With the very wide range of car radio sets on the market, it is often difficult to know which to choose. However you can narrow down the selection even before looking at a catalogue or in a dealer’s window. First make up your mind how much you wish to spend – radios do vary considerably in price, depending on the quality. Decide whether you want a pre-set. push-button model or one which you tunc manually; the pre-set type is probably best for the motorist since you can easily select a programme without taking your attention off the road. If you want to use the radio outside the car as well, choose one of the combination models; these can be connected to run off the car battery, but can also be taken out and run off their own battery and speaker.
There is also the choice between AM and FM sets. AM stands for amplitude modulation and such sets operate on the long and medium wavebands; FM stands for frequency modulation and these sets operate on the VHF range. AM radios are much cheaper than FM ones, but are more subject to noise and interference; with FM sets, stereo transmissions can be received, but the range is limited and AM sets will usually pick up long range stations more clearly.
Most modern cars are negative earth: the negative terminal on the battery is connected to the car bodywork while the positive terminal feeds the lights and other electrical equipment. Before buying a radio, check it either matches the polarity of the car or that it can be changed over easily ; otherwise the set could be damaged.
MOUNTING THE RADIO
Many cars have a space in the dashboard for the radio; this is covered by a removable panel, which you unscrew or prise out, and the radio is mounted in the opening. If this is the case, make sure the set you buy will fit the space provided. Where the opening is too large, fit a mounting panel. If there is no space, mount the radio where you can operate it easily, but where it will not get in your way; a common method of mounting is on hanging brackets screwed securely to the underside of the dashboard; alternatively you can buy a centre console, which fits over the gear lever, to house the radio. When choosing the position for the radio, bear in mind the car’s electrical system and keep the set as far away from electric motors as possible; this will help reduce the amount of interference picked up by the radio.
Car radio kits are available which include all the necessary fittings together with suppressors for the electrical equipment; if you choose one of these. make sure you buy one suitable for your particular make of car.
CONNECTING UP The electricity supply for the radio can be provided in the same way as for any other accessory. However the best place of connection is to the radio terminal on the ignition switch, since this will enable you to operate the radio without having to turn on the ignition. Alternatively connect to an unswitched fuse in the fuse box, such as the one protecting the interior lights.
Check there is a fuse in the radio circuit; if not, fit a 3amp fuse in the main supply lead. Often the aerial will provide the earth for the radio, but it is a good idea to fit a separate earth lead to the radio body; this helps reduce interference.
CHOOSING AN AERIAL
The aerial is not usually supplied with the radio so you will have to buy one separately. Again there is a wide range available but, if possible, buy one recommended by the radio manufacturer. Most aerials are mounted on one of the front wings or on the roof; there are types which simply stick onto the windscreen, but these are lacking in performance and make interference suppression almost impossible. You can also buy glass fibre whip aerials, the top end of which clip to the car gutter; because of their length, these give better reception in fringe areas. Some aerials are fully retractable and motorized ones are also available.
Whichever type of aerial you choose, it must be of good quality to ensure the best possible reception from the radio.
INSTALLATION Before fitting the aerial, turn on the car engine, switch on the radio and plug in the aerial. Holding the aerial by the insulation at the bottom, walk round the car to discover where interference is at its lowest and fit the aerial accordingly. Manufacturers supply fitting instructions and often advise on the most suitable mounting place. Always pay attention to these instructions for the best results.
It is essential the aerial is securely mounted and that it makes a really efficient earth connection. You will need to make a hole in the car bodywork in order to fit the aerial; use a drill to make a pilot hole and finish off with a round file, working carefully to avoid damaging the bodywork. Fit the aerial with the washers and securing nut supplied; take care not to overtighten the nut or you may damage the bodywork – and the aerial. Pass the lead through to the inside of the car. You should find a hole already prepared at the back of the engine compartment. Check the hole is lined or fit a rubber grommet to protect the lead where it passes through the bodywork. If the lead is not long enough to reach the radio, buy a suitable extension and join up with a connector.
Speakers are usually supplied with the radio, either singly or in pairs; they come with or without grilles and mountings. If you buy the speaker separately, make sure it has the correct impedence rating for your radio.
You may find there is already provision in the car for a speaker ; if not, you must decide for yourself where to mount it and follow the manufacturer’s fitting instructions.
If you are fitting two speakers, try to mount them so there is an even distribution of sound – at each end of the rear parcel shelf is a good position. Speakers can also be mounted in the doors or on opposite sides of the car on the front parcel shelf or below it.
In any case, always ensure the speaker cone does not touch any part of the bodywork and that the speaker casing is securely fitted, but not’in direct -contact with metal; an insulating gasket should be fitted between the casing and the mounting panel to eliminate vibration when the speaker is in use. If – the speaker is mounted face up, place apiece of thin cotton mesh or similar material under the grille to prevent dirt and dust accumulating. When fitting two stereo speakers; ensure they are in phase. This simply involves checking the wireSi connected to each are the right way found’. If the sound is woolly with poor bass response, change the connections on one of the speakers and it will improve.
Trimming the radio
Most car radios have a trimming device which tunes the radio to suit the car and the aerial. This can be adjusted to give the best reception by turning a small screw, usually behind or alongside the tuning knob; you may have to remove the tuning knob to gain access to it Turn the screw, with a suitable screwdriver, in either direction to find the point at which the best possible reception is obtained for any given radio station