Most of the FM stations broadcast circular polarization, but it seems
that more of the hoz part gets attenuated by trees more than vertical.
So if there is a shallow angle to the transmitter, through some vegetation
Vert seems more dominant.

But I think this changes with over-the-horizon, and it gets more Hoz,
but I have not measured this.

On the original question, you can add antenna patterns if they are phased
right.
You can put a piece of metal in the direct path to block signal, may go down
10 dB or so.
Metal could be screen wire mesh between dipole and unwanted transmitter 10
by 10,
centered to get phase null in the back.



"JGBOYLES" wrote in message
...
I thought the FCC required equal EIRP of both vertical AND horizontal
polarization for an FM broadcast station? Did the horizontal requirement
get
deleted?

I don't know, just reporting on the results of my tinkering, I get by far
the
best signal with vertical polarization. I assumed that was becuse they
wanted
to target automobiles. Maybe the EIPR of the stations in both the
vertical
and horizontal planes in my area are not in compliance?
73 Gary N4AST