Return to IFC - Acquisition Radars

AN/FPS-24 or AN/FPS-35
BIG Air Force Radars

for your reference ;-))
- from Wikipedia
- from Radomes
- - note the low frequency (420 to 450 MHz), long wavelength

Subject: R S V Digest Number 5139

Re: Comparing search radars
Fri Aug 17, 2012 12:29 pm (PDT) .
Posted by: "Dave" davidecasteel

One has not seen a "big" search radar until one has seen a AN/FPS-24 or AN/FPS-35. (I'm not counting those multi-array radars that don't have rotating antennae.) It was quite intimidating to climb up onto the AN/FPS-24 antenna reflector and walk out to the tip on the upper catwalk: at that point one was about 140 feet above the ground and 25 feet beyond the extent of the tower (which was itself about 50 feet below)--it was just a little bit scary. I have ridden the antenna standing in that position, but only at "maintenance speed"--1/4 rpm (my Commander dared me to do it, so I did). I was not foolish enough to try it at full speed (5 rmp) because the tips of the antenna were moving at 23 mph then, and a force of 1/2 G was produced--it would have been very dangerous. ("Maintenance speed" also invoked an interlock that prevented radiation, so that was not a worry.)

The AN/FPS-24 antenna was a truly enormous structure. The rotating assembly weighed more than 70 tons and its pedestal on the roof was easily another 20 tons. The "sail" (reflector) was 120 feet across and 50 feet high, painted with a red and white checkerboard pattern. The feed horn was about 5 feet wide and 8 feet tall and was at the end of a short section of waveguide that was big enough to sit up in (not recommended when the radar was radiating!). The feed horn and waveguide were supported by a huge tubular steel boom. All this was due to the frequency of the radar being so very low (actually in the VHF band, 214-236 MHz).

Some of the internal components of the AN/FPS-24 were also quite imposing. The RF energy was carried to the feedhorn via large 9" diameter rigid coaxial cables, which was in sections connected together with crimped clamps that made them look like steam pipes. The condensers (capacitors) that were part of the antenna tuning system looked like large round tanks. And there was piping for cooling oil and water running all over the place. It looked more like a factory than a radar set.

I have no experience with the AN/FPS-35 except to note that its antenna was almost as big as that of the AN/FPS-24. Because it operated at almost double the frequency of the -24, I presume its internal components were not as big, by comparison. I can tell that its feed horn support was not as beefy from looking at photos.

I consider it a travesty that at least one of those huge radar systems had not been preserved as a monument somewhere. They truly represented the zenith of radar development at that time and were very impressive structures. The only element still in place anywhere is the AN/FPS-35 antenna at Montauk Point in New York (the electronics is gone). I believe it to be imperative that this remaining relic be preserved.

David E. Casteel
Captain, USAF (ret)
former Radar Maintenance Officer, 689th Radar Sq, Mt. Hebo AFS, OR
"David in Dallas, Texas"