[Collins] 18S-4 & ARC-38A

[Dr. Gerald N. Johnson]

On Mon, 2006-04-10 at 09:12 -0700, Michael Tauson wrote:
> Hi, Folks,
> 
> I am about to take delivery on a Collins 18S-4 and a C-3428/ARC-38A.  Yes, I
> know they don’t go together but the timing is such they’re both coming about
> the same time but from two different sources.
> 
> What I would like is the connectors to match the 18S-4, the RT-594/ARC-38A and
> the C-3428 control head.  (Mounts for the two RT sets would be nicer but I’ve
> learned not to look for miracles. <G>)  Also, while I’ll want a manual later
> on, for the moment I would like to find a schematic for the 18S-4 and its
> control box.  Failing connectors, the pinouts would be nice but they’ll be in
> the manuals/schematics so this is not an issue.  Fair has the manual for the
> ARC-38A and the frequency setting book (as well as the RT-594) so they aren’t a
> real problem.  
> 
> While on the subject, as I understand it, the RT-594 is USB only as opposed to
> USB/LSB.  Has anyone tried modifying it for LSB or for making the channel
> selection a bit “rubbery” to allow tuning between the .5 or 1 Kc selections? 
> (This last is more for curiosity than anything.)

There might be a couple ways to get LSB. Surely its more than single
conversion, moving either oscillator to the other side can change the
side band without wrecking the calibration, probably. Or like the S-
line, moving the BFO to the other side of the filter and adjusting the
VFO to match could work but probably makes for inconvenient display on
LSB. Then many Collins mechanical filters were made in USB/LSB pairs for
the same carrier frequency so all it would take to get LSB would be to
switch in the other half of the pair. Those pairs tended to be
asymmetrical with a sharper cutoff at the carrier side than the high
audio side of the pass band.

Rubbering is most likely easiest by rubbering the reference oscillator
for the synthesizer, unless there is an offset oscillator and then
rubbering the offset oscillator also works. Often in vintage
synthesizers there is an offset crystal because the programmable TTL
counters couldn't count to 30 MHz reliably.

I'd guess that the connectors are standard Mil Spec, probably catalog
items, but they could have been permuted for insert position compared to
shell indices. The makers allowed for that, but distributors often
don't. Could be threaded series or bayonet series and still be in the
Mouser, Allied, or Newark catalogs.
> 
> These sets will eventually find themselves aboard the Jeep for use in
> CW/RTTY/*shudder* voice mode operation though I’m not entirely sure I know how
> I’ll handle running the 18S-4 RTTY yet.  
> 
> Okay, you may now start the loud derisive laughter.  I’m used to it.  *sigh*
> 
> Best regards,
> 
> Michael, K3MXO
> 

-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer