Check out this short read:
http://iris.nyit.edu/~sblank/VPforFM.htm
Check out this short read:
http://iris.nyit.edu/~sblank/VPforFM.htm
Explores the theoretical advantages of vertical FM signal propagation. Some of it makes good sense to me ... because it's very true that the largest audience of FM radio is mobile, i.e., in vehicles, virtually all of which, for practical reasons, have vertical receiving antennas.
Some local FM stations here recently relocated to a much higher elevation using lower power and vertical antennas.
They probably lose in building penetration but gain distance for vehicle reception.
Also their electricity bills go down greatly.
Both of the vehicles at the 8Z household have the radio antenna embedded in the glass and the conductors run in the horizontal direction which implies horizontal polarization.
My vehicle's antenna system is a space diversity setup with an antenna in each of the two rear side windows. They trace a rather interesting pattern which looks as if they are designed for both horizontal polarization for FM and vertical polarization for AM. I am not sure if this is a true diversity system or if the antennas are just paralleled with a balun or some type of combiner. Things aren't as simple as they once were.
The vehicle has a keyless entry and ignition system which is an interesting application of Part 15 stuff. It is a challenge/response system where the vehicle interrogates the fob on 125 kHz and the fob answers on 315.2 MHz. Range is 1.5 meters.
Combined with my AM and FM operations, remote temperature and rainfall monitors, telephones, and wifi our abode is awash with Part 15 signals.
Neil
Hi Neil and everyone at Part 15.us
Your antenna system on both vehicles sounds nearly identical to the one in our 97 Pontiac Transport. Except I am not so sure about the rear window having any antenna embedded in it, but i may be wrong.
In the front windshield there is a folded dipole i guess which is as you stated horizontally polarized, but what about the rear window?
Since the Transport has a rear defogger which is electric (it has a separate switch) it has wires running vertically up the sides of the back window then horizontally across the same window. Would it be possible that I have the same system?
I am really not sure but i do know my reception seems to be very good on the factory GM cassette stereo system. I hardly lose a strong station and I can pick up noisy signals if i was sitting in a open area and turned my minivan around until the signal improved.
When I was heavy into CB Radio, I had a horizontal dipole in the yard wired into a switch along with a home brewed quad beam, oddly enough when signals were hard to copy on the beam i could switch to the dipole and catch the stations i was trying to hear.
Our atmosphere does some strange things to a signal , besides acting like a mirror and bouncing the signals, they are also changing from vertical to horizontal. This is what helped me receive some weak signals across the globe on SSB which was one of my favorite modes to work.
I think the correct term for that is Dual Diversity