Radio Reception
POOR RECEPTIONIf poor radio reception occurs:
^ Make sure automatic power electric antenna, if equipped, is fully extended.
^ For either antenna, make sure the cable connections are secure.
ANTENNA POSITION
The electric antenna will adjust to the full extended height for best FM reception.
^ FM stereo has a range of about 32 km (20 miles) before interference noises are heard.
^ This means that in concern areas with tall buildings or hills, it is necessary to select the strongest possible station.
^ The electronic radio receiver automatically tunes to the center of any given station, eliminating the need for manual fine tuning.
ANTENNAS AND MOBILITY
Although an automotive radio receiver 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 automotive FM reception, the antenna system should be designed like a television 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 automobile 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 receiver.
TUNING
Fine tuning is not required for the radio receiver. The electronic radio receiver automatically tunes to the center of the station where it will obtain minimum noise and best possible reception.
TONE CONTROL
Reducing the amount of treble can improve sound quality when receiving weak signals.
FM FLUTTER
Flutter can be characterized as repeated pops, hissing and bursts heard in the radio speaker during an otherwise good broadcast. This condition usually 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 receiver 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. 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 tuning control. When passing the tower, the station may switch back and forth a few times before returning to the station originally tuned.
A localized condition which will not harm the radio receiver is known as overloading.
^ When several broadcast towers are present (common in metropolitan areas), several stations may overload the receiver resulting in considerable station changing, mixing and distortion.
^ 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 stereo.
^ The AM/FM stereo radio receiver 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 concerns, 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 receiver to a nearby FM stereo station. If reception is good but stereo indicator is still intermittent, remove the remote chassis unit for service.
INTERFERING NOISES
There are many possible sources of radio interference:
^ One source is the vehicle ignition system. This high-voltage switching system produces a radio frequency electromagnetic field that radiates at AM, FM and OB frequencies. Although components have been designed into the vehicle to minimize this concern, the noise is more noticeable if the radio receiver is tuned to a weak or distant channel when listening to FM programs.
^ Vehicle electrical accessories and owner add-on accessories may also contribute to radio receiver interference.
IGNITION NOISE
The most effective method of evaluating ignition noise is to compare the radio chassis performance with the engine running, versus engine off. If ignition noise is present with engine running:
^ Check to see that the ignition wires are the suppressor type and that the spark plugs are the correct resistor type.
^ Check to see that spark plug wires are fully seated on spark plugs.
^ check to see that spark plugs are properly gapped and seated in cylinder heads.
MISSING OR DAMAGED NOISE SUPPRESSION COMPONENTS
^ Noise suppression components may be damaged or mission.
^ Check radio frequency interference suppression bond grounding effectiveness by wedging a large fire between metal parts to make sure of proper ground, such as between the fender and frame, while the radio receiver is playing and engine is running.
^ Listen for a decrease in the objection 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 radio frequency interference suppression bond between the two metal parts to make sure of proper ground.