Truckster (Vic) replied:

Look here for the answer.

http://www.gme.net.au/land/choose_ant.html

TravellingVegemite replied:

The dealer I got mine from recommended mounting on the roof gutter rather than the bull bar so that the car (and caravan) is not in the way of the signal in the rearward direction. It is also better when higher.

Roger

Old Soldier replied:

G'day Rosco,

I would suggest you take note of the link provided by Truckster. For the average usage you will not get better advice.

Re gutter mounting, if gutter mounted your maximum radiation will normally be to the opposite side of the vehicle, so in reality that nullifies the advice to place it there so you can transmit back over the caravan you are towing.

In this position the weakest lobes of the emission would be to the front and rear.

Examples of all radiation patterns are shown in the link from Truckster.

The thing to remember here is that this is all working on the principles of Antenna Theory. and that's just what it is - Theory!!!

From time to time you will get situations where the characteristics of your transmission and reception defy all theories - and take it from a former proffessional radio operator and instructor, that happens more than the theorists would like to admit :) :)

Enjoy the bush

DennisN

Phil G replied:

The radiation patterns are irrelevant when using a ground plane independant antenna. I cannot see any reason to purchase an antenna that requires a ground plane. That leaves one main variable - antenna height, and for identical antennae, a gutter mounted always outperforms a bullbar mounted.

I do a lot of 4wd convoy work, and the bullbar mounted antennae give the poorest range, unless one of those very large, expensive antennae are used.

My recommendation is to use a grount independant base and purchase two antennae to go with it - a short rubber stubbie for around town, and for most bush work and the normal 6 dB for desert or open country work. I end up leaving the stubbie on 90% of the time as it is indestructable and performs extremely well when roof mounted. A swing down base is useful if you intend using the longer 6 dB aerial as well.

Also, the most common cause of poor UHF performance, is poor installation with shorting or core breakage at the plug - make sure its soldered well, and get the shop to do it if you're unsure, or not handy with a soldering iron.

Most roof mounts are best positioned above the drivers door, and the cable is run down the channel and into the cabin thru the rubber taking the wiring to the front door (May not have one on a Landrover!)

Cheers

Phil

Boxa replied:

Ross,

Plain and simple. UHF's mode of tx/rx is LOS (Line of Sight). What you see is what you get. Obviously the higher the better and the more radiation conductor beneath (metal) the better the reception in the opposite direction will be.

It works much the same way as holding someones hand while you touch an electric fence, you feel a tingle while they receive the brunt of it.
The AE is you touching the fence with the furtherist part of the car being the unfortunate shock victum. Mounting the AE on the bullbar will use the entire car to transmit better from behind.

To answer your question,
the more further back you have your AE from the bullbar, the further forward you can both tx and rx.

Its my job, I have to know this stuff.

Happy trails,
Box

Eric Experience. replied:

Ross.
The best place for the antenna is the centre of the roof but if that is not on then a bracket of the spare wheel mount works best on the defenders, make the bracket at a hight which allows the bulk of the antenna to be above roof hight and towords the centre line of the vehicle, it will not be damaged by branches that are at the normal 45degree angle. Eric.