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Re: [TenTec] Corsair II & Titan 425

To: "Gary@doctorgary.net" <Gary@doctorgary.net>,"Tentec@contesting.com" <Tentec@contesting.com>
Subject: Re: [TenTec] Corsair II & Titan 425
From: "Jim Brown K9YC" <k9yc@audiosystemsgroup.com>
Reply-to: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Sun, 30 Dec 2007 20:39:42 -0800
List-post: <mailto:tentec@contesting.com>
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 
>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. 

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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