You can easily check for several things to identify the cause of the interference. The origin of car radio interference is in the ignition system, electrical accessories, or the charging circuit. Interference can either be radiated or conducted to the set by its wiring. Being radiated means that it is picked up by the aerial.
Your radio was fine, but all of a sudden, it stopped being clear because of the annoying radio interference. But don’t worry, as we’ll let you know how to identify and suppress car radio interference.
Identifying the source of radio interference
There are several ways you can identify and suppress radio interference. Before you look for the cause of the annoying radio interference, remember to make sure that the set is earthed to the metal bodywork of your car.
Examining the aerial mounting
It should have a firm and clean contact with your car’s underside, so the earth connection is successful. Remember to clean and check the car’s underside beforehand so it’s easier to check the connection.
Crackling or ticking noise
A ticking or crackling noise is an easy indication that your car radio has interference. A rapid crackling or ticking noise that increases and gets worse with the engine speed confirms that the issue is coming from the ignition system. An ignition system is a common reason for car radio interference.
The ticking sound comes from the low tension parts, and the crackling comes from the high tension side.
If your car sputters then that is a different issue.
A whining sound comes from the dynamo or alternator that is not properly fitted with a suppressor. This whining sound increases in pitch with the increase in engine speed. An improperly fitted dynamo may cause problems. Remember to remove and refit a dynamo pulley properly if its suppressor is loose. If the issue is with the brushes then replace the dynamo brushes.
Interference from electrical components
Electrical components can cause interference as well. Electrical components like windshield wipers, car heater, or an indicator are common causes for radio interference as well when they’re turned on. When any of these electrical components are turned off, any noise that is coming will go away.
Remember to check the car’s wiring system whenever you’re working on it every now and then. It can always come in handy for fitting new connections and finding faults.
Disc brakes, when applied, can also be a cause of car radio interference.
Wiring or power supply
Power supply or wiring of the speakers can be a common radio interference reason, too, if they’re passing very close to the magnetic field of other electronic components. To solve the interference, reroute the speaker wiring or cable if the issue is solved. Use adhesive tape or plastic clips to secure the new wiring position.
Tips of suppressing radio interference
- The car’s metal body acts as a screen between the aerial, ignition, and charging points. Keep the bonnet closed because of this. It’ll be easier to check the interference for you.
- If a car is made with glass fiber bodies, it will be very hard to suppress the interference as a glass fiber body would have no screening effect.
- For cars with glass fiber bodywork, you’ve to line the underside of the bonnet with a conductive graphite paint or metal foil to help fit suppressors and earth-bound straps. This will make it easier to suppress radio interferences.
Fitting the aerial
The position of the aerial mast (mast is where the aerial is mounted) and the lead direction and route help a lot in successfully achieving a reception free of all interferences.
Position and fix the aerial as far as possible from the engine. If you have no other choice but to put it near the engine, choose a position for the aerial that is far from the ignition system. If you’re still unsure where to put it, you can ask a radio fitter specialist.
Make sure the lead doesn’t go through the engine compartment because it will cause interference. Furthermore, keep it far away from any electrical components and wiring.
The lead should be short so that it can collect only a few electrical emissions. An aerial hole is 19-22 mm commonly. Check that the aerial is earthed. Tune the radio to a station with a weak signal and hold the aerial firmly while you’re out of the car. If the radio suddenly gets louder upon doing this, the earthing may be the issue.
To rectify, you’ll have to take out the mounting. The mounting usually has spikes or serrations that penetrate the car’s body. Use abrasive paper to clean the metal at the contact points. Put it back together and tighten.
Suppressing a dynamo or alternator
A dynamo or alternator can be suppressed by fitting a 3 mfd capacitor for an alternator and 1-3 mfd capacitor for a dynamo. Mfd is microfarad. Attach the lead of the capacitor to the output terminal of the alternator dynamo. You’ve to take out the rear cover to reach the terminal for an alternator. Check the user manual if you don’t know how to test an alternator and for other details. The user manual will also help you to check output of a dynamo if it’s needed.
Remove the broken bolt and clean the area around it with an emery cloth to maintain a good earth. Slip the capacitor forked mounting tag below the bolt. Proceed to retighten it. If the charging circuit causes interference again, then attach an earth-bounding strap between the chassis and casing.
Finding any other sources
Interference can also be caused by any metal part of the car protected by the main body. The boot lid, bonnet, bumpers, and suspension are some of the common sources. Some electronic devices can cause interference. Auxiliary audio sources such as a satellite or iPod can sometimes cause interference too. If it’s an auxiliary device then to suppress the interference, a ground loop isolator will help.