[Milsurplus] [MMRCG] [MRCA] Univac Aircraft Antenna Coupler

[boeing377 at gmail.com]

ERA coupler was used with ARC 65. I do not recall it having a separate
control box. ERA was housed in a pressurized case to prevent arcing at high
altitudes when carried in an unpressurized area of the host aircraft.

Spoke with a restored USAF radio tech who maintained ARC 65 systems. He
said the ERA was a fantastic HF coupler. Far more reliable than the RT 400
ARC 65 transceiver.

Mark
AF6IM

On Sun, Jan 18, 2026 at 11:22 AM Jim Whartenby via Milsurplus <
milsurplus at mailman.qth.net> wrote:

> Far from an expert, but thanks Scott!
> The first generation ERA 3000 (later named Univac then Unisys) coupler was
> vacuum tube powered, the second generation ERA 3250 was all solid state.
> Both are stand alone in that the coupler tuning is controlled internally
> using the frequency discriminator.  It should work with any transmitter or
> transceiver.  The first generation coupler has the control electronics
> mounted in the same box, the second generation is made up of two boxes, the
> coupler and the control unit.
>
> It is an interesting story of how a computer company became an automatic
> antenna tuner supplier.  Evidently, USAF wanted a second source for the RCA
> designed coupler for the ARC-21 transceiver which is also all vacuum tube
> powered with the exception of a Selenium rectifier.
>
> The VIP page does not have a decent photo of the first generation
> coupler.  I sent them a few photos but the page was never updated.  I guess
> that those responsible for the coupler page are no longer with us.  It
> would be a shame to harvest the coupler for it's components but a little
> bit of history slips through our fingers every day.
>
> Below is the first generation, ERA 3000, coupler still mounted on the
> shipping plywood
> [image: Inline image]
>
> Jim
>
> Logic: Method used to arrive at the wrong conclusion, with confidence.
> Murphy
>
>
> On Sunday, January 18, 2026 at 12:11:08 PM CST, Scott Johnson via
> groups.io <scottjohnson1=cox.net at groups.io> wrote:
>
>
> Jim Whartenby is the resident expert on these couplers, but it is P/O the
> ARC-65 SSB transceiver used on the B-52 and KC-135 until they were fitted
> with the ARC-190.  That transition happened in the 1980s, so it is likely
> that coupler never saw service after it was serviced. Both Jim and I have
> ARC-65s and ARC-21s (the AM version which was modified for SSB to become
> the ARC-65 in the late fifties).
>
> Regards,
> Scott W7SVJ
>
> -----Original Message-----
> From: mrca-bounces at mailman.qth.net <mrca-bounces at mailman.qth.net> On
> Behalf Of Michael St. Angelo via MRCA
> Sent: Sunday, January 18, 2026 10:53 AM
> To: mrca at mailman.qth.net; milsurplus at mailman.qth.net; MMRCG at groups.io
> Subject: [MRCA] Univac Aircraft Antenna Coupler
>
> Going through some military stuff on a snowy Sunday and found a couple of
> aircraft antenna couplers I got surplus years ago. They were designed by
> ERA and this model was built by Univac. The are an HF Coupler mounted in
> the vertical stabilizer of a plane such as a KC-135 to tune the probe HF
> antenna. They were hermetically sealed and basically consist of a rotary
> inductor and vacuum variable capacitor tuned via a discriminator circuit.
>
> I've attached a couple of pictures. The discriminator section has the
> cover removed. They were last services at Warner Robbins in 1965. I was
> told they require 28 VDC and 100 AC 400 Hz. The RF connection is made via a
> C connector (my favorite RF connector)
>
> I was going to use the components in a tuner but want to get in
> operational in their original state. Does anyone have any documentation
> about the tuner or it's controller box?
>
> Thanks in Advance,
>
> Mike N2MS
>
>
>
>
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