Aerials of Bullbars - are they legal?

What was exactly said by the inspector? There my be some contributory factor to the installation that was the reason for the knock-back and your friend took it to mean all antennas. As well as the 30 mm maximum diameter there are things like sharp edges around or in front of the bar that would be the reason for the failure knock-back.

I was really doubting what he said but my mate was pretty clear that they had to remove the aerial before they could get a roadworthy.

Sorry but I can't answer your questions as I don't have the facts. I'll get in touch with my mate and see what he says. I've asked for a photo from him so I'll await his reply and get back to you all.

Thanks for your interest.

WBS

G'day Boobook,

I have a spring based antenna for my UHF on the 'roo bar of my vehicle. It's been there for many a long year and is mounted dead central. I have travelled to every state and never had anyone (copper) tell me to remove it. Must be a VIc thing, lol.
I have heard it's not the best place reception and transmission wise. The center of the vehicle (roof?) is AFAIK the best spot. Unfortunately IMO it is also the best spot to get it wiped off in some off road situations. My memory being what it is and "out of site out of mind" being in play I would probably blissfully drive under an over hanging branch and then wonder why my UHF wasn't working too well.

To your knowledge, are there any better design antenna or mounting spots, maybe on the rear of the vehicle??

Cheers
Pop

because most of the decent UHF aerial designs are ground plane independent, mounting in the centre of the roof makes very little difference.

Being High and clear, on the other hand makes a great deal of difference in UHF.

Mounting an aerial of lighter construction on the side of the roof rack on a simple knock down mount is definitely the way to go.

The best bang for bucks is the 6db, elevated feed areials that pretty much every aerial manufacturer makes ..... they have as good if not better gain and radiation pattern than most of the big white sticks, people spend a lot of money on and mount on their bullbar.

A simple and effective knock down mount can be made out of a couple of short pieces of angle a but, bolt and a fibre washer.

Another option is the 4.5db rubber ducky .... several manufacturers offer these ..... they are very popular in the earthmoving business ..... they are near impossible to distroy ..... and if mounted high and clear, they will perform better than an expensive big white stick mounted on the bullbar.

cheers

Yep, Wot he Sayz ^^^

Totally agree with the Bantam. Height is might.

I made a knock down bracket out of 50 x 50 x 6mm right angle aluminium, 50mm long. I bolt the antenna to that, and bold it to the rails on the roof which go front to rear. As Bantam says, a lightish elevated feed antenna does the job. If I hit an overhead tree or car park, it just folds down. No need for the center of the roof. Just as high as possible.

I can tell you that a 6db on the roof will definitely outperform a massive 9db broomstick every day of the week. My 2 reference points are
-Previously I had a 6.5db elevated feed on the bullbar. It would ony ocassionally "hit a repeater" about 30 km from home. When I moved the antenna to the roof, even a little 2.5db rubber ducky antenna worked reliably every time.

-On a desert trip I was talking to another convey many km away. All the other guys in my group had antennas on their bullbar. One even had one of those stupid massive broomsticks. All asked who I was talking to. They could not hear the other end's part of the conversation at all.

Chalk and cheese.

Thanks Bantam and Boobook,

The antenna I presently have, a Terlin brand, and bought at a 4WD show a couple of decades ago is 1600 mm long. Handy to hang a sand flag off for dune work as the mount is 1400 mm off the ground so about 3 mtrs to the tip.

I always have to take it off when around towns and especially underground car parks.

Cheers
Pop

I have a massive broomstick because my GME wire antenna broke halfway along the Oodnadatta Tk on it's first outing from Victoria.
As far as db rating goes I always understood that for hilly terrain you need a lower db rating & for flat desert type country a higher rating is better.

Shaker, what you say about db verses flat desert is fundamentally true, though keep in mind 4 things.

-Like for like location, higher gain will 'focus" the beam horizontally. and give you better performance. However the effect is not as simple as the marketing stories and pics. A 4.5 - 6 db antenna will almost always perform better than a 3db. - even in hilly environments. And if you are in mountain terrain remember it is still line of sight anyway. Also if you are driving up a hill, then other cars will be up or down that hill, in line with the focussed 6db gain antenna's radiation pattern. Similar to if you walked up a hill at night, you would point the torch up the hill as you walked. Same same.

-Being line of sight, the transmissions go to the ( radio) horizon. The higher the antenna, the further the horizon. Same physics as lighthouses. And you never see a lighthouse mounted on a bullbar ( or half way up a cliff) :-) . The range from roof to roof is about 3- 4 km more than bullbar to bullbar even ignoring the next point.

-A bullbar mounted antenna has to penetrate through the windscreen, you, cargo barriers, window tinting etc. Generally the bottom half of a broomstick antenna, and most of a normal height antenna is not doing much, particularly to the rear.

-Vibrations on the bullbar are greater than on they are on the body of a 4wd, damaging the antenna. You may not even know that your antenna's performance is reduced until it is a catestprohic failure.

In other words, a Broomstick antenna on a bullbar will perform better than a smaller antenna which is also mounted on the bullbar, however your 8 - 9 db bullbar mounted broomstick won't perform anywhere near as well as a 6db rooftop antenna. The one thing it will improve however is the manufacturers profit, and it looks 'tough' to some who assume they are better.

If you ever see an antenna mounted like this, then that is even worse.


Take a look at my signature pic. That's where mine was many years ago before I looked into it. My SWR was about 3 for those who are into that stuff. I later moved it to the top of the bar then to the roof.

I thought the higher the db rating the flatter the signal is transmitted.
My "broomstick" aerial is 6db, which is a compromise.

Have a read HERE

Sure Shaker, that is what I was getting at. Apologies if that wasn't clear.

This whole gain for terain thing is grossely over simplified marketing BULL@#$%.

It simply does not work that way in theory or in practice.

The pictures shown in the marketing diagrams are massively exagerated, and nothing like the published plots for any antenna.

AND vertical dispersion patterns are not directly related to gain, different types of antenna mounted different ways will produce different vertical dispersion.
Some high gian antennas will show some vertical compression in the radiation pattern other of the same gain will show practically none.

This much talked about vertical compression is almost insignificant until you get into 9 and 12db aerials and even then it is nowhere near as narrow as that pictured in the marketing hype ...... most 6db antennas are near omni-directional in all planes when mounted in free space.

Further, a vertically compressed radiation pattern is an advantage in every case, because UHF radio does not use skywave and if your vehicle is tilted as much as in the published diagrames you have more on your mind than radio reception.

In pretty much every case, more gain and more height will win .... by a long way.

As far as wire antennas breaking ....... yeh it is common for wire antennas to break from fatigue when mounted on the bullbar ...... though I know of 6db elivated feed antennas that have been on bullbars for over 20 years doing hard work with no issue.

The wire mast sections are cheap enough and easily replaced OR you can buy exactly the same aerial with a fiberglass whip that is electrically identical.

Bullbars are THE worst place to mount an aerial, one reason is that it is THE worst for vibration .... it is at the extreeme end of the chassis and near enough to be rigidly mounted to it ....... mount on the body toward the centre of the wheelbase and vibration is massively reduced.

To summarise ...... gain for terain is utter rubbish ........ more gain and more height wins nearly every time.... and by lots.

cheers

I think you will find it about damage it can cause if you struck a pedestrian.
I know the fishing rod holders for example here in WA are illegal if mounted on the front of your vehicle.

If this is your copper mates photo, I'd say he has made an enemy......as that aerial would comply with any state standard..

Having relatives in the police means nothing.

In practice most inspectors in most states would allow the aerial pictured.

But by the letter of the ADRs it is clearly not compliant, because there IS another option and it does represent an non-compliant protrusion.

If the spring was below the line of the bullbar it may be viewed differently.

If a child got its skull ripped open on that excessively large spring ...... don't be surprised if you get sucessfully sued, by either the parents or their insurance company

cheers

Pfft....nit pickers....

Take it somewhere else....

The question is "legality" and that is all about nit picking .....

indeed correct, this is why I have a plain flat fairlead and take the winch hook off when not in use.

cheers

This is also why some ... a very few .... bullbars the winch rollers are recessed or guarded.

cheers