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

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 <[email protected]> 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: [email protected] <[email protected]> On Behalf Of Michael St. Angelo via MRCA
Sent: Sunday, January 18, 2026 10:53 AM
To: [email protected]; [email protected]; [email protected]
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

-=-=-=-=-=-=-=-=-=-=-=-
Groups.io Links: You receive all messages sent to this group.
View/Reply Online (#4911): https://groups.io/g/MMRCG/message/4911
Mute This Topic: https://groups.io/mt/117332342/1233693
Group Owner: [email protected]
Unsubscribe: https://groups.io/g/MMRCG/unsub [[email protected]]

-=-=-=-=-=-=-=-=-=-=-=-