[TenTec] Corsair II & Titan 425

Dr. Gerald N. Johnson geraldj at storm.weather.net
Tue Jan 1 11:43:44 EST 2008


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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