Diagnosis And Testing; Antenna; Audio System - Jeep 1996 Grand Cherokee Service Manual

ZJ
DESCRIPTION AND OPERATION (Continued)
tweeter mounted in each outboard end of the top of
the instrument panel.

ANTENNA

All models use a fixed-length stainless steel rod-
type antenna mast, installed at the right front fender
of the vehicle. The antenna mast is connected to the
center wire of the coaxial antenna cable and is not
grounded to any part of the vehicle.
To eliminate static, the antenna base must have a
good ground. The coaxial antenna cable shield (the
outer wire mesh of the cable) is grounded to the
antenna base and the radio chassis. The antenna
cable has an additional disconnect, located near the
right end of the instrument panel and the right cowl
side panel, to allow instrument panel installation
and removal without removing the radio.
The factory-installed ETRs automatically compen-
sate for radio antenna trim. Therefore, no antenna
trimmer adjustment is required or possible when
replacing the receiver or the antenna.
RADIO NOISE SUPPRESSION
Radio Frequency Interference (RFI) and Electro-
Magnetic Interference (EMI) noise suppression is
accomplished primarily through circuitry internal to
the radio receivers. These internal suppression
devices are only serviced as part of the radio receiver.
External suppression devices that are serviced, and
should be checked in the case of RFI or EMI noise
complaints, include the following:
• Radio antenna base ground
• Radio chassis ground wire, strap, or bracket
• Engine-to-body ground strap (if equipped)
• Cab-to-bed ground strap (if equipped)
• Heater core ground strap (if equipped)
• Resistor-type spark plugs
• Radio suppression-type secondary ignition wir-
ing.
In addition, if the source of RFI or EMI noise is
identified as a component on the vehicle (i.e., gener-
ator, blower motor, etc.), the ground path for that
component should be checked. If excessive resistance
is found in that circuit, repair that circuit as
required before considering any component replace-
ment.
If the source of the noise is identified as two-way
mobile radio or telephone equipment, check the fol-
lowing:
• Power connections should be made directly to
the battery, and fused as closely to the battery as
possible.
• The antenna should be mounted on the roof or
toward the rear of the vehicle. Remember that mag-
netic antenna mounts on the roof panel can adversely
affect the operation of an overhead console compass,
if the vehicle is so equipped.
• The antenna cable should be fully shielded coax-
ial cable, should be as short as is practical, and
should be routed away from the vehicle wiring when-
ever possible.
• The antenna and cable must be carefully
matched to ensure a low Standing Wave Ratio
(SWR).
Fleet vehicles are available with an extra-cost RFI-
suppressed Powertrain Control Module (PCM). This
unit reduces interference generated by the PCM on
some radio frequencies used in two-way radio com-
munications. However, this unit will not resolve com-
plaints of RFI in the commercial AM or FM radio
frequency ranges.

DIAGNOSIS AND TESTING

AUDIO SYSTEM

WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, REFER TO
RESTRAINT SYSTEMS
STEERING WHEEL,
INSTRUMENT PANEL COMPONENT DIAGNOSIS OR
SERVICE. FAILURE TO TAKE THE PROPER PRE-
CAUTIONS COULD RESULT IN ACCIDENTAL AIR-
BAG DEPLOYMENT AND POSSIBLE PERSONAL
INJURY.
AUDIO SYSTEMS
GROUP 8M - PASSIVE
BEFORE ATTEMPTING
STEERING COLUMN,
8F - 3
OR