Thanks to W1WEF, N2IC, N2NT, VR2AX, AA4NU, WW4LL, K5TR,
W6OPO, K6XX, KL7RA, and K0EJ who responded to my question.
The consensus is that there are two things which are contributing
to the symptom that I am experiencing. First, the AL-1200 relay
is notoriously slow, especially on the really old models like I
have here (S/N 380.) Second, the SWR protection circuit in the
IC-781 appears to be quicker and/or more sensitive than the IC-765,
which explains why the symptom occurs with one model of radio, but
not with the other.
I can indeed see the SWR meter on the IC-781 jump a few extra tics
as the AL-1200 relay closes in semi break-in. When I use a 10ms PTT
key-ahead, or manually close MOX, I don't see the SWR jump on the
first CW character, and power rises instantly as it should. It seems
that the slow relay response of the AL-1200 is causing the IC-781 SWR
shutdown circuit to kick in momentarily, resulting in the slow-rising
output power.
The problem has never been an issue with CW or SSB contesting,
because I always have used a 10ms key-ahead PTT closure before
the first CW character or SSB syllable. However, the slow relay
is a problem with semi break-in CW, and is always a problem in
true FSK RTTY. A PTT closure sends a tone instantly, so it is
not possible to close the PTT ahead of time with FSK RTTY.
I have a couple of things to try. One is an amp relay speed-up circuit
like K6XX's. The first attempt I built had no effect, but I must have
had a bad component (or something else wrong -- I don't know.) I've
also ot a AL-1200 QSK board from a flea-market purchase years ago that
I need to locate and install. I haven't bothered with QSK so far, as
I usually operate CW contests SO2R. (For you non-contesters, SO2R is
listening on one radio while simultaneously transmitting on another.)
Thanks again for the many responses from folks who know what they
are talking about. I appreciate the education and the the advice.
73
-Kirk K4RO
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