I was the first assigned Radar Maintenance Officer for the AN/FPS-24 radar set installed at Mt. Hebo AFS, Oregon. I was originally assigned to the unit in February, 1960, and was an "overage" at the time-Lt. Barry D. Kushner was already on site and functioning as the RMO for the existing equipment. When work began on the new Frequency-Diversity (FD) radar installation, I was sent to train on the prototype AN/FPS-24 unit at Eufaula AFS, Alabama later that year. Upon return to Mt. Hebo, I was given the responsibility for the new radar equipment and its maintenance, and was the first AJO (Anti-Jam Operator), too.

Although the location had much to recommend it as a site for an FD radar (large view of the ocean to westward and the ability to "see" fighters coming off the runways at Portland Air Base), the mountain itself was not hospitable and provided many interesting challenges:

1. Weather. Long known for its extreme weather conditions, Mt. Hebo had some of the most severe Winter conditions experienced anywhere in the "lower 48" states, with lots of snow and ice loading and very high wind speeds-normal winds during the Winter months typically ran 50 knots gusting to 100 or more and some peak gusts at more than 150 knots. Mt. Hebo is considered one of the "wettest" places in the US with more than 300 inches of rain and snow annually; temperatures during the Winter months are cold enough to convert the rain to ice. Snow frequently piled up high enough to cover the metal buildings used for most functions. The high winds made it necessary to tie those building down with cables so that they would not blow away. I remember when the AN/FPS-24 tower was first completed (minus the antenna), the contractor had the rooftop completely cleaned off and locked the only access hatch with cables and padlocks to prevent any incidents until the antenna installation was to commence. One weekend shortly afterward, the mountain had endured a high-wind condition and the contractor went up to survey his tower when the winds had died down. He discovered that the roof was littered with small stones ranging in size from gravel to pieces about an inch across. He accused his men and the troops of throwing stones to the top of the tower to get his goat. However, when he tried to throw stones up there from the ground (the tower was 85 feet high) or from the catwalks of the nearest radar towers he was unable to do so. I and others wary of the local conditions have always believed that those rocks were BLOWN up there by the high winds. I have personally observed icicles 3 feet long hanging from the railings on that tower, but at an angle of 70 degrees from the vertical!
2. Geology. When the soil surveys were made of the mountain, it was discovered that the area where the AN/FPS-24 was to be placed was laced with nearly vertical crazes and faults and could not support the normal weight of the intended building (even absent a radome). Thousands of cubic yards of liquid concrete grouting were pumped into the mountaintop to bind it together and make a firm foundation for the structure, and the radar building itself was made lighter than standard by the use of corrugated metal walls instead of the poured concrete used at other locations.
3. Electromagnetic Radiation. Mt. Hebo was also home to a number of other agencies` electronic equipment, most particularly a TV "repeater" site for the town of Tillamook, Oregon, about 12 miles "as the crow flies" north of the station. This was VHF television, and one of the channels in use was Channel 13, the top frequency of this band. As it happened, the frequency range of the AN/FPS-24 radar was 214-236 MHz, and the low-order channel overlapped the frequency assignment of Channel 13. Bummer!
4. Access. Mt. Hebo was one of the peaks of the Coastal Range and rose more than 3000 feet just a few miles from the ocean beaches. It was reached by a paved road of 8.5 miles length that wound its way up the mountain from Oregon Hwy 22 in the town of Hebo. All the materials for the new radar facility would have to be hauled by truck/trailer up this winding access road, the top 2.5 miles of which was usually covered in ice or snow during the Winter months.

That installation at Mt. Hebo had many "special" features that made it different from any of the other AN/FPS-24s:

1. The instability of the mountain structure required massive infusions of concrete grouting to stabilize it enough to build the radar tower at all. More of this was required when the support structure for the first radome was built.
2. The radar building was specially modified to use corrugated steel walls instead of the thick poured concrete outer walls otherwise employed--again due to the limitations of the mountain itself.
3. When the antenna was completed and the Commander observed ice falling from the tips of the antenna sail and striking the ground below, he asked me if he should order hard-hats for the Operations personnel. I made some hurried calculations and concluded that when the radar antenna was rotating (tip speed = 23mph) the ice would hit about 50 feet out from the walls and would be traveling 100mph when it struck the ground. I told the Commander I doubted that hard hats would be much help. I believe this was the chief impetus for the project to erect the network of personnel walkways in the Operations Area surrounding the tower base. A similar, though lesser, risk would occur from ice simply sliding off a radome and hitting the ground.
4. The Mt. Hebo installation included an additional main antenna drive motor to better buck the high wind loading expected. Also, a special "servo stow" feature was installed, whereby an additional anemometer was connected 90 degrees out of phase and was used to control the maintenance antenna drive system to edge the sail into the wind when the wind speed exceeded design parameters (50 knots).
5. The antenna reflector was made up of special aluminum sheeting pierced with 2" square holes bounded by 1/8" web strips instead of the less open construction used at other locations. This was an obvious attempt to counter some of the effects of the wind loading expected at Mt. Hebo. This was deemed essential, even though it was known that the antenna beam pattern would suffer a little from this treatment. I think that it was also hoped that this more open reflector material would not load up with ice as quickly and that this, too, would improve the ability of the antenna structure to endure the rigors of the Mt. Hebo Winters. Be that as it may, the antenna reflector did accumulate significant layers of ice and on at least one occasion (I was there) the Commander broke out shotguns from Special Services and several people (including the Commander) repeatedly shot at the antenna to knock off some of the ice. It was hoped that enough would be dislodged to positively affect the wind loading, and that the large openings in the reflector skin would reduce the risk of damage by shot pellets. As near as we could tell, there was no significant damage by the shot, and the antenna did withstand the wind storm, so I cannot say that the idea did not work. I had counseled the Commander that I was not sure the idea would do any good, but I also could not tell him it would not--it was his decision to proceed, and the results speak for themselves. I had agreed that it was unlikely that the shotgunning would harm the reflector--covered with ice as it was--and it appears that this was also a correct conclusion. One of my pictures does show the antenna following this interesting activity.

Once the debris had been cleared away and the antenna repaired, it was operated in reduced capacity during those periods when weather permitted (winds of less than 50-knot speeds). Those satisfactory conditions did not exist on Mt. Hebo during most of the Winter season.

When Spring returned in 1963, work on a new radome commenced and, since the support structure was complete and relatively intact, it was possible to complete the assembly of the dome this time and everyone expected the problems to be behind them. Unfortunately, the weather at Mt. Hebo had another trick up its sleeve--lightning. Naturally, the radar antenna within that dome presented a large metallic entity which was very well grounded, and in the Fall of 1963 the antenna was struck several times through the radome by lightning, damaging many panels and opening a large gap to the forces of the wind, which then entered the dome and destroyed it a second time.

Some of the accounts I have read about the destruction of the first 2 radomes, both of sandwich construction, have said that one was destroyed by fire. I don`t believe that is true. I know for a fact that the original uncompleted dome was destroyed by the force of the winds and nothing else was involved. The second dome did suffer lightning damage, which possibly did involve some minor fire damage (I don`t know), but, again, the main destruction was caused by the severe wind forces which were so prevalent at that location.

As you know, a third and successful radome was constructed at Mt. Hebo, this one of space-frame construction and again, everyone believed that the winds had been conquered. Eventually, though, nature had its way again--that radome was not able to resist the Bernoulli forces (lift) of the high speed winds passing over it and it ultimately succumbed to the continued stresses that resulted.

Having been trained as both a Radar Maintenance Officer and an Electronic Countermeasures Officer on the AN/FPS-24 radar and having seen first-hand the absolutely unbelievable video it supplied to the Portland Air Defense Sector, I deeply mourned the necessity of scrapping the -24 and putting a -27 in its place. Fortunately for me, I had been transferred to Cartwright AS, Labrador and other assignments before that occurred. There was something both grand and wonderful about that radar set--the sheer size of everything about it was so "American"! (Even "Texan"!) The antenna "sail" was more than 120 feet across and 50 feet high; the rotating part weighed 70 tons, if I recall correctly. The only piece of waveguide was a unit about 10 feet long (you could sit up in it) used to connect the radar power from rigid coaxial lines (9" diameter) to the feed horn, which itself was 9 feet tall and 6 feet wide. The need to use "chirp" (pulse compression) required an amplifier chain which could accurately reproduce a complex signal with specific frequency characteristics: the final amplifier tube was a triode, with 96 elements contained within a single glass envelope in order to withstand the enormous power potential in use. The filament supply for that tube produced 1.75 volts at 6700 amps (!). For safety, this power was conveyed by large bus bars protected from accidental access by steel cages-that much amperage would just vaporize a wrench or other metal object in a violent explosion. The radar was dual-channel, each producing about 5 megawatts peak power (250 kilowats average), and birds were observed to veer wildly about when they happened to fly through the local beam. I presume the microwaves produced enough instant heat to disrupt their "navigational" senses.

I recall an anecdote from shortly after the AN/FPS-24 radar was declared operational and was providing the search feed to POADS. I was down in the Operations Area one evening when the POADS Air Surveillance Officer called to complain about the radar and wanted to know what was wrong with it. He indicated that there had only been 3 radar blips reported during each of the last several scans. (The previous radar, a fixed-position AN/MPS-11, typically flooded the system with 500 or more, mostly false, hits per scan, most of which had to be screened out by the clutter mapper.) I checked the radar displays myself and they appeared fine to me. I asked the ASO how many planes were in our area at that time and he replied "one", to which I responded "so what`s the problem?" In fact, we were tracking his single flight very strongly, even within the MTI region (which was extensive at Mt. Hebo). In fact, the AN/FPS-24 radar presented a raw radar display that rivalled what SIF would produce--it could track a T-33 inbound or outbound to PRF-limited range. You have never seen such clear radar! It was just beautiful. Part of the reason for the clean display was the combination of very low frequency (P band), long PRF (333/sec), and state-of-the-art double-cancellation MTI; the very strong pulses produced by the 18:1 pulse-compression transmissions ("chirp") also contributed to this clean presentation. The MTI just did not process any fixed clutter or even "angels" (ocean wave clutter)-if something was not moving at least 30 knots radial to the antenna it just did not register in the MTI.

Regards,
Dave Casteel
First RMO of the AN/FPS-24 at Mt. Hebo AFS