Interesting discussion and everything appears factual. I spent almost my whole career as a broadcast engineer and did both FM and TV. Early on FM was horizontal only same as TV. That way you could use your TV antenna to receive FM as well. As time went by FM radios started appearing in vehicles and portable radios with whip antennas as well. Now FM was faced with the dilemma of serving both home receivers hooked up to a TV antenna and the new mobile and portable radios. That's when CP came into the picture. CP receive antennas also have decided advantages if the transmitted signal is CP. Forgive me in not remembering specifically what the advantages were but I remember only reading that they were there but in spite of that CP receive never caught on. CP never caught on with TV as well although there never was the compelling reason to use CP. Economics had a major part to play in CP or not CP. Economics plays the same role in the two way industry as well. We're in the same boat they are and maybe even more so. Many of us are fortunate to be able to have a repeater in operation using older surplus commercial equipment. My repeater is an old Micor which just keeps running and running. Now, enough of the history. Some have mentioned directional CP. Shivley and ERI (I think) offer directional CP FM broadcast antennas. They use a parasitic element with their standard CP antenna. As I recall they can get at least a 10 dB null on the tower side of the antenna. Another option is to use crossed dipoles with appropriate phasing harness. Scala makes them and I used an array of two on a translator that was shoehorned in between two other stations. There's advantages to each type of polarization but we end up living with standards set years ago. It's not unlike analog TV. We lived with NTSC color (sometimes refered to as "never the same color") when the European PAL standard was much better.