Best Omni Antenna?

[MarkGL]

I know this forum is intended for radio monitoring, but it looks like many of you are very knowledgeable in all aspects of antenna design, and I'm looking for the best omnidirectional antenna I can find for transmitting. I'm helping to design an LPFM station in Florida. Frequency will be 102.7MHz with a 100 watt transmitter. The surrounding terrain is very flat. The antenna will be on the top of a 12-story hotel, and we have a limited budget so I was hoping to go with something we could construct ourselves. I thought a j-pole would be ideal, but a different thread on this forum has me reconsidering that. Would a simple 1/4 wave ground-plane work best? Is it worthwhile trying to make a 5/8 wave ground-plane instead? I don't really understand how to match that to a 50 ohm coax feedline - a coil of some type is apparently needed. Is there some other omni antenna I'm leaving out? How about those vertical CB antennas that have three sections, are about 18 feet, and are classified as "1/2 wave over 1/4 wave"? Are they any good, and is it possible to DIY one for this frequency?

Sorry for all the questions. Basically it comes down to this: What's the best omni-directional antenna I can construct? Thanks.

 

[rfradioconsult]

Don't even consider a homemade antenna for a LPFM station. You are starting out ar a disadvantage by competing with regular FM stations. Most FM stations use dual polarized antenna that radiate a verically and horizontal polarized signal. I haven't read up on LPFM but regular AM and FM stations have specific field strength requirements to cover their service area. Skimp in other areas but not in the transmitter/antenna and feedline. If no one can hear you why build it in the first place?

Here is a link for a true FM broadcast antenna. http://fmbroadcastantenna.com/

 

[jackj]

rfradioconsult is right. Don't even think about trying to design and build your own LPFM transmitting antenna. I believe that the FCC licenses for commercial FM spec the effective radiated power of the station. One of the aspects taken into consideration in this spec is the gain of the antenna, do you have the needed equipment to measure antenna gain?