TD-285 Gap Filler Multiplexer Set - A Gap Filler Radar Multiplexer set built by Budd Electronics.
TD-285 Gap Filler Multiplexer
From MIL-HDBK-162A 15 Dec 1965:
The Multiplexer is a link in the transmission of data from both long-range radar and gap-filler radar sites to the SAGE System Central Computer. The Multiplexer receives any combination of inputs, up to six, from the FST-1 or FPS-14, and FPS-18 Gap Filler radars.
The gap filler outputs are interleaved with the output of a long-range radar site. The information is then transmitted over a single pair of telephone wires. Signals from the AN/FST-2 control the reading out and transmission of the store information.
Permission to transmit is alternated between the stored gap filler data and long-range radar output. This permits the use of only one pair of telephone lines instead of seven. Multiplexer operation can be remotely controlled from a distance up to 150 feet.
Winkler, David F., Searching the Skies: the Legacy of the United States Cold War Defense Radar Program, USAF Hq Air Combat Command, 1997, 192 pages, Pdf