On Thu, 02 Mar 2006 19:35:15 -0500, Amos Keag
wrote:

Cecil Moore wrote:
Dan Richardson wrote:

Roy is quite correct in stating that a vehicle's body behaves as one
side of a dipole. A lopsided dipole to be sure, but one half the
antenna just the same.


Seems the truth might lie somewhere in between. If the ground
plane of a vertical antenna is near the ground, there are
losses. If the ground plane of a vertical antenna is located
1/2WL above ground, the losses are a lot less. I'll bet that
if the vehicle were located 1/2WL in the air, the efficiency
would increase.

Kind of tough though going under power lines, bridges and overpasses :-)

That depends.... If you take cecil up on his idea, you may go over
them.... of course, that you may want to be on the low bands when you
cross some bridges....
--
73 for now
Buck
N4PGW

"Buck" wrote in message
...
On Thu, 02 Mar 2006 19:35:15 -0500, Amos Keag
wrote:

Cecil Moore wrote:
Dan Richardson wrote:

Roy is quite correct in stating that a vehicle's body behaves as one
side of a dipole. A lopsided dipole to be sure, but one half the
antenna just the same.



Not exactly. Body of the vehicle behaves more like a ground plane and a
capacitor coupling to the ground. As soon as "radials" or ground plane has
antenna mounted somewhere else than on the edge, you get cancellation of
current along the body - two sides "working against each other". We are
talking vertical antenna here, not a goofy dipole.


Seems the truth might lie somewhere in between. If the ground
plane of a vertical antenna is near the ground, there are
losses. If the ground plane of a vertical antenna is located
1/2WL above ground, the losses are a lot less. I'll bet that
if the vehicle were located 1/2WL in the air, the efficiency
would increase.


Depends. If vehicle is going over metal grid frame bridge or good ground,
like salty beach, the efficiency goes up. Body of vehicle is like a plate of
capacitor, coupling the ground plane to effcient ground and performance of
the vertical goes up, especially at low angles. Drive over the bridge or
ocean beach and see the S-meter go up.

Kind of tough though going under power lines, bridges and overpasses :-)

That depends.... If you take cecil up on his idea, you may go over
them.... of course, that you may want to be on the low bands when you
cross some bridges....
--
73 for now
Buck
N4PGW

Yuri, K3BU

On Thu, 20 Jul 2006 17:11:10 -0400, "Yuri Blanarovich"
wrote:


"Buck" wrote in message
.. .
On Thu, 02 Mar 2006 19:35:15 -0500, Amos Keag
wrote:

Cecil Moore wrote:
Dan Richardson wrote:

Roy is quite correct in stating that a vehicle's body behaves as one
side of a dipole. A lopsided dipole to be sure, but one half the
antenna just the same.



Not exactly. Body of the vehicle behaves more like a ground plane and a
capacitor coupling to the ground. As soon as "radials" or ground plane has
antenna mounted somewhere else than on the edge, you get cancellation of
current along the body - two sides "working against each other". We are
talking vertical antenna here, not a goofy dipole.


Seems the truth might lie somewhere in between. If the ground
plane of a vertical antenna is near the ground, there are
losses. If the ground plane of a vertical antenna is located
1/2WL above ground, the losses are a lot less. I'll bet that
if the vehicle were located 1/2WL in the air, the efficiency
would increase.


Depends. If vehicle is going over metal grid frame bridge or good ground,
like salty beach, the efficiency goes up. Body of vehicle is like a plate of
capacitor, coupling the ground plane to effcient ground and performance of
the vertical goes up, especially at low angles. Drive over the bridge or
ocean beach and see the S-meter go up.

Kind of tough though going under power lines, bridges and overpasses :-)

That depends.... If you take cecil up on his idea, you may go over
them.... of course, that you may want to be on the low bands when you
cross some bridges....
--
73 for now
Buck
N4PGW

Yuri, K3BU


Thanks for the reply, I suppose you figured out I was playing on
Cecil's reply.

Tonight, I did have a related experience. I have an FM BC band xmtr
in the car attached to my CD player. I use it to monitor the cds on
the car stereo. I noticed tonight when I crossed a very high bridge
that Radio signals drown out my little monitor transmitter, only while
I was on the bridge. The car was specifically over 1/2 wave above the
highway below it.

for what it's worth....


Buck

--
73 for now
Buck
N4PGW