Reception


Your radio or your location may not be to blame when you can't seem to get rid of noise or find few stations across the radio dial. This section will cover the most common problems and solutions for antenna reception.

First, make sure you have all the pieces to the "puzzle". Before you even worry about optimum reception, you must have an acceptable antenna and related hardware. There's no way a radio is going to perform well in a vehicle with an antenna lead that is kinked and scarred, a bent or broken mast or moisture damaged components. If body work was recently done, and little care was taken, there may be a damaged spot in the antenna lead or connector hidden behind a body panel.

Before you start pulling wires and disassembling things, check the below descriptions for ideas on tracking down an antenna problem.

If you are unfamiliar with these descriptions or vehicle audio/electrical equipment, please see qualified service personnel. It is always a good idea to disconnect the negative (-) battery cable before working on vehicle electrical components.



NO RECEPTION

While it may seem pointless, check the obvious first. If there is an antenna mast, is it raised? Is the antenna plug connected to the radio? If so, is it firmly seated in the connector? Is there any antenna lead at all or did a careless former owner cut it off?

   

The antenna connector plugs into the rear of the radio (the lower corner on the passenger side). The combination radio/8-track players have their antenna jack in the rear center. Check the condition of both the connector and coaxial cable, as both provide the antenna connection and a shield against electrical interference. They both need to be in good shape.



WINDSHIELD ANTENNAS

The factory windshield antennas on 1970-1972 Chevelles, El Caminos, Monte Carlos, and related vehicles are quite reliable. When things don't appear to work right, the connections and hardware should be checked before suspecting the windshield itself (unless the glass has an obvious fault like a crack/shatter). If you are having your 1970-1972 vehicle's windshield replaced, make sure you take it to a competent glass installer and specify you want a windshield with the built-in "invisible" radio antenna because not all 1970-1972's (radio delete vehicles for example) have these windshields with built-in antennas.

When picking-up the vehicle, check to see if the radio works properly, as some of the modern glass adhesives can actually short-out antenna connections or a hasty installation could mean the antenna pigtail itself was not plugged into the cowl connector! Check it before you leave to save yourself time and money.



After removing the stainless steel trim at the base of the windshield, it is easy to see the pigtail connector located at the bottom center of the glass (this one is obviously unplugged). This is what links the radio to the tiny leads inside the glass. The pigtail must be firmly connected into the cowl connector and both should be free of dirt/corrosion to provide a reliable antenna connection. (Please note: The metal connection plate at the bottom of the windshield is normally covered with sealant. This has been removed in the above picture).



TRIMMER ADJUSTMENTS

On all factory radios there is a "trimmer" adjustment screw that is used to optimize AM reception by properly trimming the antenna (electronically). Normally this needs little or no adjustment, but when radio and antenna components get swapped or reception is constantly poor despite a normally operating radio, it may be necessary to use this adjustment.



Follow these steps to adjust the trimmer:

1) Turn on the radio and tune to a weak station on or near 1400 kHz on the AM dial while the engine is off. Make sure there is ample volume so you can hear any differences while adjusting the trimmer. This process should be done in a fairly open area where large objects aren't around to affect normal reception.

2) Make sure all the sheet metal on the car is in place and shut the doors. Remove the tuning knob and knob behind it from the radio. Above the tuning control shaft you will see a small hole, inside is the trimmer adjustment. (Use the above picture as a guide).

3) Use a very small screwdriver that will fit the adjustment screw inside. Because the screwdriver is metal, you will have to make only slight turns at a time and then pull the screwdriver out each time (the screwdriver is metallic and slightly alters the trimming process) before listening to the radio's output from the speaker(s).

4) The idea is not to tighten or loosen the screw completely (remember this is a fragile component), just turn it a little in a direction that gives you the loudest output from the weak station tuned in.

5) Once you have the antenna "trimmed" properly (loudest output achieved), don't adjust the antenna itself (raise or lower the mast if it's telescopic) or you will have to repeat the process again for optimum reception. If you have a windshield antenna, this process can also optimize your reception. If you have a factory rear power antenna, don't worry about "loosing your settings" because the antenna should always extend to the full length every time the radio is on.

6) Install the knobs back on the radio.



ANNOYING INTERFERENCE

This can take some time to track down depending on the all the things which have to be taken into consideration. If a radio appears to be working correctly and receiving different stations across the dial, but there are unwanted noises (whining, crackling/popping, hissing, etc.) heard, some investigative work will have to be done.

In the stock form, the vehicles with factory radios installed came equipped with such items as:

-"Radio suppression" spark-plug wires

-Capacitors installed on such items as voltage regulators and ignition coils ***

-Shielded and grounded connectors and leads

-Ground straps on engine and chassis components

-Vehicle/component designs that placed potential interference sources as far as possible from radio/antenna equipment.

All of these items (except the capacitors) were intended for one purpose, prevent unwanted noise on the radio caused by electrial circuits in the vehicle which can emit RFI (radio frequency interference) waves.

***Capacitors (commonly referred to as condensers) were installed to cancel-out "noise" caused by the reactive portion of electromagnetic inductors (coils of wire found in ignition coils, voltage regulators, blower motors, etc.). As the electromagnetic field "fades" after power is disconnected from an inductor, it tries to act like a generator "feeding" electricity back into the vehicle circuits. Capacitors are used to "cancel" this reactive portion out. Without them, noise would be heard on the radio via its power circuit connection--not through it's antenna like RF interference.

Typical interference problems:

COMPLAINT:
Whining noise heard in the speaker(s) when the engine is running.

POSSIBLE CAUSE:
A) Bad grounds at one or both ends of the antenna lead and/or bad ground connection at the radio.
B) Alternator/voltage regulator is beginning to fail.

COMPLAINT:
Crackling/popping noises heard when engine is running (intensifies when engine increases in rpm).

POSSIBLE CAUSE:
A) Bad grounds at one or both ends of the antenna lead and/or bad ground connection at the radio.
B) Poor quality spark plug wires that don't have ample radio frequency suppression. Use types with "suppresion cores".
C) Check ignition components (e.g. check to see if the distributor's dwell adjustment "trap door" is fully closed, the correct external condensor is connected to the stock ignition coil, etc.).

COMPLAINT:
Noises or static heard when certain electrical accessories are turned on.

POSSIBLE CAUSE:
A) Bad grounds at electrical accessories or antenna connections.
B) See the notes below.


IMPORTANT NOTES:

Most people think that a simple "in-line noise filter" that typically splices into the radio's power circuit will eliminate any and all noise. Unfortunately, this usually solves few problems. These noise filters are ideal for filtering out "interference" caused by such items as blower motors that want to act as generators "feeding" electricity back into the vehicle's circuits. Most interference complaints result from stray RF (radio frequency). RF from items such as ignition components received on radio through antenna components and not through the actual electrical system. Sometimes the most difficult part about finding the source of interference is first determining whether the noise is RF related or not. Take notes when specific noises are heard--whether it is heard all the time, only when certain accessories are on, increases with engine rpm, etc. to help pin-point the source. It may be necessary to re-route aftermarket accessories/wiring to reduce noise.


Lastly, despite attempts to solve problems (see the Antenna Parts section for more help), you may have to "live" with unwanted radio interference if...

-Your vehicle has been altered (e.g. fiberglass body parts installed).

-You have fitted your vehicle with electronic upgrades (e.g. fuel injection, high-output ignition systems, etc.).

-You have added or altered vehicle wiring (e.g. installed a tachometer/related wiring close to radio equipment, added audio amplifiers, etc.).

-You have intalled a modern aftermarket radio (modern technology holds many benefits, yet the AM band may not be as clear as you want because many modern units lack the same quality in "noise filtering" and tuning circuits).

-You live in an area with a lot of stray radio frequency interference (near high-tension power lines, large electrical machinery, etc.).



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