I think the larger problem is a lack of standardization in receive antenna systems for broadcast FM.
The late 60s/70s brought along ignorant antenna designs, like the windshield-integrated dipole and the 45-degree swept-back dipole. Now we've got even more ignorant designs like the 45 degree stubby on the roof of cars (06 or newer Hyundai Santa Fe is a good example of this mistake), or oddball angled foil designs in/on window glass (01-05 Hyundai Santa Fe is a good example of this). Absolutely worthless for any linear polarization. Amusingly, on the 01-05 Santa Fe, Hyundai decided to integrate a 10 db-ish RX amplifier in the back near the antenna. It also doesn't have any input filtering. Transmitting on VHF anywhere near the vehicle with any bit of power at all absolutely slaughters any FM RX you might have, even when listening to 50kW + LOS transmitter. AM Broadcast is the worst, where all you get to hear is fuel pumps, alternators and ignition... JS Al Wolfe wrote: > > > Back in the late 60's or early 70's we tried this on one of the stations > I was involved with. CP can work with separate antennas but only if the > vertical and horizontal elements are in the same vertical axis and fed in > quadrature or 90 degrees out of phase. And the SWR needed to be > absolutely > flat, as in 0 reactance or the circular polarization and its benefits > were > negated.. The results at the time showed some improvement in our mobile > coverage but there was a three db hit in general using the same > transmitter > set up as before the CP experiment. The project was eventually abandoned. > > Later the "roto-tillers", cycloid dipoles, and vees were developed where > the circularity was supposedly inherent to the antenna design. I > personally > like the roto-tiller type as they seem to actually generate a circular > pattern with the vertical and horizontal radiation and circularity being > fairly predictable. > > A lot of broadcasters consider circular polarization as a legal > back-door method of doubling your ERP. It's pretty much the standard for > most FM broadcasters anymore. > > 73, > Al, k9si, retired, mostly > > > Years ago before CP antennas were commonly available, FM stations would > > feed two separate antennas on the tower. One >was H, the other V. Was > > that then 45 degree polarization?? > >
