[Elecraft] K3 keying an amplifier

[Scott Ellington]

I don't think the diode isolation will work in this case.  

Scott   K9MA


On Feb 16, 2011, at 2:36 PM, Paul Christensen wrote:

>> You might have a problem when only one rig is powered up, with the 
>> unpowered one pulling down the key/control line.   The K3 is OK, as both 
>> outputs are open drain/collector.  If that's also the case with the ICOM, 
>> the "Y" connector should work.  If the ICOM has a pull-up resistor, or 
>> anything except an open drain/collector connected to that control line, 
>> there could be a problem...
> 
> In that case, a Schottky steering diode can be used on the Icom key line.  A 
> 1N914 or 1N400X series may be fine but I've seen instances where the higher 
> diode junction voltage prevents the line from going low enough to circuit 
> ground potential.  Not sure how sensitive the Alpha 9500 is to that effect. 
> I agree with Scott that the K3 should be fine with its open-drain on the 
> MOSFET switch.
> 
> I don't see this issue very often on the amp key line -- I do see it often 
> when trying to use a single CW keyer, feeding multiple transceiver's in 
> parallel, due to the use of pull-up resistors on the paddle key line. 
> Again, Schottky steering diodes used for isolation at the input to each 
> transceiver's CW key line solves the problem.
> 
> Paul, W9AC 
> 
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Scott Ellington
Madison, Wisconsin
USA