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Mobile Installation:
Some Do's Don'ts & Advice.
By Brian MW0GKX.

This advice is not vehicle specific, I mention the fitment to my Toyota Yaris as an example.
I have had over 20 years experience as an auto electrician, dealing with Mobile Phone, CB, I.C.E. and Amateur Radio installs as well as general auto electrical work. In this time I have picked up quite a "knowledge base", some of it is just common sense that could be forgotten in the "heat of the moment". I hope some of it will be useful to your install.

General notes for mobile transceiver fitting.

With the proliferation of all the on-board electronics in today's vehicles, especially microprocessor based electronics, the proper installation of the mobile radio has become more important than ever. Interference issues are bi-directional, that is, the radio can interfere with on board electronic systems or the on board electronic systems can interfere with the radio. Either type of interference is undesirable, but when the radio interferes with the vehicle electronics, the results can be anything from comical to disastrous.

Interference to a vehicle's electronics system most often is caused by the mobile radio when transmitting. However, interference can result when the radio is receiving. Any signal that is radiated or conducted away from the radio is a possible cause of interference to any on-board electronics. This type of problem should be eliminated in the radio design stage through proper internal shielding and decoupling of input/output wiring.

Most mobile radio manufacturers provide information on how to check out any possible interference with the antilock braking system. Follow these instructions carefully and fully to ensure that no EMC problems exist. Check for other EMC problems during a test drive, ensure that the test drive is at a quiet time of day on an empty road. Check for proper receiver operation and for any interference to the vehicle operation while transmitting. If the radio has variable power output start at the lowest power setting and work up.

If you experience any problems with the test Stop Transmitting Immediately and assertain how to remedy the problem. Check all operating frequencies.

Some of the vehicle manufacturers actually care about mobile radio installations and offer guidelines to optimise radio performance and minimise interference with on-board computer systems so it could well be worth a call to the dealer or a look at the manufacturers website.

First considerations:

Choosing the right radio:

If you are thinking of using an Amateur Radio mobile and are going to get another radio for mobile use but not purchased it yet there are some things you should consider first:

Once these all things have been taken into consideration and the radio has been purchased, then the fun can start!

Fitting: Transceiver:

Power Supply:

To reduce the hazard of working on the vehicle, disconnect the battery NEGATIVE before beginning work. Note that some components may lose short-term memory (e.g.: radio presets) after a time without battery power.

Important WarningIf air bag(s) are fitted and you will be working in the area of an air bag wait at least 5 minutes after disconnecting the battery before continuing. (Have a cuppa and take time to think through the rest of the install).

Physical Mounting:

Try the installation out before you start drilling holes. When you have decided where the various components are going to go you will be drilling holes to secure things (unsecured anything becomes a missile in an accident). Check the other side of where you are going to drill / screw whatever. I have seen fuel and brake lines severely damaged due to not checking, a flat floor inside is not necessarily clear underneath (I once drilled through the floor of a van, knowing that there was no wiring, fuel or brake lines in that area. Unfortunately I forgot the spare wheel! A new tyre 'cured' the hole in the sidewall! an expensive hole).

Similarly a clear space on the dashboard could have cables or even an airbag the other side!

Fitting: Antenna:

Obviously, the choice of antenna placement or location on the vehicle is critical. Antenna location must be considered from both the standpoint of interference to and from vehicle electronics and performance as an antenna.

Several factors have to be considered in choosing the location for the antenna. These factors include your preference, the best operating location from the receive/transmit perspective, and the best location to minimise any possible electromagnetic compatibility (EMC) problems with the vehicle. It may not be possible to totally eliminate all EMC problems within a given vehicle but you should ensure that, at least, your transmissions do not affect the vehicles normal operation. The use of a magmount antenna can be helpful in checking out various antenna mounting locations for possible EMC problems.

Routing Coax:

Physical Mounting:

Permanently installed antennas are preferable over magnetic, glass or body-lip mounts for anything other than for low power or temporary installations.


I'm only covering basic interference issues here as whole books can, and have, been written on the subject. Obviously some sources of interference only occur on odd occasions, for example my electric mirrors give horrendous crackle but, being used infrequently, I put up with it as it is quite a job to suppress the 4 motors inside the mirror casings.

One Final, but important, Tip:

If you haven't already, and you do fit a transceiver, fit an alarm! any local "scroats" will gladly remove the rig for you without being as careful as you were when fitting it! (and in a lot less time, too!).

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