And they say there's no such thing as a stupid question! UHF's...

Scoey, when you are travelling in places like the desert over sand hills it is always wise to know there isn't another group over your sand dune who is travelling in the opposite direction. Some scan as they go listening, but also need to be tuned to the convoy channel to be able to transmit.

Aside from that it is wise to carry a spare antenna and if you have been scanning, you will also have a spare radio. When we crossed the Simpson two years back Moses UHF antenna failed and I have heard of others having similar problems.

Some radios can scan but still have the priority channel to transmit to but it is still wise to have that spare antenna.

G'day

Yes you can run 2 UHF antenna's. Heavey vehicles do it all the time (one on each mirror) to give good coverage around the large vehicle. Same antenna type is used on both sides.

What you might see on a 4x4 is a high gain GSM/CDMA mobile phone antenna (usually a black or white fibre glass antenna) and a UHF antenna (can be a white fibre glass antenna) similiar in look to the mobile phone mounted on either side of the bull bar.

Regards

Paul

Scoey.

I should think you could run the two different aerials through a switch (would need to be made for the task) and just switch from low to high gain. The only problem I can see is the additional loses through the switch. You may lose more than you gain.
excuse the pun.

I run two radios for the reasons John mentioned.

Regards

Thanks for the responses everyone! It was interesting to think about anyway!

Cheers
Scoey!

Scoey,
why not contact the experts in this field rather than get lay opinion...Call a supplier of such communications equipment and they will give you an "expert answer".

As an example when I first fitted my UHF a bloke told me he obtained this amazing feat of UHF communication over vast distances based on this enormous surf rod size fibreglass antenna. So I thought I'd follow his lead.

So I visited the supplier and fitter of my unit. Now you'd think a retailer would be more than willing to relieve me of my money and supply a similar antenna I may not need. To my surprise they actually explained all the theory of UHF communications and why such a setup was of little advantage to what I already had.

The moral is always speak to an expert in that field.

John, using an antenna on each side of a large vehicle such as a truck helps the signal get around the vehicle to the back and sides. Also the pattern can be made very directional by a ¼ or ½ wave phasing harness. Hams don't seem to bother with dual antennas when mobile so I can't see a great deal of advantage, we are usually interested in good all round mobile coverage.

I have a UHF and an older 27mhz CB. Both have a laser s/steel whip aerial of about the same length, one each side fo the car. That car could have been the same.
Also have a s/steel whip aerial for the FM/AM radio. Got fed up branches taking out the extending aerial that came with the car. So that's three :-).

So to summarise
- you can't connect two aerials to one CB (unless you have a special phasing harness).
- you can switch two aerials to one CB using a Coax switch rated for UHF.
- there are lots of aerials for other radios/phones that look like CB antennas.

Mike

Woop from GQ forum runs several radios in his GQ.. VHF, UHFx2, AM, HF, and a few other NFI freq's.

Scoey. Yes, you can run two UHF antennas off the one radio.
No, you really can't get the best of both worlds by having a high gain & low gain antenna - unless it is possible & practical to have each antenna well outside the capture area of the other antenna.
An impedance matching phasing harness will be required to couple the two antennas to the one feedline (coax cable).
Is it worthwhile doing it? Probably not!
Repeater sites often used multiple folded dipole antennas to obtain both gain and directivity.

Some more technical stuff that may be of interest.

Using multiple antennas is called stacking. It is normally done to either have maximum gain or to have a very narrow capture area. It is used on repeater sites (above) and also for very high gain directoinal yagi arrays.
Stacking uses identical antennas connected via phasing harnesses. Connecting cables in the phasing harness must be of identical impedance and of the same length.
Stacking can be done vertically and horrizontally or a combination of both.
You will get nearly 3dB gain (double EIRP out or received signal in).
Gain measured in decibels is logarithmic in nature, the laws of diminishing return applies.
Example. 2 stacked antennas gives nearly 3dB gain over a single antenna.
4 stacked antennas will give nearly 6dB gain over a single antenna.
8 stacked antennas will give nearly 9dB gain over a single antenna

If you want to see some really serious stackes arrays go to RN6BN www.73.ru/ a href="http://www.73.ru/">RN6BN

Cheers, Tony