Radio Reception

Antenna Position

The antenna is fixed and not adjustable.

The AM and FM stereo antenna has a range of about 32 km (20 miles) before interference noises are heard. This means that in areas with tall buildings or hills, it is necessary to select the strongest possible station. The electronic radio chassis (18806) automatically tunes to the center of any given station, eliminating the need for manual fine tuning.

Antennas and Mobility

Although a vehicle radio will give outstanding mobile reception, it cannot provide the continuous reception of home audio components. The home receiver is not limited by the vehicle operating characteristics and certain geographical effects as is the mobile unit. For example, for the best FM reception, the vehicle antenna should be designed similar to a TV antenna and pointed in the direction of the station. The best AM antenna is a long piece of wire; the higher the wire the better the reception. However, because of design necessity, the vehicle antenna is restricted in size, height and direction and must receive both AM and FM stations. This means that a limited amount of the station's signal reaches the vehicle radio.

Tuning

The electronic radio automatically tunes to the center of station frequency.

FM multiplex has a range of about 32 km (20 miles) before reception noises are heard. This means that in areas with tall buildings or hills it is necessary to select the strongest possible station.

Experience will dictate which FM stations offer the best reception.

Tone Control

Turn the single tone control on AM radios clockwise to decrease bass (low frequencies) and turn counterclockwise to decrease the treble (high frequencies).

Refer to Audio System Operating Guide for AM/FM radio tone control adjustment procedure.

FM Flutter

Flutter can best be described as repeated pops and hissing bursts heard in the radio speaker (18808) during an otherwise good broadcast. Usually this condition exists while traveling in the fringe area of the station. Flutter will become more severe beyond approximately 40 km (25 miles) of the station. The signal loss becomes greater away from the station, until finally noise takes over and reception becomes impossible. Flutter may also be noticed near the station because of the line-of-sight characteristics of FM radio waves. This condition can happen when a building or large structure is between the radio chassis and the station being received. Some of the FM signal bends around the building, but certain spots have almost no signal. Some of these signal losses are only a few inches wide and if the vehicle is parked in one of these dead spots, you will only hear noise from the radio speaker. After moving out of the shadow of the structure, the station will return to normal. Flutter will not occur on AM because the AM radio waves are much longer than FM waves.

FM Multi-Path Cancellation

Another effect caused by the line-of-sight characteristic is called cancellation. This condition exists when the radio waves are reflected from objects or structures. The noise produced by cancellation is similar to flutter, with the addition of distortion in the program. A more familiar description of cancellation is its similarity to the multiple ghosts and picture jumping that occurs on television when a low flying plane passes. The same condition exists in the vehicle, except that the vehicle is moving and the reflecting structure is stationary. The reflected signal cancels the normal signal, causing the antenna to pick up noise and distortion. Cancellation effects are most prominent in metropolitan areas, but can also become quite severe in hilly terrain and depressed roadways.

FM Strong Signal Capture and AM Overloading

FM capture is an unusual condition that occurs when traveling in the vicinity of a broadcast tower. If listening to a weak FM station when passing the broadcast tower, a stronger station may interfere without changing the radio dial. When passing the tower, the station may switch back and forth a few times before returning to the station originally tuned. When several broadcast towers are present (common in metropolitan areas) several stations may overload the receiver resulting in considerable station changing, mixing and distortion. Fortunately, this condition is localized and it will not harm the receiver. Some overloading may also be noticed on AM, but usually to a lesser degree.

Receiving FM Stereo

Because more data is carried in the FM stereo waves than in the monaural FM broadcasts, flutter, cancellation and capture are even more noticeable. The FM stereo noise-free broadcast range is approximately 8 km (5 miles) less than that received with the monaural FM radio. The AM/FM, FM stereo radio may never encounter any of these troublesome conditions, as they are more prominent in metropolitan areas, hilly terrain and depressed roadways. However, when diagnosing FM stereo, it is recommended to accurately tune to the strongest FM stereo station.

Stereo Indicator Inoperative or Flickering (AM and FM Reception Are OK)

Verify that customer is listening to stereo stations.

A weak or distant signal may cause the stereo indicator to flicker. Tune radio to a nearby FM stereo station. If reception is good, but stereo indicator is still intermittent, remove radio chassis for service.

Radio Tests

Internal diagnostic examination of the radio chassis should be left to the authorized radio service center. However, the automotive technician should be able to analyze and isolate radio chassis reception conditions to the proper area or component causing the condition. All radio chassis conditions can be isolated to one of five general areas:

• Antenna system.
• Radio chassis.
• Radio speaker system.
• Radio noise suppression equipment.
• Radio amplifier.

Interfering Noises

The vehicle ignition system is a source of radio interference. This high-voltage switching system produces a radio frequency electromagnetic field that radiates at AM, FM and CB frequencies. Although components have been designed into the vehicle to minimize this concern, the noise is more noticeable if the radio is tuned slightly off channel for FM programs. Vehicle electrical accessories and owner add-on accessories may also contribute to radio interference. Furthermore, there are many noise sources that are external to the vehicle. These include power lines, communication systems, ignition systems of other vehicles, neon signs, etc.

Favoring the rear radio speaker in noisy areas will help to reduce noise.

Ignition Noise

The most effective method of evaluating ignition noise is to compare the radio performance with the engine on, versus engine off. If ignition noise is present with engine running:

• Check to see that the spark plug wires are the suppressor type and that the spark plugs are the correct resistor type.
• If so equipped, check to see that the carbon center insert in distributor cap (12106) is secure.

  NOTE: Silicone grease must not be removed from vehicles equipped with electronic engine controls (EEC-IV).

• If so equipped, check distributor cap and rotor electrodes for silicone grease, as this may cause ignition noise on FM. This noise is characterized by a "motor boat" type sound on weak to moderate strength stations. The noise can only be eliminated by replacing the distributor cap and distributor rotor (12200) with a cap and rotor that do not have grease.

Missing or Poor Grounds

Check bond strap grounding effectiveness by wedging a large file between metal parts to ensure proper ground, such as between the tail pipe and body, or between the fender and frame, while the radio chassis is playing and the engine is running. Listen for a decrease in the objectionable radio noise. If a reduction in radio noise is noted, first try tightening body and exhaust system clamps and brackets. Then, if necessary, install a new bond strap between the two metal parts to ensure proper ground.

Missing or Damaged Noise Suppression Components

Noise suppression components may be malfunctioning or missing. Service or replace any missing or damaged components.

Sound Distortion, Premium Sound

Sound distortion can be attributed to any of three components: the radio amplifier (18B849), the radio chassis, or the radio amplifier wiring (19B113) that connects the radio amplifier to the radio chassis. If any of these components is damaged, sound quality will be distorted. The speakers will also cause distortion if any of them are grounded (CDR only). Refer to the Symptom Chart in this section for diagnosis and testing procedures.