Member - Banjo (SA) posted:

er....re my above post ...I should check my cyber scribble - that line should read ... vks737.on.net (Offroad Equipment section)....

Member - Roachie (SA) posted:

G'day Smudger,
I think you might have misread the question. asking about "HF" antenna, whereas you mention "UH" which I assume you mean "UHF" (based on your statement that you mount your antenna on the gutter of your vehicle).
HF Antenna's (the auto-tune variety anyway) are the quite large units you'll often see........about 3 foot high and about 30mm or more in diamter. They then have a whip type antenna on top of that, making them anything up to 8 feet tall.
Cheers,
Roachie

Footloose posted:

Bob, although rear mounting does afford some protection it also has disadvantages. It's easy to forget you have it on if parking under something, especially servos. One guy I know took out a lotta floros at a fuel stop. Since you can't see the whip of an autotune mounted on the rear, if it gets whacked by a tree branch or falls off on corros then you might not realize it until you need it.
Dammed if you do and dammed if you don't I rekkon :))

Bob of KAOS posted:

Thats true. I have scraped the roof of the roadhouse - no damage luckily.

Tuco posted:

I have used HF taped whips and also Barrett autotune units both on the bullbar and also on a rear wheel carrier mount and have found that the rear mount is better for a number of reasons.

1. Visibility is not restricted at all with a rear mount autotune.

2. Interference from alternator whine, electronic fuel injection (petrol or diesel), spark plugs, plug caps and leads (petrol) when using the HF in a mobile situation is much reduced in a rear aerial setup. Many people only ever use their HF when stationary without the engine running - so no difference. On some vehicles that we have owned, we were not able to use the bullbar mounted aerial when mobile - simply because of the noise interference. By moving the aerial to the rear of the vehicle mobile communications were possible.

3. Toyota and also some other vehicle manufacturers warn of the possible damage that high powered HF transmitters may do to the electronic engine management sysyem on modern vehicles. By locating the aerial at the opposite end of the vehicle and away from the ECU - then the risk is minimised.

The radiation pattern of either bullbar or rear mount is very poor. The centre of the roof will definitely provide the best omnidirectional pattern. BUT how many of us could accomodate a long whip on top of our vehicles - not practicle.

Footloose posted:

You are correct up to a point. See http://groups.yahoo.com/group/codan_outback_radio/files/Auto%20Tune/
to dispel some common home "truths" on front vs rear mounting.

Tuco posted:

Hi Footloose - that is a very interesting test that Codan have done with regard to the radiation pattern. Clearly shows that it isn't linear either with some bands improving by as much as 2dB while some are 9dB down.

Most of my galah sessions are on 5145 or 6950 and so far haven't had readability complaints.

My bottom line is that with the rear mount I can use the HF mobile, but with a bullbar mounted aerial - too much electrical interference noise.

Cheers - thanks for the link.