Photos by Rick Thompson A wingtip rotates on a mechanical arm in one of the FARM’s two anechoic chambers . . .

Welcome to life down on the FARM.

Not the farm, lower case — Bob Evans and his descendants are nowhere to be seen — but the FARM, all capitals. It stands for ‘‘Facilities for Antenna and RCS Measurement.”

FARM is actually a three-level acronym, because ‘‘RCS” stands for ‘‘Radar Cross Section,” and ‘‘Radar” in turn is a pre-World War II acronym for ‘‘RAdio Detection And Ranging.” Time has reduced it from all capitals.

All grammatical fun aside, the business of what is called at Pax River the ‘‘Antenna Farm” is deadly serious, for antennas are the extended eyes and ears of modern aircraft.

‘‘We try to determine the effects of the aircraft on the antenna itself,” said Dennis DeCarlo, chief antenna systems engineer at the FARM. ‘‘The aircraft acts as a ground plane (the surrounding surface where it is mounted) for the antenna, and it affects the transmitting and reception patterns of the antenna.” Using his pen as an example, he said, ‘‘An antenna can have one set of characteristics installed at one place on an aircraft,” then moving the pen, ‘‘while at another place it works much better or much worse.”

The aim is to find that ideal placement before the process gets very far along. ‘‘If they find a problem after testing in flight has started, it takes time and money to correct it,” said DeCarlo. ‘‘They might decide to take the risk and live with degraded performance. Our job is to see they don’t have to by catching the problem early.”

That’s one of the reasons they put aircraft up on towers, frequently upside down. RF signals are transmitted at the antennas while they are attached to the test aircraft. If the antenna is on the underside, the aircraft on the tower has to be turned upside down. The reason is simple: If the aircraft is right side up, the huge mounting tower will interfere with the antenna’s reception. Aircraft don’t carry huge towers while in flight. ‘‘Our job is to determine where to put the antenna itself, and we have to measure its field of view,” said DeCarlo.

The towers could be a story unto themselves. Each of the aircraft weighs 10 tons or less. The towers can handle a vertical load of 22 tons. The mounting mechanism can turn the aircraft left or right, lower the nose or raise it — basically, any position it would have in flight. At any position, the antenna’s reception can be monitored.

The FARM has an F⁄A-18 and F⁄A-18E Super Hornet, an EA-6B Prowler, and an H-60 helicopter, which means it can test in a wide range of real-world situations — especially when coupled with computer modeling.

There is another advantage to having an actual aircraft on a tower. ‘‘We can get an antenna at a very early stage of development, when it is just a delicate laboratory model, maybe just a few pieces of copper soldered together,” said DeCarlo. ‘‘Put that on an actual flight and it wouldn’t survive takeoff.”

Multiply the work done on one antenna by the sheer number of them on naval aircraft — a platform such as the P-8 will carry more than 100 different antennas, according to DeCarlo — and the frequencies on which they operate — from the mid-kilohertz to the high gigahertz — and the changes made on the aircraft themselves, and the FARM has enough work to stay very busy.

Helicopters pose a special problem: whirring rotors overhead. They can cause interference with antennas receiving signals from above (example: GPS), because they continually break the ‘‘line of sight” overhead. Signals from other directions are also bouncing off those rotors. These problems are in addition to those that would be faced if the H-60 were a fixed-wing aircraft.

Technicians recently installed a mechanism that will turn the rotors on the H-60 to test the effects of those rotors. They have also come up with a unique improvisation for initial investigations in this area: a commercial ceiling fan installed directly over a test antenna. The fan can be sped up or slowed down to test how the antenna reacts to different speeds.

It’s not just the antenna that has to be tested, especially if it is not exposed to the air. If in a dome or other cover, that has to be tested, too. (If it isn’t covered, that’s a whole other set of concerns with a whole other set of tests.)

One test of a radome is whether it will survive the flight, and for that the FARM has a decidedly low-tech tool. Its top and bottom used to be the ends of a decommissioned ship’s boiler. A piece of radome material is put inside on an arm that spins at high speed as water is sprayed. It simulates that piece of material (usually plastic) being hit by rain as the aircraft flies at high speed.

‘‘Those problems were discovered during the Vietnam era,” said DeCarlo. ‘‘Radomes were coming back from missions full of holes.” The device, which can also be used to test the durability of paint, is unique. ‘‘There’s nothing else like it in the Navy,” DeCarlo said. ‘‘We don’t use it often, but you have to have it when you need it. Nothing else does that job as well.”

In addition to durability, a radome must be transparent to the antenna’s radio frequency, which is why that previously-mentioned wingtip is rotating slowly. On the end of the wingtip is an antenna; the plastic protecting it is the subject of the test.

The wingtip is mounted on a mechanical arm in one of the FARM’s two anechoic chambers. This chamber is 40 feet wide, 40 feet tall and 100 feet long. Its brother in the next building is somewhat smaller and tapered in a cone shape. Both are lined with carbon cones that absorb radio waves. They also absorb sound waves, so there’s no echo in the chamber.

The result is that the only signal the antenna receives is sent by a transmitter near the technician, Brandon Nickisch. Nickisch knows how much signal is being sent, and the computer is telling him how much the antenna is receiving. At the end of this test, he will know if the plastic is transparent to the antenna.

If it isn’t, maybe another material will work. ‘‘They’re always changing things,” said DeCarlo. ‘‘There may be a new requirement with a different antenna, and the same mounting may not work with the new antenna. There are things we can do that could never be done in flight, and we can do them in a well-controlled environment.”