A 2005 Chevy Tahoe had a 5 foot (maybe even pushing 6 foot) antenna atop it. This antenna – it had 3 circular hoops protruding from the bottom about 6 inches up. The antenna was situated about ¾ of the way in back of the SUV. The Tip of the antenna was so high off the ground it wasn’t too far from sweeping against the underpasses and was about 6-12 inches higher than the school bus this Tahoe passed.
This looked to be a civilian SUV. In an age when Satellite antenna are almost unobtrusive, even cop’s antennae really aren’t like the 1970’s Smokey whip antenna anymore, I had to wonder:
What was this antenna likely used for? What purpose did it serve to be so GIANT? What did those three hoops do?
Antenna size is directly related to the operating wavelegth. High-frequency short-wavelength signals, like cellular and VHF public service use very short antennas, while low-frequency long-wavelength signals like CB and lowband Ham radio use much longer antennas. It was probably either a CB (11-meter band) or a 6-, 10- or 20-meter band Ham antenna. The “hoops” are probably part of some kind of inductive coupling configuration or ground radials which form part of the ground plane.
Civil Air Patrol uses civilan vehicles (often SUV’s) to look for ELT’s (emergency location transmiters). Transponders from downed general aviation aircraft.
While I’ve never seen an antena like you described, it may be some new fangled one.
If you’re direction finding, you’d use (in most cases, VHF/UHF) a directional antenna, called a Yagi type. It looks similar in nature to a standard home rooftop TV antenna. Doesn’t sound like the OP is describing an antenna of this variety.
More than likely, the large antenna you mention is being used by an Amateur Radio Operator (HAM) for very low frequency use while driving. From the lenght and description, I’m betting the 120M - 80M band range (wavelength in meters, divide into 300 to find the frequency in MHz).
There is a whole culture of HAMs that take LF (low frequency) gear in their vehicles to remote locations, or to work on the commute. There are even guys that will use Morse code in the car!!! WHILE DRIVING!!!
The round rings were likely to present a ground plane for the signal, this causes the signal to radiate more towards the horizion, rather than upward in a cone. Sort of pulls the edges of the cone more towards the horizontal.
I’m also betting it’s some sort of a homebrew antenna, rather than a commercial one, or a very old commercial type, as though I’ve seen this type of antenna before, all of the modern ones use large coils to match the wavelengths, and are much more modern looking in all the links I can find online.
