Radio interference

We occasionally get phone calls from people who after fitting their reversing system end up with interference on their radios. As the system is the last item fitted the blame is often attributed to it. However the situation is usually a lot more complex than that and finding the source of the issue can prove difficult. In our experience it almost always occurs it is on vehicles with aerials that run along the front windscreen. This points more to an issue around the aerial which is disturbed by the new wiring installed.

Types of noise:-

Backway noise:- This is noise that arrives via the power or ground wires to the receiver. If the noise is only there when the engine is running and increases with the engine then this is alternator noise. Fitting filters to the alternator and power line to the radio can cure. As the noise was not there before the reversing system was installed then there are several possibilities. Newly laid cables may be picking up interference from adjacent cables. Moving them can obviously help cure the issue.  The choice of where you have connected the power line may be unsuitable. For example if you have ignored our instruction never to connect direct to a battery. One reason we advise that is it can be a source of interference. Interference can also arrive via the ground cables. With earth connections avoid using the same earthing point as the radio.  Also check the car radio has a good earth point.

Noise from the aerial:- You will get this noise with or without the engine being on. When you have the reversing monitor on the noise will be there and when it is off the noise goes. You might notice the noise varies as you move your hands around near the monitor. Experience suggests this is a problem with the aerial especially if it is mounted on the front windscreen. FM aerials work best if they are vertical in the middle of a horizontal ground plane. If it is mounted across the windscreen then this is far from ideal. These are usually amplified as well which amplifies the problems! Placing a monitor close to the aerial will influence the efficiency of the aerial as it is a metal object which will affect the ground plane of the aerial. Trying a more substantial aerial in the ideal position on top of the vehicle should cure. In many vehicles this is not an option so locating the monitor as far away from the aerial will improve the noise. The clip on mirror monitor is most likely to cause this issue and replacing with a stand on dash style usually cures it.

Sideway noise:- This is noise that arrives from a nearby noise producer. As the monitor was the last item fitted then there is potential there. Modern monitors use LED backlights which are low voltage. If the monitor is emitting noise then hold another radio close to it should identify if it is the cause. It is best to have it tuned to a frequency not containing a radio channel. The noise is also likely to be present if you are playing a CD on the radio. In the past monitors with compact fluorescent tubes as back lights were prone to giving off interference as they had high voltage power inverters. The most likely source of interference from a modern monitor is the voltage regulator chip. These operate on a switch mode basis which effectively maintains a constant voltage by rapidly turning on and off. This is usually found internally in the monitor or in a small box on the power lead. If you have the box type, try moving it away from any wiring related to the radio – especially the aerial. You can also buy filters that eliminate noise picked up by an aerial.

New wiring can carry noise from a noise source from some distance away. Sometimes disconnecting the camera cables stops the noise which suggests they are picking it up from somewhere along the cable run. Re-routing the video cables can help in this situation. This can be very true on modern vehicles where data cables and pulsed voltage cables to CANBUS modules can be a source of interference to cables running alongside. We have found that if the interference looks to be caused by the long extension to the camera ferrite cores fitted front and back can cure it. On some of our monitors there is no filter box on the power lead and a rectifier fitted on the power cable where it is attached to the vehicle electrics has solved the issue (caused by the interference running along the cable from another source - in the one case a dashcam).

In the past we have come across monitors where the fault lay in the power board being the source. Changing that has cured the problem. We usually find though it is an aerial issue or someone has taken power off a source not controlled by the ignition. We can offer advice and give practical assistance to a degree.

Interference is rare, but it can happen. We advise you test out your system with the cables roughly in place. If all is OK then you can then fully install them. If all is not well you have the chance to easily re-route the cables.

Questions we will ask:

Where have you taken the positive feed?

Where is your aerial?

Is the interference there with the engine off?

Is the interference there with the cameras disconnected?

When you hold a different radio close to the monitor and power box do you get interference?

Does it give interference when playing a CD?

Does the interference reduce as you move the monitor away from the radio/aerial?