"Steve W." wrote in message
...
"Jerry Martes" wrote in message
news
mTTd.47166$uc.41105@trnddc03...
"Steve W." wrote in message
...
Jim, you are correct. The antenna is the vertical element and the
vehicle is the ground plane. That is why the coax is grounded at
both
ends and one small open area causes noise. Some of the new antennas
are
hidden in the glass with the defroster, or just in the glass around
the
edge. Then there are diversity antennas that have 4 antennas
embedded in
the bumper covers or other plastic trim. Those are connected to a
box
that senses the different signal levels and uses the strongest.
Anyone
who thinks otherwise doesn't know how a radio signal functions.
--
Steve Williams
Steve
I'm surprized that you state that anyome who doesnt accept that the
car is
a ground plane doesnt know how radio signals function.. I assume
that you
agree that the impinging radio signal is vertically polarized. I
asume you
also are considering cars that are only about 1 or 2 electrical
degrees
high. Can a conductor that small (short) be considered a "Ground
Plane"??
I didnt realize that cars had been equipped with an AM antenna
systems
that select one or more of several probes in the trim and/or bumpers.
That
seems to be unnecessary complexity, but it must provide some
improvement.
Where can I find more information on the car that has the 4 embeded
antennas?
Jerry
Jerry,
The chassis of the vehicle is the ground plane of the antenna on every
vehicle I have ever seen. The vehicle height is not how the ground plane
is measured, it is measured by the amount of continuous connected
conductive surface area located around the antenna whip. That is also
why radio stations fade at different amounts based on which direction
the vehicle is headed. The different amount of ground plane relative to
the location of the whip on the vehicle changes the received signal
strength.
AM/FM broadcast signals are both vertically polarized. Have been for a
long time.
Lots of diversity equipped vehicles out there. Most of them are high end
luxury cars but there are a few pedestrian models as well. The town car
is one, Mercedes has a couple as well as BMW and Audi.
If you really want to see a strange antenna system take a look at the
ones used by XM and Sirius. Short vertical antenna to receive a circular
polarized signal that alters its angle of reflection as you move.
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Steve
I used to think about antennas most of the working day. I still couldnt
refer to a car chassis as a "ground plane" for AM radio. It is just too
small. A car is in the vicinity of 1/100th of a wavelength. long, and half
that wide. That seems way too short to be worthy of being referred to as a
"ground plane", isnt it?.
There is alot of car information that has escaped my understanding. I
used to reserve the term "chassis" to describe the frame the cars body
bolted to. But, since that construction method isnt used much any more, I
guess you refer to the metal part of a car when you write "chassis".
You are apparently learning things I dont know about.
I thought we were considering AM radio for car antennas.
When did FM stations go to vertical polarization? I was thinking they
were circularly polarized.
On that "diversity equipped vehicle", do you suppose that diversity is
for satellite receiving antennas? I have problems with trying to imagine
how the radiation pattern at AM could be made directional, no matter where
it got "connected to" by the transmitter (or receiver). The car is just
too small in terms of wavelength to get directional.
You can feel free to use technical terms to tell me how the AM radio
signals are received by a car. There are alot of really well informed guys
on this news group. Even I thought I understood enough about car radio AM
antennas till you showed me that I dont to understand correctly.
Jerry