Radio - Poor Reception Vehicles W/Rear Window Antenna: Overview

GROUP 65
Radio and Accessories

Bulletin Number
65 11 88 (1736)

Woodcliff Lake, NJ
January 1989
Technical Dept.

SUBJECT:
Radio Reception

MODELS:
All equipped with rear window antennas

This bulletin addresses the issue of poor radio reception on vehicles with rear window antennas. Read this bulletin thoroughly, to familiarize yourself with this subject and to be able to address customer's questions on radio reception.

Situation:
Quite often customers compare and expect the same level of radio reception in their car as they do on their radio at home.

In reality there are considerable differences. First the physical size of a home antenna is usually much larger than an automobile's.

Secondly, the home antenna is usually mounted to the highest point on the roof. In comparison the automobile antenna is close to the ground and is usually in motion.

With the automobile/antenna in motion, reception difficulties not apparent on a home unit can be heard. These are usually experienced when traveling next to tall buildings, going through tunnels or over bridges and when traveling through hilly terrain. All of these traits (dead spots, multipath, fade and station swapping) become more apparent with a weaker signal.

These differences, when explained to the customer, can help him/her accept the occasional reception difference in his/her automobile.

Remedy:
In addition to the normal running changes taking place in production, an improved antenna amplifier was phased into production during 5/88.

The new amplifier should be fitted to those vehicles not so equipped when justifiable reception complaints arise.

It is mandatory that the procedures outlined in the listed S.I. bulletins are followed before Installing this new amplifier. (Copies of the S.I. procedures are attached).

65 06 87 (1440) - Antenna/Antenna Amplifier Diagnosis
65 05 87 (1436) - Poor Radio Reception - AM Band
65 09 87 (1460) - Antenna Cable Testing Procedures

If a problem exists in one of these areas, it will still remain after the new amplifier has been installed.



In isolated cases, a properly working rear window antenna with the improved antenna amplifier may not bring the reception to the level the customer demands. This can be the case particularly on the FM band in fringe reception areas.

For those instances an electric mast antenna may be fitted to the left quarter panel.

Both antenna systems (rear window/mast) have their own benefits and disadvantages. These must be explained to the customer before a mast antenna is installed.

Proper questioning of the customer before the installation of a mast antenna is the only way to ensure that he/she is a proper candidate for this installation.

Familiarize yourself with the following points to aid in this determination.

^ First, if the customer is only complaining about poor AM reception, the problem lies somewhere in the rear window/coax system. Refer to the attachments for diagnosis.

A mast antenna does not offer improved AM reception in comparison to a properly working window system.

^ Second, the rear window antenna is superior to the mast antenna in eliminating strong signal problems usually encountered in city driving (close to transmitter). It is also less susceptible to outside interferences which is heard as static through the speakers. If the customer drives predominately In the city, the rear window antenna is definitely the superior system.

^ Third is the issue of styling and maintenance of the mast antenna. It must be pointed out to the customer that they must keep the mast clean to ensure proper operation and the mast must be lowered (radio turned OFF) to avoid breakage in car washes, parking garages, etc.

The area where the mast antenna can be helpful is in fringe reception areas on FM and WB. For FM this would be a distance greater than 40 miles from the transmitter. The customers complaint may be that while traveling in one direction, the reception is acceptable, but when changing directions, the station fades away. This is due to the fact that the rear window antenna is somewhat directional - dependent in these bands in areas of low signal strength.

If it is decided to install a mast antenna use the installation procedures listed in attachment IV. (The procedures supplied with the mast antenna may list incorrect measurements.)