[Milsurplus] Command Set Transmitter Keying

[Mike Morrow]

>David Stinson ... has written several times about running the
>transmitters as is without any extra regulation and without chirp,
>click or other unpleasantness.

The remark that follows is not germaine to the set in the
earlier thread (a command set transmitter with significant
modifications).

Often those wanting operate an ATA, SCR-274-N, or AN/ARC-5 transmitter
in stock original condition will try to key the transmitter by
keying the K53 and K54 relays in the transmitter.  But that is not
how the system was designed.  K53 (Oscillator HV and PA cathode) and
K54 (antenna connection) relays are NOT keying relays.  They are
transmitter *select* relays.  They are energized ONLY, but CONTINUOUSLY,
when that particular transmitter in its rack has been selected at the
control box.

The only relay that operates on key-down in the original system design
is K52 in the modulator unit.  This relay supplies ALL B+ (Oscillator,
PA screen, and PA plate HV) to all transmitters in the rack.  But the
only transmitter that will function will be the one that has its K53
and K54 select relays energized.

So, for the ATA, SCR-274-N, and AN/ARC-5 transmitters, if you want to
duplicate the methods used in the original system, you must energize
K53 and K54 continuously, and key the three HV sources going to the
transmitter.  Using K53 and K54 to key the transmitter is mis-using
select relays as keying relays, and thus it is not operating the
transmitter as it was designed to be. 

I'm not suggesting that will eliminate CW chirp, only that this is
the way the system was designed to function.  As Dave Stinson has
pointed out, attempting to key a transmitter by keying K53 can cause
problems if the sequence of contact closures on the K53 relay doesn't
cause oscillator HV to be applied before the PA cathodes are grounded
by the same relay.  This isn't a problem in the original system,
since K53 would be continuously energized in the selected transmitter.

Mike / KK5F