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The original government studies involving parallel vertical radiators (Folded Monopole), or a cage monopole, was conducted by the U.S. Navy years ago before it was developed for commercial antenna use or patented for commercial use. I used to have a copy of the original study. It was quite revealing. The outcome was that, even though the bandwidth was increased, the efficiency of a single radiator of the same length (i.e. a tower) was essentially the same; all things being equal (radiator, feed system, ground system). The study involved development of the Folded Unipole antenna design. More information on the Unipole antenna system is available here:
http://en.wikipedia.org/wiki/Folded_unipole_antenna
The Star-H, or Kintronics, antenna system is essentially an out growth of the same body of antenna design and theory. The KinStar antenna is used primarily where a tall tower cannot be erected due to height restrictions, usually because of proximity to an airport or heliport (KCST AM). Several Companies construct and sell the Folded Unipole as stock in trade. The Folded Monopole has been used for VHF and UHF communications for many decades. Even a version of the antenna has been published in the “ARRL Antenna Book” for decades. Here is more information for your consumption:
http://ezinearticles.com/?Grounded-Folded-Monopole-Antenna—Tunipole&id=4435064
Because of the physical mass and weight of this antenna design, using it for the purpose of improving the antenna system for the Rangemaster would necessarily cause stress the transmitter casing and possible compromise of the transmitter with moisture. Any perceived improvement to the Part 15 signal would be minimal at best.
I have personally designed and installed 2 Folded Unipole antenna systems with great success. Both of the systems were installed to overcome ground system losses. The ground systems in both stations were either seriously compromised or constructed in soil with next to no conductivity (near pure silica). Efficiency of the system did improve somewhat. Bandwidth was improved as well. The vertical was very near 90 degrees in length in both cases. And, both are still in operation today, after 20+ years of service (KORE AM & KLOG AM).