Porsche 911 Carrera Manual page 136

Car Audio Operation/Tips
FM reception
A vehicle is not an ideal place to listen to a radio.
Because the vehicle moves, reception conditions
are constantly changing.
Buildings, terrain, signal distance and noise from
other vehicles are all working against good recep-
tion.
Some conditions affecting FM may appear to be
problems when they are not.
The following characteristics are completely nor-
mal for a given reception area, and they do not in-
dicate any problem with the radio itself.
Note
Electronic accessories should only be installed by
your authorized Porsche dealer.
Equipment which has not been tested and ap-
proved by Porsche may impair radio reception.
136
Controls, Instruments
Fading and drifting
FM range is limited to about 25 miles (40 km),
except for some high power stations.
If a vehicle is moving away from the desired sta-
tion's transmitter, the signal will tend to fade and/
or drift. This condition is more prevalent with FM
than AM, and is often accompanied by distortion.
Fading and drifting can be minimized to a certain
degree by careful attention to fine tuning or selec-
tion of a stronger signal.
Static and fluttering
When the line-of-sight link between a transmitter
and vehicle is blocked by large buildings or moun-
tains, the radio sound may be accompanied with
static or fluttering because of the characteristic of
FM.
In a similar effect, a fluttering noise is sometimes
heard when driving along a tree-lined road.
This static and fluttering can be reduced by adjust-
ing the tone control for greater bass response un-
til the disturbance has passed.
Multipath
Because of the reflecting characteristics of FM,
direct and reflected signals may reach the antenna
at the same time (multipath) and cancel each other
out.
As a vehicle moves through these electronic dead
spots, the listener may hear a momentary flutter
or loss of reception.
Station swapping
When two FM stations are close to each other, and
an electronic dead spot, such as static or multi-
path area, interrupts the original signal, some-
times the stronger second signal will be selected
automatically until the original one returns.
This swapping can also occur as you drive away
from the selected station and approach another
station of a stronger signal.