Ivan's suggestion is a good one, but not everyone can afford the types of antennas that they sell and / or want such a large directional antenna. All of the info that i've presented comes from both verifiable sources and well over 20+ years worth of reading and experimenting with RF / various antenna designs.
Personally, if i wanted the "ultimate" in performance, i wouldn't be looking at ANY Yagi antenna i.e. the design that Antenna Performance uses for their top models. The cubical quad is the only way to go IF looks and / or convenience are not a factor. While it is a higher maintenance design, the gain on the cubical quad is appr 66% higher than a Yagi of identical element count. As far as i'm concerned, a 66% gain in performance while retaining the same appr boom length is a "no-brainer".
As far as building your own antenna, modifying existing designs for better performance or optimizing the mounting location of what you already have, i would suggest picking up a copy of the American Radio Relay League's ( aka ARRL ) "Antenna Handbook". This book is worth its' weight in gold to those that like to tinker with such things. If you would like to do any of the above but don't want to become a long-term "antenna engineer" i.e. make the investment in this book ( probably well over $30 ), you can probably request a copy of this from your local library. This book has tons of different designs, explanations, formulas, etc... As far as the products that the folks at Antenna Performance make available to the public, i'm quite certain that the basic designs and the design principles can be found within this book.
As far as antennas go, my personal experimentation with both commercial and home-brew FM antennas has shown that a resonant 1/4 wavelength ground plane is hard to beat when mounted out in the open. As luck would have it, such a design is both easy to make and small in stature. If you've ever wondered why you can pick up stations in your car that you can't hear real well in your house, that is because the antenna on your car is pretty much what i just suggested i.e. a 1/4 wave resonant ground plane. Now picture the same antenna performance of your car mounted 20' - 40' higher with nothing around to obstruct the signal and you'll have some idea of what i'm talking about.
A 3/4 wave ground plane will also work well, but is both harder to make and support and three times as large. Any other wavelength will require more effort to build and will be more complicated to design. I'm specifically referring to the use of loading coils, baluns, etc... Such a design may not be as efficient depending on how those elements are constructed and implimented into the design.
There are many different ways to construct a ground plane, but the easiest is to have one vertical radiator for the "hot" with three or four radiators making up the "ground plane". If this sounds familiar, it is because it probably is. Such designs are very common-place and what were used for CB base antennas in the past.
For FM use, the vertical should be appr 30" long for "middle of the band" tuning. If you want better performance at the lower end of the FM band, make the vertical appr 32" long. If you want better performance at the top end of the band, make the antenna 28" long. The bigger the diameter of the element used for the vertical, the better off you'll be in terms of wide bandwidth and picking up more stations.
All of the ground radials should be of appr 32" long and should be fanned out evenly around the base of the antenna. The radials can be arrayed so that they stick straight out horizontally or droop at a 45" angle. One approach may work better than the other depending on mounting height, surrounding objects and the terrain in your individual area.
This design works FAR superior to the Magnum / Metz / Fanfare model and smokes several other commercially available models that i tested. The tuning of the antenna is far more resonant and maintains that tuning over a much wider bandwidth than the Magnum / Metz / Fanfare models. What this translates to in plain English is better reception with the ability to pull in more stations with a lower noise floor. After all, there is a reason why so many manufacturers choose this style of antenna in the communications market. Efficiency, ease of construction and "reasonable" size are three prime factors.
With the above in mind, it is beyond me why antenna manufacturers haven't produced such a design for the FM market ??? I had plans to do this very thing, but just haven't gotten around to it. I have built several prototypes, done a lot of testing and come up with a finalized design, but coming up with specific parts that i need to sell these on a higher volume basis has been a problem. I may still end up doing this if i can get my act together. Once again, i've got more projects to tackle than motivation to get them done. Maybe if i logged off the puter more often and..... : ) Sean
>
