CW keying interfaces

Peter G. Smith
Wed, 25 May 1994 12:12:19 -0700 (PDT)

I just received an advert from a company offering a keying interface
compatible with CT.  They assert that if you are using an LPT port that
the basic transistor/resistor interface is risky because the LPT port is
directly on the computer bus and therefore particularly susceptible to
voltages from either the transmitter or from RF.  Their solution is to use
an optoisolator in the interface.  Is this necessary? 

Another question -- I'm currently using the N3JT interface but am about to
change because it has a strange quirk when using it with N6TR's logging
software, which I use as well as CT and my own morse keyboard software,
all with the same interface (at different times).  When I interrupt
transmission of a CW character using the <escape> key, if N6TRlog is in
the middle of a key-down element of a character the key stays closed!  I
literally have to interrupt power to the interface to get it to unkey my
rig.  By the way, when I reconnect the power it doesn't go key-down again. 

Clearly this won't do.  Tree says he knows of no explanation in the
software, so I'm wondering if anyone else using N6TR software also has the
N3JT interface and has or has not experienced this glitch.  I should
mention that my N3JT interface is an early prototype, not the production
version.  And no, it's not RF, because this happens even when I'm only
keying the sidetone. 

73, Pete
NOTE: New Address