UHF <span class="highlight">antenna</span> - wire or fibreglass?

Probably not quite that simple Mike.

Your looking to go up 1.6db when as per another recent radio post i made radios can have up to 4 to 6 db difference in gain (not including those with non legal 25w output).

It quite possible that you can get that gain by taking trouble to put in fatter better cable.

You may know that your antenna has to be keep pretty straight to achieve its 8db gain and then will only give that gain when it is not obstructed , this means base of antenna needs to be above the level of the windows , particularly if windows have the film tint on them.

Many people then have roof racks which obstruct them further.

Even when achieved the antenna becomes directional.

One thing I suggest to anyone with some of these issues is to get a cheap 1/2 wave antenna from Jaycar etc which comes complete with cable and attach it up high (maybe on side of roof rack if have one - but not connected with metalbracket for first 6 inches).

Use this aerial as a reference , its often better than 2m bullbar mounting ones and also suffers from less directionability, and will not break as easily.

How much range do you want?...... antenna dB gain if great for adding distance if both parties are a constant.

There are too many variables involved as it relies on how well each radio transmits and receives.

Going up 1.6dB may in fact give you bugger all difference and may not be worth the extra time, money and hassle...... if you had a 4dB antenna and you went up to a 9dB you may see a noticeable difference under some circumstances.

There is way way to much emphases put on antenna dB gain in most mobile UHF CB situations that involves other parties you have no control over.

As for antenna choice..... it's personal preference driven by cost, looks and function.

Something to remember about the propagation of a vertical radio signal. And I will use an analogy so that it can easily be understood. Now grab a stick in the middle and hold it straight up and down. ie vertical. Now walk along with one end touching the ground. Just imagine that after a while it will eventually wear out and fall over

Total signal loss. Sure a stronger or higher wattage would mean that it would go further but you really have to make it thick or much greater power and just going from 5 to 25 watts is not a big jump.

So to improved the "reach" we clean up the signal before it even leaves the car. Firstly get it mounted higher. On the roof is best but watch for carports, garages and underground car parks.

Then just as Robin said, get some better quality cable. Make sure there aren't any kinks in it. Kinks or sharp bends will knock it back very quickly. Now make sure all terminations are done properly. No dirty or dry joints etc. If crimped then don't use the bench vice to crimp it.

Then get a VSWR meter and check it.

Personally for UHF I suggest that unless you are competent with high reliability soldering and clean work space practices, I would pay to get done and tested with a VSWR meter.

The installation in the car is where more problems exist and where errors are made. The VSWR test is a good guide.

Now if you want more then go and put a big stick on the car but I think you should be happy with the improvements done by cleaning up your installation.

Side story:
I run a 9.6 db , 5 element yagi on a 50 foot high tower for hf bands. It's called a Wilson System one. Not the biggest hams station in the world by a long shot. But I had a spotless installation, technically that is. No connectors crimped with pliers nor any soldering done with a gas flame etc. But the best thing that I ever did was use extremely low loss cable that I purchased after a "special" Defence site was demolished. With that set up I reached Burbank California on 0.75 watts on 28 Mhz. A record. The others around me weren't heard at that power and only one local station could hear the California station. I have also been told that I had the biggest signal out of Australia during contests. And without any power amp and just running 100 watts I have won several international contests.

Most of this success with my home station and providing base comms for Australia wide car rallys etc, I attribute to my meticulous technical aspects of the installation. I did it professionally back in those days before computers. Sure I am blowing my own trumpet but I have the trophies and awards to prove it. Australian HF Champion several years.

I had a "clean house". Just as we are recommending that you do. The try a larger antenna if you really wish.

Phil

Distance required is up to 60km across the plains to a base station when camping out. A directional antenna for temporary setup could be an option. Unfortunately there is no repeater around.

Hi Cybermike,
I can not comment on the merits of db ratings of UHF antennas.
I can comment on steel or fiberglass.
I have had steel antennas before and each one has snapped off due to no flex, especially if travelling along corrugated roads.
I have a RFI fiber glass one now and it wobbles around a lot but stays intact.
Hope that helps.
William

C'mike,

Re thread query, think all aerials use a 5/16" thread, unless they're the ones that screw onto a SO-239 base.

Bob.

Fibreglass has no effect on the performance of an antenna. A fibreglass antenna is simply using the material to support the active antenna element, the wire. An antenna that uses a ground plane will normally give better performance in any given situation. High mount, free from closely placed vertical interference elements, will give best performance for a given antenna.

Iza

There's a lot of info here - thanks to all. Yes - it is while working out at a large outback property. To get a yagi with enough increase in dB would be a lot to lug around & I already have too much gear to pack! It sounds like the go is to have a 1/2 wave antenna hoisted over a tree branch. I'm onto a supply of Heliax L4A cable which I'll get a radio technician to solder. I'll also get the mobile 6.6 dB antenna reconnected with this, & remounted from the bullbar to the roof. Cheers, Mike.