Fitting a CB Radio for off roading

CB Radio Installation

A CB is quite an important part of any 4x4's kit mainly because it allows you to talk, or laugh at your fellow off roaders when your out playing with your vehicle, something you cannot do using a mobile phone.
Now its been a long time since I've had a CB, I think the last time I used one in the UK before fitting on to Larry was in the early 80's oh yes!  The early 80's!

Anyway, without going too much into my past, my asymmetric wedge, Russian shirts and pixie boots and a passion for Ford Escort MKII's we should move on with the times, quickly would be my preference.

Oddly, back in the 80's you used to pay for a CB license and also was restricted to 40 channels FM at 4 watts output.  To my surprise when I was looking at CB's for Larry, I found out a license was no longer needed and also you can now buy multichannel CB's legally, there's even a rumour that SSB will be legalised soon in 2013 without the need for a Radio Ham license, gosh!

Anyway, after some shopping around I bought a Intek M799 Multiband CB with 80UK channel FM/AM and its also legal across most of Europe and beyond.

Intek M799 stock photo

One thing about the Intek, its really small and could be fitted in a discreet place in your car.

I also bought a gutter mount and 5/8th antenna.  Now, the only thing I will say is don't get a gutter mount for a Discovery 1 is they don't work.  If you try to fit it, the aerial will be at 30 degrees to the gutter and will poke out sideways from your Landy, this is not good.

So after a quick trip to Maplin I bought a large magnetic mount antenna base for £15.  I had also ordered a SWR meter, so all the CB kit was about £100, I could have spent £60 but I wanted a European CB, so ner.

Now some technical stuff about SWR, ground planes and where to mount your aerial.

Mounting a CB radio to talk to someone about a mile away when off road is not really an issue, you can plonk it pretty much anywhere you like on your car.

However, if you are a Defender owner you need to know that although conductive, aluminium does not make a good ground plane, steel on the other hand does, not really a good reason to buy a Discovery over a Defender, but good in my books.  If you are a Defender owner reading this a) you will not be using a mag mount and b) the aerial will probably be at the front or rear of your car, or on a light bar or bumper.

Anyway, to maximise the general coverage of the CB radio on your Discovery you should put it bang in the middle of the roof, that way the signal you will transmit and receive will broadly be even around the car, or omnidirectional.

If you put the aerial at the front or back you will amplify the signal opposite to the aerial mount, making it directional. This is pretty cool if you want to use you car as a directional ground plane and gain extra sensitivity in front of you, but will limit the range of the radio behind your car and to the sides.

I have explained ground planes in the very complex computer generated diagrams below.

Aerial in the middle of the car

Aerial at the back of the car

Image Legend

Green = Car

Blue = Signal

Image Legend if you are colour blind 

Square = Car

Roundy ish Shapes = Signal.

SWR, or Standing Wave Ratio

An SWR meter is a piece of kit that measures the amount of energy reflected back to the CB when you are transmitting, normally caused by a badly tuned aerial or a lack of ground plane.  The idea is to get an SWR measurement as close to 1:1 as possible 1:3 being usable but loosing effectiveness of the radio with the possibility of causing it some damage.  My aerial came pre-tuned, and would you believe it, it was very close to 1:1 so it was good to go out of the box.

If however you get a CB and check the SWR and it generally higher than 1:2 on the meter you need to tune the aerial by making it shorter or longer, this is normally done on car aerials with an allen key and sliding the whip of the aerial into, or out of the base.

Remote Controlled Land Rover

Anyway, enough of the expensive graphics and technical stuff.  I shoved my aerial in the middle of the roof and it worked well, see below.

Now my girlfriend who shall be nameless, but for future reference we can call her Rachel, said Larry looked like a remote controlled car with the aerial on him.  Idiot controlled car I could live with, not remote controlled, that seems to imply there's some spotty kid driving Larry from afar.  Whereas it normally me being the idiot in it.

Rachel did have a point however, I had picked a large one for Larry, which did work, got good range, and fell off when whacked with tree branches.  So I said to Rachel (during our first trip out in the woods) I would get a shorter whip soon, this would stop all the banging at the side of the car when we were out together.  No sniggering, it's not that kinda whip I'm talking about, or that type of banging, I'm talking about the large metal rod sticking erect out of the top of Larry.

Fitting the CB

Anyway, fitting a CB is dead easy.

I did not want to leave the aerial on Larry when not in use, so I put the aerial in the middle of the roof (clump it goes), run the cable several times around the roof bar and then into the rear door and into the back of the radio.

Wire wrapped around roof bar

It's just as well I did run it around the roof bar because at least when the trees knocked it off it dangles down and does not go under the wheels, which happened twice in one trip.

The CB itself is fitted into a CB bracket and the mike on a mike bracket both held on by two screws.  All I needed to do was drill into the plastic inside the car and put the self tapping screws in to hold the brackets.

CB Bracket

Mike Bracket

By taking this approach I can put the aerial back in the car or in doors with the CB itself when not in use, pictures below.

All in all a simple mod for a Discovery 1, and well worth it when out with other Land Rovers, or indeed lesser brands of 4x4.

CB Installed

CD on powered from the cigarette lighter

CB Performance

We have used the CB now a couple of times, it has worked very well and the range on flat ground has been anything upto 8 miles which I'm amazed at.  Obviously when off roading in hilly areas the range is a lot less.

The 7" mag mount has had no issues holding the aerial on down the motorways even with the big whip it has and all in all it works!