[TRLog] Universal CW Keying Circuit

[k6ll@juno.com]

On Sun, 4 Jul 1999 16:06:41 -0400 "Jack Trampler" <n2jt@fast.net> writes:
>
>Recently my FT-1000MP took ill and I had to return it to Yaesu.  I 
>inquired
>on this reflector about keying the Drake T4XC with the keying circuit 
>that
>appears in the TR manual.  I received many replies (thank you to all) 
>and
>there were two routes to choose from.
>
>Since the Drake uses grid block keying, the first option was to change 
>the
>transistor to a PNP type capable of handling the keying voltage.  
>This
>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.  
>Pete,
>N4ZR said:
>
>>I believe the C-line uses -60 to -70 volts DC for grid block keying.  
>As
>>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 
>5
>>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 
>all
>rigs.  I used a Radio Shack 5VDC reed relay (part #275-232) with the 
>coil
>connected between the transistor collector and the junction of pin 17 
>and
>the 1K ohm resistor that goes the  emitter.  Pin 17 supplies 5 VDC.  
>I
>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 
>additional
>current damage the computer or serial port?  I would think not, but I 
>don't
>have any specs on this.  If anyone know for sure, I would appreciate 
>hearing
>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
K6LL@juno.com

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