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[TRLog] Universal CW Keying Circuit

Subject: [TRLog] Universal CW Keying Circuit
From: (
Date: Sun, 4 Jul 1999 20:17:50 -0600

On Sun, 4 Jul 1999 16:06:41 -0400 "Jack Trampler" <> writes:
>Recently my FT-1000MP took ill and I had to return it to Yaesu.  I 
>on this reflector about keying the Drake T4XC with the keying circuit 
>appears in the TR manual.  I received many replies (thank you to all) 
>there were two routes to choose from.
>Since the Drake uses grid block keying, the first option was to change 
>transistor to a PNP type capable of handling the keying voltage.  
>measured -34.5 volts at the key.  The problem with this option is when 
>my MP
>comes back I will have to change the transistor again.
>The second option was to use the existing circuit to key a relay.  
>N4ZR said:
>>I believe the C-line uses -60 to -70 volts DC for grid block keying.  
>>such the polarity is wrong, and the voltage rating would be exceeded. 
> The
>>simplest fix probably is to put a dip relay in the collector, provide 
>>volts to operate it, and use the relay contacts to key the C-line.
>I decided to go the route of the relay as it will be compatible with 
>rigs.  I used a Radio Shack 5VDC reed relay (part #275-232) with the 
>connected between the transistor collector and the junction of pin 17 
>the 1K ohm resistor that goes the  emitter.  Pin 17 supplies 5 VDC.  
>tested this relay up to 50 WPM and it works very well.
>The only question I have now is the relay draws 20ma.  Will this 
>current damage the computer or serial port?  I would think not, but I 
>have any specs on this.  If anyone know for sure, I would appreciate 
>from you.

Sometimes it's difficult to get an authoritative answer on a
question like this. Anyway, here's one method that Tree
recommended to me last week that will work for sure.

Connect an external voltage source to your relay, +12vdc
or +5vdc, or whatever is required. Connect the other side of
the relay coil to the collector of the transistor in the regular
positive keying circuit.

Dave Hachadorian, K6LL
Yuma, AZ

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