On 9/30/2011 2:04 PM, Owen Duffy wrote:
Jeffrey wrote in news:j64hp4$i7g$1@dont-
email.me:

The two signals are essentially a "request to tune" and an "tune
complete".

That is not quite correct.

Did you miss the word essentially?

Since it bothers you. From LDG "Start Line." Ground this from an
external switch or open collector to initiate a tuning sequence by
the external tuner.

And "Key Line" This is similar to a PTT line to the transmitter,
but in this case tells the transmitter (which is capable of doing
it) to, regardless of mode, transmit a low lever CW carrier.

When the key line changes state because of a request to tune, it
turns on the transmitter. When tuning is complete, the key line
toggles back to it's normal state.

Though the protocol is not published by Icom, and the implementation varies
a little from radio to radio, the four wires are usually labelled and none
are "tune complete".

If you put an indicator such as an LED on the key line watching it
change state is a pretty good indication of "I'm tuning" and "Tune
complete" regardless of what it's called.

Jeff

--
"Everything from Crackers to Coffins"