[Elecraft] K3 external qro keying line

[Don Wilhelm]

Guy,

I do not understand your confusion.  The statement is that KEYOUT can 
key up to +200VDC @ 5A.  It does not matter whether there is a relay in 
the K3 or not (it actually is a HEXFET), that statement specifies the 
limits that the circuit in the K3 can handle. 

The path will be a closed circuit on keying the K3 and will be open 
circuit during receive.

The voltage and current as well as the polarity are determined by the 
device (usually an amplifier) to be keyed.  One can measure the 
requirements with a DMM - measure the voltage at the amp's PTT input - 
if it is positive and less than 200 volts, all is OK so far, but there 
is one other step - put the DMM in current measurement mode and connect 
the DMM to the amp PTT input again - if the current is less than 5 amps, 
the K3 KEYOUT can handle it.  The conditions must be less than the 
KEYOUT maximum for voltage and current, and the voltage polarity must be 
positive.  Those are the maximum ratings that the K3 switch can handle.

73,
Don W3FPR


Guy Olinger, K2AV wrote:
> The sentence does not fix whether the relay is in the amplifier or in the 
> K3.  Perhaps:
>
> "...is transistor output for keying amplifier T-R circuits, ONLY positive 
> voltages up to +200VDC @ 5A."
>
> Could a future mod include a blocking diode for negative keying voltages if 
> the circuit will not sink high negative voltages without damage.
>
> 73, Guy.
>   
>