[Milsurplus] Questions about the Collins 18S and 618* equipment

[Michael Tauson]

On Mon, Apr 20, 2009 at 12:09 PM, Mike Morrow <kk5f at earthlink.net> wrote:
> The military version of the 18S-4 is the RT-380/AR, part of AN/ARC-59.

I thought there was a military version but couldn't remember precisely.  Thanks.

> No, the 618M is a VHF-AM aviation-band unit, introduced in the 1960s, IIRC.
> I'd bet some are still flying, just like the contemporary 618T HF set.

It depends on several factors.  A whole bunch of radios got grounded
on 1 January, 1997, when the 25 KCs spacing (720 channel) went into
effect so virtually (if not all) the 180 channel and a good number of
360 channel radios went out of service.  (A number of these grounded
sets are going for outrageous amounts on ePay - maybe for people
building flight simulators?)  I wouldn't doubt that Collins ensured at
least the later versions would remain airworthy, even now with the
1440 channel systems in effect.

>>What (if any) modules are interchangeable between the 618S-1 &
>>RT-311/ARC-38, the 618S-1/MC & RT-594/ARC-38S and between the two
>>groups?
>
> No doubt some modules are common in these four units.

Waste not, want not.  :-)

> There are many
> differences between the contemporary USAF 618S-1 and the USN RT-311/ARC-38,
> but the major one is the use of 144 crystal channels in the 618S-1 versus
> the use of a Stabilized Master Oscillator (SMO, O-215/ARC-38) to generate
> frequency in the RT-311.  The USAF's AM crystal-controlled 618S-1 was
> modified by RCA to the Collins/RCA 618S-1/MC, which provided USB and
> incrementally tuned operating frequency.  The USN's already incrementally
> tuned AM RT-311/ARC-38 was likewise modified by RCA to create the USB
> Collins/RCA RT-594/ARC-38A.  All four of these variants have significant
> differences between them, but also many similarities.

Okay, this gives me some idea how to arrange my thinking on how to
work this out.  I have manuals for the RT-594/ARC-38A and the
618S-1/MC so checking that isn't a problem but it looks like I need to
augment my collection with ones for the AM versions as well to
complete this highly unofficial project ... that kind of grew out of
plans to get one or another version for my own nefarious purposes.
:-)

> The military version of the 618T-2 (400 Hz power) is the RT-695/ARC-94.
> The military version of the 618T-3 (28 vdc power) is the RT-698/ARC-102.
> There are also several other variants, such as the AN/ARC-105.

>From what I can see, the AN/ARC-105 is a pressurized AN/ARC-102.
Since no part of Oahu is very far above sea level, I doubt that
feature is needful.  :-)

> At least as far as the AN/ARC-94 and -102 go, they both used the
> C-3940/ARC-94 control head that allowed full mode selection capability.

That would be the same as the 714E-3 for certain - maybe one of the
others as well.  I don't have the IDs for all the military versions -
or all the civilian ones, for all that - so I'm grateful for notes
like this to help identify what I can.

> The 618T-series has my vote for the best airborne MF/HF set of all time.

I have to agree with this.  (Now, if I could make it tune between 1 KC
spacing ... )

Best regards,

Michael, WH7HG