RX7 2RTR- 1308cc 1.3L FI (1987)
Radio/Stereo: All Technical Service Bulletins
Radio - Normal Conditions of FM & AM Reception
Category
Applicable Model/s
Subject
Bulletin No.. 050/87
15
All Models
NORMAL CONDITIONS OF FM & AM
Issued
9/10/87
RADIO RECEPTION
Revised
DESCRIPTION
Radio reception in a moving vehicle is more difficult to control than in a fixed location such as a home. Often times when customers have a complaint
about the radio in their vehicle, the problem is simply one of normal operation.
Careful explanation of normal radio operation and limits of the audio system will increase consumer awareness and satisfaction. Such explanations can
also reduce unnecessary repairs and inconvenience to the customer.
The following are brief explanations of conditions encountered with radios in vehicles.
FM RECEPTION IN VEHICLES
FM broadcast range is generally about 25-30 miles from the source. Due to extra coding needed to break the sound into two channels, stereo FM has
even less range than monaural (non-stereo) FM. Signals from an FM transmitter are similar to beams of light because they don't bend around corners, but
they do reflect. Unlike AM signals, FM signals cannot travel beyond the horizon. Therefore FM stations cannot be received at the great distances
possible with AM reception.
Imagine an FM transmitter as a long pole with a light bulb mounted at the top. Anything (such as buildings, landscape, or even the horizon) coming
between the bulb and person viewing blocks out the light just as the FM signal would be blocked from directly reaching the radio.
Atmospheric conditions can also affect FM reception. High humidity will cause poor reception. However, cloudy days provide better reception than clear
days.
Different characteristics of FM and AM broadcasts. Note how AM signal can travel beyond the horizon while FM cannot.
UNAVOIDABLE NOISES
1.
Multipath Noise:
Since FM signals can be reflected by obstructions, it is possible to receive both the direct signal and reflected signal at the same time. This causes a
slight delay in reception and may be heard as a broken sound or distortion. This problem can be encountered even at close proximity to the
transmitter.