How to choose a uhf antennae?

Hello Jude,

Forget about the aerial for a moment please .

I think you might jave made a mistake with the radio . Why did you buy a 27 Meg radio . Most people on the tracks you pass will be using UHF .

Is there any way you can change it ?

Willie

Sorry fpr any spelling mistakes - I cannot read this as I have lost my glasses .

Hi Jude
The only people that use the old 27MHz radios these days are truckies. If possible, get a UHF and you will be able to keep in contact with nearly all vehicles that you see up in the Cape.

Cheers

Stephen

Jude,

Willie is quite right.
27MHz CB has been superceded by the 40 channel UHF CB which everone else is using.

You will be extremely lucky to communicate with anybody on the old CB and therefore it is all but useless to you. I recommend you do not spend any more money trying to complete the installation.

Bill.

And when you do get your UHF, suggest that you check each day that the tip is screwed down tight to the aerial base (they loosen up and drop off, especialy on corrugations) and carry a spare small, cheap tip in the glovebox (the usuals knock off better tips around towns).

Thanks everyone for your help. Once we have the uhf, how do I go about choosing an aerial or antennae?
Thanks,
Jude

Recommend using a UHF CB - the old 27MHz ones are long gone and not much good anymore.

Nearly all the property owners use UHF and there are a large number of UHF repeaters available for emergency use should the need arise.

There has been a lot said for the best antenna. After commercial testing I would only fit the RFI model CD63. Below is the info on this antenna.

http://www.rfi.com.au/downloads/wireless/mobile-antennas/citizen-band/477MHz/CD63.pdf

A lot of people say 'but this one has more gain'. Dont listen to them because the more gain with an end fed antenna the greater the down tilt and narrower the beam width. So you have a pencil beam pointing to the ground. Not much good unless you are on a 3,000m mountain and looking to talk to someone on the bottom of the hill. In any case UHF is what they call 'line of sight' and it is impossible to tell the difference with a signal with 3dB more of less antenna gain between two cars that are moving. Better to have an antenna that puts the power where you need it, in the direction of the person you want to talk to, not into the ground.

Remember the more phasing coils in the antenna the more down tilt. Dont buy an antenna that has more than one in the middle. The lump on the base is the loading or matching assembly and it's better to have a 'ground independent' antenna as these do not require a ground plane unless you intend mounting it in the middle of the roof.

Testing has shown that the CD63 out performs just about every other UHF CB mobile antenna. We tested them on cars, trucks and motor bikes. The CD63 is cheaper and less likely to break due to its construction and weight. Sorry people but the CD63 outperformed the very popular elevated feed monopole (that silver long bit on the bottom with a longer bit on the top).

The other myth is dB or dBi. The easiest way to remember is to use a rule of thumb 0dB = 3 dBi (it's actually a bit less than 3).

The 'i' is for isotropic or a point source. Think of the light from a bulb without a reflector whereas dB normally refers to gain over a folded dipole or similar to a donut. The more gain the narrower the beam width. Shine a torch on the wall, then change the focus to a smaller area, note the light intensity is greater but the area is smaller. This is what happens when you increase the gain of an antenna, you put the energy into a smaller area.

The other effect is to do with the number of phasing or delay lines in the antenna. These are the coils in the antenna which are used to phase more elements or increase the gain of the antenna. As said above each time you introduce a delay in the antenna you cause more down tilt with an end fed antenna. So the torch is tipped down and you get less light onto the horizon were you want to achieve more distance.

The salesman should have asked what the CB was going to be used for before he sold the unit to Tone and Jude .

Just wanted to thank everyone who gave us advise on th CB/UHF ordeal. Tone read your messages this morning and rang GME who confirmed what you all had said. Thankfully we can return the CB and a new GME UHF/Aerial combo pack is arriving tomorrow from wonderful company in Adelaide (am I allowed to name?) offering us free next day shipping!
So, disaster-causing-divorce has been averted and the holiday will go ahead, thanks to you all.

Cheers,
Jude