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.
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.
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:
It may seem obvious but if you don't want to work HF mobile then do you really need something like an FT-857 or IC-706?
When you are on the move you don't want to be fiddling with menus etc., buttons that are too close together and small could mean the wrong one gets pressed, especially on todays potholed roads!
If you have a small area to fit the radio in the dash a 'remote head' would be a better idea than trying to fit in the complete radio, a remote kit may be an additional cost to be borne in mind when budgeting or, as in my case, a dig through the "junk box" and a short while with the soldering iron fashioned the lead lengths required.
The fitted position for the controls should be easy to see, not obstruct the vehicle controls or distract the driver (even if the driver is the operator). See also: Legal standpoint.
Don't Do It! Do not mount any transceiver, microphones, speakers, or any other item in the deployment path of an airbag, it will become an instant missile should the airbag inflate. Even more difficult these days, my Yaris has 9 airbags!
Wherever the radio, control head or main unit is going to be positioned there must be adequate ventilation or the equipment may overheat.
In my Yaris I had a dual "map reading" light above the rear view mirror which, when removed, left enough room for the head unit of my Icom IC-2800 to fit snugly. Visible to driver and all passengers, with the controls within easy reach from either front seat. The control cable runs inside the roof lining and down the windscreen pillar behind the plastic trim.
If using the remote head then consideration should include where the main unit is going to fit as well as the controls. Under the passenger seat is a common mounting place for a main unit, but check before you decide to fit there, some cars have heater vents under the seat and the radio could overheat in the middle of winter! Also check "foot room" I'm sure you don't want an expensive transceiver used as a footrest by rear seat passengers.
The boot is also a common mounting place for the main unit, but ensure that the mounting position will not suffer undue dampness or get knocked about when the shopping is loaded. Also ensure adequate ventilation as a transceiver can get quite warm in use and inadequate ventilation may cause it to overheat or even melt the vehicles plastic trim if mounted touching it (worst case, hot enough to start a plastics fire! very unpleasant).
The microphone is another consideration, some can only be connected to the main unit (with an extension lead for remote use), some can connect to the remote head (ensure sufficient room for the plug/cable). Some radios with remote option can have the microphone connected to main or head units.
This really depends on the height of your vehicle, which band(s) you will be using and if you are willing to drill the roof or fit roofbars etc. The optimum position for a vehicle mounted antenna is the center of the vehicle roof (if the vehicle is of metal construction) as the vehicle body is used as the counterpoise (ground plane). Obviously if you are using HF with a decent sized antenna the roof will not be the best idea, thin steel not being the strongest mounting medium and bridges, power cables etc are best left alone!
Once these all things have been taken into consideration and the radio has been purchased, then the fun can start!
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.
If 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).
The power cable for the transceiver should be connected straight to the battery using cable that is rated higher than the rated consumption of the radio.
For long runs (i.e. radio main unit mounted in the rear of the vehicle, battery in the front) use even thicker cable, this will help to counter voltage drop over the length. (In my Yaris I have used alternator cable for my install as that's what I had handy (65Amp rated, radio draws less than 20 Amps max)).
Fuse the power cable at the battery with a weatherproof fuseholder. Also fit a fuse to the negative power lead if it is connected to the battery, because if the vehicles ground cable from the battery fails your engine could try to pull starting current through the coax and radio power lead! (not a pretty sight).
If you want the ignition switch to control the power to the radio then use a power relay to avoid overloading the ignition switch and to maintain the advantages of direct battery feed (see diagram below), make sure the relay switch contacts can handle at least the current your radio uses at full power.
Some people claim that running both the positive and negative wires from the battery and twisting them together helps to cut interference, others claim that using shielded cable helps to cut interference. In my experience (and recent industry standard advice) running the positive from the battery and the negative lead connected to a good ground point on the vehicle near the radio unit doesn't give much, if any, interference and is cost effective as you only run the one cable. Whichever way you choose make sure you fit the fuses and keep to the manufacturers ratings, exceeding these ratings can cause an electrical fire and your insurance company could refuse to pay out if they can prove the cause is "operator error".
Don't Do It! Don't be tempted to splice into a power cable that is already fitted, electrical noise from anything connected to that circuit can be annoying and the extra load could overload the circuit and cause a fire.
Use caution when routing wires between the passenger and engine compartments to avoid chafing or pinching of wires. Use grommets over any exposed sharp edges and strain reliefs to keep wires in place.
Seal all holes to prevent moisture and noise intrusion.
Route and secure all engine compartment wiring away from mechanical hazards such as exhaust manifolds and moving parts (steering shaft, throttle linkage, fans, etc.).
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!
If you use screws through the floor pan, put body sealer over the underbody projections, this will keep moisture out of the carpet and insulation, and will forestall rust in this area.
If you mount the radio under the instrument panel, be sure that there is no interference with proper operation of the foot controls (some vehicles have, for example, the brake pedal mounted on a long rod that operates the actual brake system on the other side of the vehicle from the driver).
Mount the control head (if seperate) and the microphone so that they are clear of the steering wheel, other controls and any airbags.
If the main unit is heavy, extra bracing may be needed for stability. Newer vehicles have more structure and energy absorbing materials and even airbags in the knee blocker (the lower part of the instrument panel).
Airbags are explosive devices.
Never fit anything to or in front of a panel that has an airbag behind it!
If fitting to a plastic instrument panel or other interior trim make sure that the mounting will be strong enough for the use you are giving it. You may need to fit large washers spread the load or a small steel plate to affix to behind the panel, a transceiver mounted to a plastic panel using self tapping screws may be easy, but the screws could pull through the plastic with the vibration of travelling, leaving the transceiver dangling on it's cables.
Nuts, bolts and spring washers are better than self tapping screws, especially if mounting to plastic. If using self tapping screws use spring washers to help counter the effects of vibration loosening them.
If your microphone is one that hangs on a hook it could rattle whilst on the move, which is very annoying (believe me). Just stick some sticky backed felt on the rear of the microphone or the panel it rests against to cushion it and it will rattle no more.
If you are lucky you can route internal cables through convenient cableways.
Here we see the cables for power (red),
control head and microphone (grey) that run
from the front of the car to the rear (where the
main unit is housed).
Here we see the trim has been replaced
and the cables have safely 'disappeared'.
Another way of securing cables is to wrap little 'flags' (see diagram below) of insulation tape around them and trap the free end of the 'flag' under the rubber door seal, it's not very pretty but it works.
Don't Do It! Tucking cables under the carpet or placing a mat over them is not a good idea, wear can still happen. A worn cable can short out and a fire could result.
Don't Do It! I have seen an I.C.E. install where the owner couldn't figure why he had no sound from one of his speakers. He had unscrewed the sill trim panel from the side of his car, run the speaker cable and replaced the sill trim, screwing it down. On testing the speaker it was OK so I traced the cable back. I came to the sill trim panel, I unscrewed the trim and discovered that he had put the screw straight through the middle of the cable, shorting both the live and return to ground (the amplifier used a seperate, isolated, ground for the speakers). It cost him a new amp (output blown, warranty void) and a new piece of speaker cable. He could have saved all that trouble for using a small piece of tape to hold the cable in place whilst he replaced the screw.
It is worthwhile remembering that if you can get the cables safely out of the way there is less likelihood of them being damaged but be careful doing it!
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.
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.
|HF:||Use C1 & C2 1.0µF|
|VHF:||Use L1 & L2 30µH, 7Amp rated|
|HF:||Use C1 & C2 1.0µF|
|VHF:||Use L1 - L5 30µH, 7Amp rated|
|If your wiper motor is only a single speed unit you omit C2 & L2.|
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!).