Re: RF fields and 2-way radios

["George Andrews" <mauser2@erols.com>]

Jillian,
    Can't comment on the mechanism causing the effect you observed. However
a solution to the problem is to move the antenna to the roof of the vehicle.
(The roof serves as the ground plane) It seems like you are concerned with
resale value of the vehicle, so magnetic mount antenna would be the first
suggestion. The most efficient radiator is a 5/8 wave radiator with a
loading coil at the base. Most commercial products cover a wide range of
frequencies and can be tuned to your specific needs. Tuning consists of
cutting the radiator to the appropriate length for the frequency. The vendor
should supply this service. If a 5/8 wave antenna is not available, a 1/4
wavelength antenna is the next alternative. If a model is unavailable for
your frequency, I would suggest the purchase of an antenna designed for 50
to 54 MHz (amateur radio frequencies) and have it cut to the proper
wavelength.
    If you have any further questions, please use mauser2@erols.com. I will
be happy to supply further info or (US) vendors.

George Andrews
-----Original Message-----
From: Jillian.Wright@dtir.qld.gov.au <Jillian.Wright@dtir.qld.gov.au>
To: Multiple recipients of list <radsafe@romulus.ehs.uiuc.edu>
Date: Wednesday, March 04, 1998 1:07 AM
Subject: RF fields and 2-way radios


>Dear Radsafers,
>When tested, vehicles where 2-way antennas were fitted
>on the driver's side fender about 300 mm forward of the
>windscreen had elevated E and H fields produced by
>resonant coupling effects between the steering wheel and
>driver side seat frame. Shifting the antenna to the LHS
>fender made no difference. A vehicle with a bull-bar
>mounted antenna and a truck with a LHS gutter mounted
>antenna (drops the resale value) did not exhibit this effect.
>2-way radios transmitted at a nominal 25W, f = approx
>81MHz.
>
>What is the mechanism inducing the fields between the
>seat frame and steering wheel?  and
>How else can the antenna be mounted so that these fields
>are unlikely to be generated?
>Few vehicles have bull bars.
>
>Thank you.
>Jill
>_________________________________________
>Jill Wright, M.H.Sc., B.App.Sc., MSIA
>Senior Workplace Health and Safety Inspector
>Department of Training and Industrial Relations
>----------------------------------------------------------------------
>---
>Jillian.Wright@dtir.qld.gov.au
>PO Box 317 Annerley QLD 4103 AUSTRALIA
>Phone: 61 7 3896 3419   Fax: 61 7 3393 1869
>_________________________________________
>
>
>