[Antennas] Proximity of Antennae On Top Of Car??

[Dave Shrader]

First of all for the science types: Any metal or conducting material in
the near field will interact [absorb, distort, or couple] with an active
antenna. That said, what are the practical issues?

1) You should have no practical interactions. I use a 706 MK IIg with
hamsticks [40 through 12 meters] and a Larson through the glass for
2/440. No problems. The vehicle physical geometry, roof, fenders, etc.,
will have more impact on antenna pattern and performance than any
antenna interactions.

2) Parasitic excitation, i.e. directors/reflectors, require BOTH near
resonant lengths [typically +/- 5% of the radiating element AND critical
spacing typically 0.15 to 0.22 wavelength. Your setup violates the
length requirements so you should not have any issues.

3) None expected.

73, Deacon Dave, W1MCE
Manager, Textron Antenna Range, retired 
=============

DavidE Benedict wrote:
> 
> Hi All,...
> 
> I am back again after a year or more absence.
> 
> I want to install a 6M vertical on my Subaru stationwagon roof.
> 
> I already have a (Comet?) 2M-440 combo VHF/UHF up there on the roof at the
> center (side-to-side) and slightly forward of roof center (front-to-back),
> and a Screwdriver antenna on the front (passenger side) bumper.
> 
> Surely there must be somebody with practical experience on this one...
> 
> NOTE#1: I use an IC-706, and the 6M and the VHF/UHF feeds are at different
> PL-259's on the back of the radio.
> 
> NOTE#2: The HF Screwdriver antenna and the 6M antenna are fed thru a coax
> relay so that both are never connected to the IC-706's HF/6M RF connector
> at the same time.
> 
> My questions are:
> 1) How much trouble am I in with interaction of these three antennae?
> 2) When I am 6M I wonder if the Screwdriver and/or the VHF/UHF antenna
> might act inadvertantly as a director element if my spacing is wrong...?
> 2) Are there exact rules, or rules of thumb about their juxtaposition?
> 3) If there are possible problems, what are they, and how do I minimize or
> eliminate them and still have these two antennae up there on the roof
> together?
> 
> TIA for any help...
> 
> W7DBH
> David B.
> 
> - - -
> 
> Your moderator for this list is:
> Larry Wilson KE1HZ antennas-owner@mailman.qth.net
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