The 42 foot cassegrain horn

The 42 foot Cassegrain horn antenna

(also known as the TT&C antenna)

The first OTC (Australia) Earth Station antenna was a fully steerable 42 foot aperture cassegrain-fed folded-horn antenna, with interacting parabolic and hyperbolic reflectors.

The design of the dish was pioneered by the Aero Geo Astro Corporation. It had a number of advantages over the larger horn antennae. Details here.

The structure was built by the Rohr Corporation of California for Page Communications. (Rohr were well known in building similar structures – they won the contract to build the 64m Mars dish at Goldstone. The project was overseen, and the electronics installed by Page Communications Corp.

Five of the CassHorn antennae were built:

Four were built under contract to COMSAT Corporation, for installation at Andover, Maine; Brewster Flats, Washington; Carnarvon, Australia; and Paumalu, Hawaii. However, Australian authorities required that the Carnarvon station be owned and operated by OTC (Australia).

A fifth 42-foot station was built and assembled as a spare at Page Communications’ Taylors Island test site in Maryland. When RCA won the bid to supply an Earth Station for Thai PTT (even though RCA did not have an Earth Station they could sell!), the fifth station was sold to RCA and was installed at Sattahip, Thailand.

(Above information courtesy William Lightfoot, Program Manager for the 42-foot stations.)

The OTC Carnarvon 42-foot Casshorn is the last remaining example of this design of antenna anywhere in the world.

Page Communications’ Tom Minton recalls (2023),

[The 42-foot stations] we deployed, Carnarvon being one, were manufactured in several places:

The reflectors and by the now out of business Dominion Bridge Company in Canada.

The feed systems in the US (Virginia).

The low noise amplifiers, in many places, one being Milan, Italy and another Montreal Quebec, Canada.

The electronic tracking system in a Los Angeles CA suburb. Forget which one.

[At Carnarvon] our teams assembled all of this on site, and I led a team that did the final measurements of system performance using as I recall, the stellar constellation Cassiopeia A and a transmitter we installed on a tower across the Gascoyne River north of Carnarvon. I believe it was on the property of a school or orphanage.

The first – though unscheduled – assignment for the Carnarvon antenna was to test links to the UK through Intelsat-2A on 29 October 1966. Three weeks later, when the satellite was again in a favourable position, it was used for the Down Under Comes Up Live broadcast.

The antenna began communicating through the Pacific-1 (Intelsat-2B) on 11th January 1967 – three weeks after that satellite’s launch.

Three weeks later, in February 1967, it commenced its role as satellite relay station in support of the NASA MSFN Carnarvon Tracking Station.