Joshua Tree Gap Filler Annex

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Used an AN/FPS-18. Operational between September 1960 and June 1961, the site has now been repurposed for civilian uses.

When most AC&W radar veterans think of a 'gap filler,' they usually think of an unmanned radar facility designed to fill the low-altitude gaps between manned long-range radar stations. Gaps in coverage existed due to the curvature of the earth, mountains, hills, valleys, rivers, and so forth. The typical unmanned gap-filler radar annex was comprised of a small L-shaped cinderblock building, with the radar equipment and the data-transmission equipment in one section and one or more diesel generators in the other section. These unmanned gap-filler sites generally had a three-legged radar tower about 85 feet tall. A couple of gap-filler radar towers were four-legged, as they also hosted a forest-fire lookout cabin below the radar-antenna deck. Also, at least one GFA building was not L-shaped, but most were. Unmanned gap-filler facilities in the continental United States (CONUS) used either an AN/FPS-14 or an AN/FPS-18 shortrange search radar having an effective range of 60 to 65 nautical miles. Both models were built by Bendix, and both operated in the S-band at a frequency between 2700 and 2900 MHz.

www.militarymuseum.org/JanesvilleGFA.html