Date:         Tue, 21 Jan 1997 17:01:20 +0200
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         zeidler@NTCNTG02DU.ntc.nokia.com (Zeidler Helmut NTC/Dusseld.)
Subject:      Re: CB antennas


>> Just to have a last word on the antennas.  The glass mount CB antenna 
that
>> Sean intalled will not get out "forward and to the right" as he said.
>> Location of the antenna is not influenced by the vehicles body unless is
>> uses the body as a "ground plane".  And that means that the antenna must 
be
>> attached to the metal of the body.

I agree on this.

>> The glass mount doesn't need a ground plane, so therefore the reception
>> will be omni directional, and the body of the van will BLOCK the signal
>> going to the front and left.

Glass mounted SW antennas mostly have resonant coax cables. Don't cut
them to your needs. This is to match the 50 Ohm output of your transceiver.
Every antenna mounted on cars have preferred directions. But blocking a
signal on CB waves is not possible on cars. Even hand helds are working
inside, of cause with a high loss of field strength. The glass mounted
are working on the same principle as the antennas for fibre glass boats.

>  Sorry to disagree but the wave length of a 1/2 wave CB antenna is 18
>  feet. The body is 9 feet

The body is not in resonance with the wave. The body should reflect the
antenna in that way you get a virtual dipole which is resonant with the
wave length. But a car is a little bit small for an 36 feet wave and it will
be a compromise. The body presents a capacitor against earth and this will
change by moving the car.

>  and the antenna is 9 feet making a total of
>  18 feet. This is called a 1/4 wave antenna. Anything smaller has
>  what is called a base

Not only base loaded but also top or midsection loaded ....

>  load, (a coil), that simulates a 9 foot antenna.
>  Therefor placement of any CB antenna is very important!

Helmut
'80 Camper