This antenna is a slight misnomer. It actually is a vertical half rhombic with a termination resistor to make it mono-directional.
Another ex British military antenna, I bought this for the VHF Clansman PRC351/2 for a bit more gain over the standard ground spike antenna or its elevated counterpart. I also thought that if it turned out to be more hassle than necessary I would use the wires to make other antennas.
So, what is it and how does it work?
It is basically a wire antenna of multiple wavelengths designed to be used with a Racal 12m mast set to 9m. The primary wire is 44m long and is fed from a balun at one end and terminated with a resistor at the other. To eliminate variances in ground conditions, a second wire is run between the balun and resistor at ground level to act as a counterpoise. Because the antenna was designed for military use it all is made from very heavy duty components, the wire is Kevlar reinforced and both the balun and resistor will be severely under rated. The design specifications say that it is designed for a frequency range of 30-80Mhz with a power handling of 75 watts.
Well, how does it perform? I don't know yet! This year has been awful for weather. I have not had a chance to actually get out with the mast and antenna yet so haven't yet tried it out. The other problem with it compared to the Elevated Ground Spike Antenna is the sheer size of it. 100 feet long and 30 feet high. I will be trying it out though and I have also been doing some research on half rhombic antennas which seem to suggest that the antenna will work on any frequency where it is over one wavelength. I will set it up and actually put an antenna analyser on it to see what its range is. My own calculations seem to say that it should work from 40m through to 2m. There is a version of this issued to US forces which is double the size and that is specified to work at HF frequencies from 2Mhz so mine should theoretically be usable over a wider range than specified by the paperwork.