[ARC5] Chirp in Command Set transmitters.

[Morrow, Michael A.]

David Stinson wrote: 

>Chirp in the ATA/274N/ARC-5 transmitters can have several causes:
>
>1.  If keying with the selector relay (the one on the side wall
>    and the best way to do it), be sure the oscillator set of 
>    contacts makes before the PA set of contacts.

I've not powered up an AN/ARC-5 transmitter since the 1960s (as a novice
rig), and of course that was in the era when gross modifications were a
matter of course.

In the original system design, as you mention, all relays inside each
transmitter are transmitter select relays (not PTT or CW keying relays) that
are energized continuously when that transmitter in the rack is selected for
use from the remote control box.  For CW keying, the dynamotor (which in
phone mode doesn't run when in receive mode) runs continuously and a relay
in the modulator/dynamotor unit keys the HV to the whole transmitter,
including the oscillator, on key-down.  What I've always wondered is, in a
completely unmodified system using the dynamotor/modulator, what the
resulting CW signal must sound like.  One supposes there must be a fair
amount of chirp.  For an *authentic* vintage signal that re-creates the
characteristics of the original installation, this would be *the* way to
operate the transmitter.  I have a complete, all-original (except for an
FT-225 and -228) NOS two-transmitter, three-receiver SCR-274-N set, but I'm
not about to power that up.

If I recall correctly, the military manuals for these sets state that 12 wpm
was about the maximum recommended keying speed.

Mike / KK5F