On Sun, 2007-12-30 at 20:39 -0800, Jim Brown K9YC wrote:
> 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
> trigger
> >the Corsair.
>
> 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.
If the output devices in the keying sources are open collector, the
diodes are not needed. You can "wire-OR" as many as you like. Which
works like NAND logic because key closures are inverted logic with low =
TRUE.
And if the output devices were power MOSFETs the voltage drop could be
even lower than the saturated bipolar transistor.
>
> 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.
>
> 73,
>
> Jim Brown K9YC
>
73, Jerry, K0CQ
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