[CQ-Contest] CW Keying Cable

[David Gilbert]

Some optocouplers have single transistor outputs, and some have 
Darlingtons (less common).  The Darlingtons have higher gain (more 
sensitive to input current) but like any Darlington they won't pull down 
to less than about one volt or so.  An optocoupler with a single 
transistor output is the best way to go as long as it is driven hard 
enough at the input (usually about 10 milliamp or so) to fully saturate, 
but one way to make a Darlington version work is (as Pete suggests) to 
follow it with a simple PNP pulldown transistor.

73,
Dave   AB7E



Pete Smith wrote:
> At 09:02 PM 11/9/2008, Dennis Vernacchia wrote:
>   
>> Mal,
>>
>> Also W1GEE makes em
>>
>> http://www.hosenose.com/interfaces.asp
>>
>> Be sure the one U buy uses an Opt Coupler typr device and not descrete
>> transistor(s) - The Optos are far more reliable !!!
>> I know W1GEE uses the Opto circuits
>>     
>
> Except that, with some radios, some optocouplers do not pull the key or PTT 
> lines down close enough to zero.  I'm sure there are tricks to this - the 
> selection of the optocoupler or some sort of "pull-down" - but with garden 
> variety ones, neither my TS-930 or Mark 5 worked properly.  The 930 
> wouldn't PTT, and the Mk5 wouldn't key CW.
>
>   73, Pete 
>
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