I also had a diode in series with its collector and
another diode in series with the output of my AEA keyer (so I can
run a paddle plus the computer). Works great with the Titan 425,
but wouldn't key the Herc II.
The fix was a 2-part-er. First, I replaced the Si diodes with Ge
diodes. Second, I reduced the value of the resistor in series with
the base of the 2N4123 so that the computer drove it harder,
reducing the "on" voltage.
The Titan and Herc II are both late 70's vintage designs with all
garden variety discrete transistors, so it's easy to play with
things like this. BTW -- the keying INPUT of the Titan and Herc
are VERY easy to drive -- the key drives something like a 2N5087,
which requires only tens of uA to key it.
Jim Brown K9YC
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