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4 X 4 CB
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UK CB Radio Specialists - Expert Advice, Competitive Prices & knowledgeable staff, Est 1996

Installing CB Into 4x4's   Tuning the Aerial
Before You Start   |    Connecting to Power   |    Finishing Up   |    Fitting the Aerial & Mount   |    General Installing advice   |    Installing the CB itself   |   

This is the most important part of installing a CB, and it's the bit that can have the most effect on how well your CB system works...

Don't listen to anyone who claims to sell aerials that don't need tuning in (SWR'ing) - there's just too many factors in the installation that can affect an aerials tuning for this to be true.

The most important of these being the aerials earth/ground - absence of a sufficient earth means a VERY high SWR - no matter what the claims of "pre-tuned" aerials say!

You need to use an SWR meter, an inexpensive and simple to use piece of kit - but please make sure you are familiar with how to use it... Click here to view our SWR meter users guide

The aerials we sell are the right length, this means that as long as your earth is good, and the actual aerial (in particular the coil) is not too close to any metal around it, you should get a reasonable SWR straight away.

You may need to adjust or cut the whip for the lowest reading.

If you do need to adjust the aerial, there is usually a grub screw to loosen at the top of the coil, to allow you to move the whip in and out . Where this is the case, you are acting on the wire "coiled" up inside the coil, so moving the whip in or out by half an inch may actually alter the length by several inches, so small adjustments are needed. It's often easiest to cut the whip as you will normally need to make it shorter if anything.

Most aerials will tune in fairly well across 80 channels, but in order to get a very low SWR across all 80 you will need an aerial with a wide bandwidth - most of the Sirio range would be suitable. Aerials with wide bandwidths are usually very good performers although often more expensive than the more basic aerials.

You will probably find that most CB activity in this country, both off-road users and general users, will be on the UK band, so if you have problems SWR tuning over all 80 channels, try to get the best reading you can on the UK band.

This should ensure that at least the top channels of the EU band don't have too high a reading. You may have to do this with small (3' and under) aerials.

You may find that in some circumstances, often with aerials made in Europe, you will need to cut the whip. Do this with some caution. If possible try to find another piece of rigid wire that's the same length as the whip of the aerial (fencing wire is ideal but a straightened coat-hanger or similar will often do the trick).

Use this as the whip and cut it down to size until you find the right length to give you a good reading, then cut the actual aerial down to this size and re-fit. This will prevent you cutting too much off the aerial by mistake, and the wire will probably be a lot easier to cut than the aerial's steel whip, saving you time.

You may need to take anything from 1-5 inches off some aerials to obtain a very low SWR on the UK band.

Aerials made in Europe are tuned for the EU band and below, and we want to tune them for the EU band and above, hence why you often need to cut them. Luckily it's this way around, as it's much easier to cut a whip down than it is to add anything to it!

Usually there is a grubscrew to undo so you can move the whip in and out of the coil - these usually come fully "home", so if you cut too much off, you can raise the whip a bit to compensate for it.

Making sure the aerial is correctly tuned is very important, as the power that does not get transmitted due to a bad SWR comes back down into your rig and can cause damage. Not only will this eventually lead to the death of your rig, but the performance of it while it does still work will be very much worse than if the SWR was good.

Although all new CB sets that we supply have a 12 month guarantee, this does not cover the output transistors, as they can be damaged by using an incorrectly tuned aerial. On older CB sets that have been around for years it is quite possible that the components are no longer available and if the set fails due to bad-SWR damage, the unit will be un-repairable.

If your SWR is very high, it's likely that your earth connection (groundplane) is not good - we have more information about groundplanes and curing earthing problems here. Following the advice in this section should mean that you have no problems installing and tuning a CB set-up.



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