Mobile Installation guide.

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:

What bands do you want to use:
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?

Ease of use:
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!

Where to fit it:
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 headlining 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.

Antenna Mounting:
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!

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.

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 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.).

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).

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.
Routing Cables:

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!

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 minimize 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:

Avoid running the cable near other vehicle wiring, especially wiring that connects to the vehicle's electronic control modules.

Coaxial cable is not 100% shielded, so there will be some RF leakage from the cable. Look for coaxial cable that has a higher percentage of shielding, the closer to 100%, the better. I personally favour the 'Mini-8' RG-8X coax which is 95% shielded, flexible and not too expensive, although it is slightly larger diameter than RG-58 and may need some 'thining' when fitting to the antenna mount. Special PL259 plugs are available with the larger hole.

Always use a single piece of coaxial cable, joins not only give physical weakness (vibration disconnection) but cause losses and a possible point for corrosion to set in as well.

Connector quality and termination techniques are just as important, it's no good connecting an expensive piece of coax with a 10 pence plug and expecting top performance.

Don't Do It! Don't use the 'Quick and Dirty' method of fitting a PL259! See Fitting a PL259 for the proper way to fit them.
Avoid sharp edges and pinches and keep the cable as short as possible.
Care should be used in mounting antennas with magnet bases. Magnets may affect the accuracy or operation of the compass on vehicles so equipped, also magnetic bases can scratch the paintwork if not placed and removed with care.
Carefully match the antenna and cable to the radio to ensure a low Standing Wave Ratio (SWR). See SWR Description & How To.

Physical Mounting:

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

For boot lid installations, the boot lid must be bonded to the body, that is electrically joined, with short braid straps (suitable straps can be fashioned from coax braid and a couple of ring terminals). These must connect to clean sheet metal at both ends. For AM/SSB and even some FM installations, the bonnet must be bonded to the body. In some cases the doors may need to be bonded as well.
Glass-mount antennas will not work or will only work very poorly in vehicles with metallized glass (Electrically-heated windshields or some solar reflective glass) (I find this type of antenna doesn't work too well anyway!) and need refitting in the event of a broken window (you need to clean off all the broken shards too!).
Non-metallic bodies require a half-wavelength antenna or a ground plane with radius at least approximately equal to the length of a quarter-wave antenna. Copper is the best choice, but aluminium or even steel may be used. Install on the inside of the body panel with a good adhesive or tape and provide a good RF connection to the coax shield at the feedpoint. Screen, mesh or thin sheet stock may be used. Shape is not critical, but some directional characteristics may be noted if it is not round.
Consider the sunroof mechanism for physical interference to the antenna base and the coax if roof mounting to a car with a sun roof.
For HF antennas, refer to the manufacturer's instructions and follow them closely, unless you are an accomplished antenna experimenter. HF antennas should be mounted to body or frame steel for a good counterpoise as well as structural strength. A steel plate 15cm or so larger than the antenna base on the inside of the bodywork (if there is room) will add structural strength.
Make sure that the shield of the coax is well grounded at the antenna base, this may mean sanding the inside area of the bodywork to remove paint and anti-rust layers.
If mounting through the bodywork make sure that you seal the outside against water ingress. A rubber washer can be fashioned from an old inner tube (make sure the hole is a tight fit around the base). Some silicone sealer is another option. You don't want water inside the vehicle, it will corrode the antenna connection and the upholstery, carpet etc. will start to smell musty. Remember: fit the rubber washer or sealant to the outside of the bodywork as the coax will be grounding on the inside and you can't ground to rubber.
If mounting to a roof bar ensure that all mounting clamps are tight, check at regular intervals, and ensure that the bar is bonded to the bodywork, you may need to fit braid straps for this (suitable straps can be fashioned from coax braid and a couple of ring terminals).

Interference:

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.

I've encountered a problem with some cars that, although made from steel, the bonnet was a plastic composite and didn't shield the engine electrics, causing all sorts of noise on the receiver. This was cured with aluminium foil (baking foil) glued to the underside of the bonnet and bonded to the cars steel body. Where the foil sheet needed to 'join' I glued the first piece over one of the ribs that made the bonnet rigid and the second piece was not totally glued where it overlapped on the rib, it was secured with a small nut & bolt with flat washers (glue would be an insulator), the same nut and bolt method was used for the bonding cable (see diagram).
A whining that rise and lowers in pitch in time with engine speed is generally caused by the alternator.
- The problem could be that the alternator is not grounded properly. The cure is to get a good sized grounding strap from an accessory store or motorfactor and connect the alternator casing straight to the vehicle body. Some alternators have a grounding post on the rear case for this. Make sure that the body end is connected to a good clean ground and that the strap is well away from moving parts.
- The problem could also be caused by a faulty diode inside the alternator, the alternator will appear to work fine with a faulty diode but the problem is there. A possible cure is a large capacitor across the output from the alternator (mounted as close to the alternator as possible, on the rear casing is best).
Any electric motor can cause a crackling or receive or transmit or both. Most small electric motors in vehicles are permanent magnet motors. Some possible cures are:
- Heater, Radiator cooler. Make sure the metal casing (if it has one!) is well grounded. If the motor is all plastic and gives interference you could try covering the motor housing with glued down foil and grounding the foil (see Plastic Bonnet above). Add C1 & C2 or L1 & L2 (all if all band suppression is required).
  
  HF: Use C1 & C2 1.0µF
  VHF: Use L1 & L2 30µH, 7Amp rated
- For wiper motors it is a little more complex as they have the self park function:
  
  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.

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.

One Final 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!

General notes for mobile transceiver fitting.

First considerations:Choosing the right radio:

Fitting: Transceiver:

Physical Mounting:

Routing Cables:

Fitting: Antenna:

Routing Coax:

Physical Mounting:

Interference:

One Final Tip:

First considerations:
Choosing the right radio: