CB Radio Guide - What is a groundplane?

CB Radio Guide

Groundplane Introduction

Groundplanes can cause trouble even with the best CB setup, if your Groundplane isn't very good then your antenna will not perform as well as it should.

A Groundplane is needed for any CB antenna to work, without it the antenna will not transmit very well and your SWR reading will probably be very high.

What is a Groundplane?

Simply speaking a groundplane is the metal-work underneath your antenna, for example if you have your antenna mounted in the roof of your vehicle then the roof becomes the groundplane.

"In effect a mobile CB antenna is only half the equipment needed to transmit a signal, without a sufficient groundplane an antenna will not work very well at all."

What makes a good Groundplane?

Generally speaking anything that is a good conductor will make a good groundplane, so metal such as aluminium, steel or copper will work fine.

Therefore most vehicles will be fine if the antenna is mounted in the roof, however if you have a vehicle that doesn't have a metal body or roof, such as a lorry or tractor with a fibreglass body you may need to introduce a groundplane yourself.

How do I know if my Groundplane is sufficient?

Normally if your groundplane is not sufficient you will know, as you will struggle to get a low SWR reading when tuning your antenna. So if you have followed our SWR guide (click here) and are not able to bring the SWR down to an acceptable level (below 2.5) then you will probably have an insufficient groundplane for your antenna.

How do I improve my Groundplane?

If you believe your high SWR reading is caused by a poor gorundplane, or if have a fibreglass roof you can do one of three things to improve it, the first is the easiest and cheapest;

1) Run a wire from the antenna mount to the chassis of the vehicle. The wire needs to be as thick as is possible, anything over 10amp rated is suitable. Make sure it is attached to the ground part of the mount. This normally works in most situations, however if it doesn't you may need to look at the next suggestion.

2) If you are mounting the antenna on a mirror arm, or on a bar with enough space underneath, use a 'Ground Plane Kit.' These are antenna mounts with metal rods underneath to provide a groundplane for the antenna, click here. If this type of mount is not suitable, (i.e. you are mounting the antenna on a roof) then you will need to look at option 3.

3) Attach a metal sheet or plate underneath the mount, if the antenna is mounted in the roof then a metal plate underneath the mount is best. You can use aluminium, steel or copper for this. The bigger the plate, the better, make sure it is at least 1 foot square. You will probably find that running a wire from the plate to the chassis will also help.

If you need any more advice on ground-planes or anything else regarding CB antennas, contact us here.