The Site was utilized by the USAF as an Aircraft Control & Warning (AC&W) site from 1958 to 1970. This AC&W Site was part of the Semi-Automatic Ground Environment (SAGE) radar system. The Former Janesville GFA utilized an AN/FPS-18 model gap filler radar, where "AN/FPS" is an acronym for Army-Navy Fixed, Pulsed radar, Search electronic device (Radomes, Inc., 2004). Figure 3-1 shows an aerial view of the Site. Radomes, Inc., a non-profit veterans society dedicated to radar military history and technology, summarizes the function of these facilities:
"During the late 1950s another area of progress was the development and deployment of AN/FPS-14 and AN/FPS-18 gap-filler radars. Having a range of around sixty-five miles, these radars were placed in areas where it was thought enemy aircraft could fly low to avoid detection by the longer-range radars of the permanent and mobile radar networks. Gap-filler radar deployment peaked in December 1960 at 131 sites throughout the continental United States." (Radomes, Inc., 2004).
The Site consisted of two parcels totaling 37.42 acres: 37.12 acres of USFS unimproved road 2 miles more or less (Thompson Peak Tower Access Road, "unimproved jeep trail); and a 0.3 acre building site (130 feet x 100 feet) (Figure 3-2, NARA document). The AN/FPS facility is further described:
"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" (Radomes, 2004).
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