Public Information Brochure 9A (PIB 9A)

Television and Radio Interference -Your guide to better reception

This information may assist householders to identify and resolve radio and television reception

problems. If, after acting on the information provided below, reception problems persist, we suggest you seek further assistance from a local service technician. If interference is confirmed, an investigation can be requested by completing and returning the PIB9A questionnaire.

Examples of broadcast reception problems

Aerials

Aerials which are designed for outdoor use and properly positioned outside the house usually help television receivers to resist interference by amplifying the wanted signal. Generally, indoor aerials do not work as effectively as outdoor aerials, and are more likely to pick up electrical interference. Indoor aerials may be satisfactory in strong signal areas, but when an interference problem occurs it is usually necessary to install an outside aerial. With outside aerials, factors which can influence the quality of television reception include the type of aerial, its mounting position, and the condition of the aerial and aerial lead. RSM will not investigate television interference resulting from use of an indoor aerial.

Most of these points also apply to FM radio receivers. Portable FM radio receivers are usually fitted with a telescopic aerial, the length or position of which can be adjusted for improved reception. Best reception is usually obtained with an outdoor aerial. AM radio receivers are usually fitted with a built-in directional aerial. Some have a socket for an outdoor aerial, such as a long wire or large vertical whip, for improved reception. If no socket is available, a service technician should be able to modify your receiver for connection to an outdoor aerial.

Weak signals

It is usually impossible to cure interference to the reception of distant broadcast stations that are not intended to cover your location. Each television and radio broadcast station is designed to service a particular geographic region, called its coverage area, within which there should be sufficient signal strength to override the background level of interference that is usually present.

Television:

Weak signal reception looks “snowy.” Where the signal level is being reduced by an obstruction, it may be possible to find a new location for the aerial on your property where the signals are not blocked. Often, a higher performance aerial will help overcome problems caused by low signal strengths. Sometimes, a mast-head amplifier may be necessary, although such an amplifier may increase the level of local interference as well as the desired signal.

What you can do

Check your aerial system for loose or corroded connections, or damaged cabling. You may need to contact a service technician or aerial specialist for assistance to do this.

Radio:

AM radio reception of weak and/or distant stations at night is prone to fading and distortion, caused by the simultaneous reception of both wanted and unwanted signals.

What you can do

Check your aerial system or re-orientate your radio. If there is no improvement, contact a service technician or aerial specialist for further assistance.

Ghosting

The multiple television images seen in this picture are produced when part of the signal comes directly from the transmitter, while another part has been reflected from a hill, a building or some other large object in the locality. FM radio reception may also be affected by multi-path reception. A common symptom of this problem is a harsh edge to the sound, often accompanied by the stereo light flashing. It may also cause a flutter effect on car radio FM reception when the vehicle is moving.

What you can do

Better picture or sound quality can sometimes be obtained by altering the alignment of the aerial. This will require someone to watch or listen for the best reception whilst the aerial is slowly pointed from side to side, up or down, or twisted. If that is unsuccessful, it is usually possible to find another position for the aerial which results in better reception. Where the problem persists, ask an aerial specialist if there is another type of aerial available which may be more suitable for reception in your area.

Co-channel interference

The effect shown here is caused by two pictures being received at the same time from two different television stations operating from different locations, but sharing the same television frequency. This type of interference can sometimes occur because there are many hundreds of different television transmitters at hundreds of locations around the country, and they have to share the 11 VHF and 36 UHF channels that are available. For example, VHF channel 3 is used for TV2 in the coastal Taranaki area but is also used for TV1 in the Nelson area. Under certain weather conditions strong signals can be received from distant transmitters operating on or near the same frequency as your local station.

What you can do

Annoying as it is, this sometimes severe condition is usually infrequent and temporary, ceasing as suddenly as it began. There may be no practical solution. If this interference is frequent and severe, an aerial specialist can advise you as to whether a different aerial would help.

Electrical interference – power lines

Television:

The interference pattern shown on this picture may be caused by a nearby high voltage power line. Weather conditions are often a factor in this type of interference, which may be continuous, or come and go during windy weather, and may cease after rain.

Radio:

AM reception is more prone to power line interference than FM reception. The interference is characteristically heard as a buzzing noise.

What you can do

If this is found to be the cause of your TV or radio reception problems, we recommend you report this to your power company.

Electrical interference – household appliances

Television:

Television interference can often be caused by domestic electrical appliances, either in your own home or in that of a near neighbour. It is commonly caused by faulty or non-compliance switch mode power supplies in appliances such as computers, DVD players/recorders, digital receivers, compact fluorescent lighting and some plug packs. Typically the effect is dotted diagonal lines that appear on the screen. Interference may occur when the device is switched on and/or when it is on standby. Noting the times when interference occurs will help you with its identification. This is particularly relevant for thermostat controlled appliances such as fridges or heaters. The interference pattern in this case will typically be one or more horizontal bands of flecks.

Radio:

AM reception is more prone to appliance interference than FM reception. Typical sources are similar to those affecting television.

Other causes of interference

Wireless devices (cordless phones, baby minders etc) operating on incorrect frequencies also cause problems. Other potential causes of interference include masthead preamplifiers, TV distribution amplifiers, electronically controlled washing machines, and motor speed controls.

What you can do

Check your receiver and aerial. A faulty outdoor aerial, a break in your aerial lead, or the use of an indoor aerial may cause your receiver to pick up background electrical noise normally swamped by the broadcast signal. Check for potential sources in your own home. This can be done by turning off all electrical products in the house, one by one (while the interference is occurring), until you find one that stops the interference. Ask your neighbours if they have the same problem. If they do, interference is the likely cause. However, be sure that they get exactly the same problem at the same time on the same station, or their answer may be misleading. Preferably, check the problem yourself on their receiver. If a neighbour’s appliance appears to be causing interference, keep in mind that even if they are also receiving the interference they may be quite unaware of the cause. Be reasonable in any approach you may make. If you are unable to identify or locate the source of the interference, contact your local service technician in the first instance.