On Sat, 26 Feb 2005 17:33:20 -0500, "Ed Huntress"

wrote:

If I understand it correctly, (which I doubt ), since the car doesn't
act as the ground plane, the ground must. If this so, how come a car
radio that worked very well at recieving faint stations, hardly picks
up anything when I tried to use on the bench with a regular car
antenna? The antenna was connected properly, with the cable plugged
into the radio and the antenna mounting screw connected to the ground
screw on the radio.
Thanks,
Eric

"Robert Swinney" wrote in message
...
Ed,
You're on it like a cheap suit! A ground plane must have an area at least
1/4 lambda ^2 to be effective. The top of a car doesn't have sufficient
area to work as ground plane at broadcast freqs.

Yeah, it would take one hell of a car. And an effective radiator would be
tall enough to wipe out the power lines wherever you drove, while the ground
plane would wipe out the utility poles on both sides of the road. g

Essentially, ground plane
radials provide an artificial ground that is elevated to the effective
height of the antenna wherever it is above earth. It is generally
understood when we speak of "ground plane" re. communications antennas we
are referring to 50 ohm antennas.

Thanks, Bob. It's good to hear that antenna theory didn't invert itself
since I studied for my 1st Class Phone license.

I'm not following this thread very closely but it sounds to me that some
people are mixing up transmitting-antenna theory with receiving-antenna
theory. A car antenna is just a conductor stuck up there to suck up as much
electromagnetic radiation as possible. Some of them are loaded at the base,
but I always assumed that was for FM. 'Don't know for sure.