[Elecraft] External keyer question...

[Don Wilhelm]

Steve,

You can damage the K2 by applying a current source (or too high a voltage)
on the keying line.  To properly key the K2, drive the keying line with a
set of contacts (like a relay contact) or with an open collector switching
NPN transistor - the key line connects to the collector and the emitter goes
to ground.  A PNP could also be used, but I find that using 'upside-down'
transistor switches can make my brain hurt.

A transistor such as the common 2N2222 will do the job.  Drive the base with
the keyer's +20 volt output through a series resistor (10K will do) and
place a 2K resistor from the 2N2222 base to the emitter.  The emitter goes
to ground as does the common from your keyer.  On the output side - connect
the collector to the K2's keying line and the emitter to the K2 ground
(chassis).  It should key the K2 just fine.

In case the 2N2222 keying transistor does not switch for you, double check
the key-down output voltage from your keyer.  The resistor values I stated
should provide good switching if your keyer does indeed have +20 volts out
key-down.  If the resistor load drops significantly below that voltage, you
may have to reduce the 10K series resistor - you should have 3 to 4 volts on
the 2N2222 base key-down and 0 volts key-up.

Lastly, just set the K2 to INP HAND and connect the 2n2222 collector to the
dot paddle input on your K2 - or if you prefer to use a paddle directly
connected to the K2 at the same time as you have your keyer connected, use
2-2N2222's in your keyer interface - connect the bases and emitters
together, and drive the K2 dot line with one collector and the dash line
with the other collector.  That may be just as easy as using the two diodes
in conjunction with the transistor switch.

73,
Don Wilhelm  - Wake Forest, NC   W3FPR home page: http://www.qsl.net/w3fpr/
  QRP-L # 485   K2  SN 0020   mailto: w3fpr@arrl.net

----- Original Message -----
>
> My question is which keying line to use to key the K2 directly from one of
> the SA-5010's keying outputs. There are two of them, one - and one + .
Each
> of them terminates in an RCA phono-type plug on the keyer's rear apron.
> I'll be glad to remeasure the keyed output voltage from the SA-5010 if
it's
> needed.  (My recollection from bench-testing the keyer a couple of weeks
ago
> was that both lines provide about +20 or -20 VDC when the keyer is keyed,
> but I don't recall for sure
>
> I can build up the "auto detect" device requiring two diodes as
illustrated
> on the K2 Manual (p. 92) with no problem. But my concern is which of the
> SA-5010 keying lines to use to connect to the K2. The two diodes shown in
> the K2 illustration may not like one or the other of them.
>
> Anyone have any suggestions?
>
> Thanks for any comments.
>
> 73
>
> Steve Banks
> K0PQ
> K2 S/N 1599
>
>
>
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