If you ever drive around an airport, you may find a low, flat, one-story building. The odd thing is this building has a mini space capsule-looking thing on the roof. I have found many of these buildings - all built the same - at some private airports, as well. And, I have found them in open fields. In remote locations, a small, unpaved road will lead up to the building which is typically surrounded by a high fence crowned with barb-wire. Also, a little weather station is there, too.
Most odd: A friend of mine works “Search & Rescue” at a major US airport. He gave me a personal tour of the grounds (including driving the runways…timing our crossings between planes! Anyway, I saw this building, and he (who knows every inch of the airport) says he couldn’t tell me. Hmm…
This was all mucho pre 9-11-01, by the way. I can make an educated guess what the secret is, but maybe some Doper has observed these buildings, too…and knows the straightdope?
I worked on them when I was in the Navy many moons ago. They are TACAN (TACtical Air Navigation) antennas. They provide navigation information for pilots of all types of aircraft. They also dispense weather and hazard info. I am sure an experienced pilot will be along soon that knows more about them than I do.
It’s probably a VOR (VHF Omnirange) ground station. (VHF = Very High Frequency, which is something of a misnomer as the frequencies used are around 125Mhz – not all that high.) Some of them incorporate a signal called DME (because it’s used by Distance Measuring Equipment). The Military version incorporates TACAN (the device is then called VORTAC).
It’s basically a navigation beacon used by aircraft. The receiver in the aircraft gives bearing (and sometimes distance) to or from a selected ground station. Most sizeable airports have one, and they are also found in the countryside.
There’s a photo at: http://users2.ev1.net/~kb5oqk/omni.htm
Although the civilian (VOR) and military (TACAN) systems use different frequencies and transmitters, the antennas are usually co-located on the same facility. Both technologies transmit two signals: a regular, omnidirectional pulse, and a rotating directional signal with the same period of the pulse. The VOR or TACAN receiver in an airplane counts the difference between the time the pulse and rotating signal are received; from this, the bearing from the antenna is calculated by on-board electronics.
Here’s an analogy. Say there’s a lighthouse with two lights: a strobe that flashes once a minute, and a rotating beam that also rotates once a minute, and passes clockwise through north at the moment the strobe flashes. A ship sees the strobe flash, then counts 30 seconds before seeing the rotating beam. Therefore, he knows he’s at 30/60 = 1/2 of a circle clockwise from north, or due south.
Every answer here has been correct…what you have seen is a VOR or VORTAC station. When I was teaching students in pilot training I would make sure to ask them about that while waiting for takeoff…there is nothing worse that a pilot who doesn’t know what a VOR station looks like.
BTW, the OP mentioned that he can make an “educated guess” as to what the “secret” is of these buildings.
Or are those just more antannaes? Or is it so the pilot knows WHERE the signal is coming from reletive to where they are heading. Although that wouln’t make a huge difference until you were fairly close to landing I’d imagine.
JoeyP by nature of a VOR/VORTAC the pilot knows where the signal is coming from - it’s coming from the station. This may not seem important, but it really is.
As for all those devices surrounding the VOR, I’m not sure. They are not lights, since a VOR doesn’t need to be lit (other than to prevent some guy who’s mowing the airfield grass at night from hitting it). I think they must be some sort of reflecting/calibrating surface that the rotating part of the VOR uses to maintain its timing. This is just a guess of course, since I know how to fly off of VORs but I don’t know how to maintain them!!
The truth is no one has been able to I.D. these buildings for me. One is located amongst all the farmland in Western Md. I know some of the locals quite well, and they all know the people and everything there is to know about that area like the back of their hands. And, although they knew about the weird-looking building, none had a clue what the heck the thing is.
Also, perhaps coincidentally, the building is in close proximity to a satellite tracking station (property of the Federal Government). The antenna is highly visible, but very well hidden if you try to find an access road to the tower. Perhaps, it was a leap of faith to suspect there was some top secret relationship here. Furthermore, I found one by a nuclear plant in PA, allowing my suspicions to run wild. :dubious: