TV INTERFERENCE

In this page, I set out a number of checks that should be carried out before blaming all and sundry for that squiggle on the ABC every Sunday night while "The Bill" is on. I also discuss a number of typical Interference sources and touch on ways to identify the source.

Firstly, MAKE SURE ITS NOT YOUR OWN FAULT.  I know of countless instances where the "interference" was simply a deficiency in the TV set, VCR or the Aerial of the customer affected.

If you have TV interference, it's worth while to call in an Aerial Technician initially to give the aerial system a thorough going over as a first step.  He may point out matters to you which should be attended to or simply point out that it looks like a crook TV or similar.  The second step is to have a TV Technician check over the equipment and give it a clean bill of health.

If both of these tradesmen agree that it is external interference, then it's time to take the next step:  What sort of Interference do I have?

The most common forms of external interference which are often found in the community are;

The first port of call is the Australian Communications Authority (sorry guys). They will provide you free advice and a booklet containing photographs of a range of interference sources.  The booklet also gives advice as to the course of action to eliminate the source.

Additionally, there are sites on TV interference on the web, much more comprehensive than this simple attempt. You might try starting with the FCC site and then browse around a bit.

What do I do if I identify the interference from the pictures in the ACA booklet "Better Television and Radio Reception"?

If you think you have nailed the source the booklet will direct you to the appropriate course to rectify your problem. For instance, if your problem is identified as Power Line Interference, the really only effective solution is to contact your Power Reticulation Company. They have the necessary wherewithal to tackle the problem. Sometimes, friends, relatives or acquaintances will tell you suburban myths about "dirty insulators" and cleaning them with a jet of water. DO NOT DO THIS -DO NOT EVEN ATTEMPT TO DO THIS. Why do you think power companies spend a lot of money on specialised high pressure pumping equipment and insulated work platforms?

If the booklet identifies your problem as a Radio transmitter, the most straightforward identification option is to go outside and look straight up in the air. Any radio transmitter close enough to cause you a serious problems will have a transmit aerial close enough for you to spot fairly readily.  The next step is to sort out what sort of radio you are dealing with and its approximate frequency of operation.  Knowing this, filters can be fitted to keep the radio signal OUT of your TV or Radio set.  In most cases, it is a deficiency in the TV or Radio which allows the interference to occur.  Keep the signal OUT and remove the problem.  Typically, a CB radio or a "High Frequency" Amateur Radio Station may require a filter on the aerial input to the TV or radio and perhaps some attention to the power line (which may be acting as an aerial for reception of the extraneous signal).  It may be appropriate to seek some assistance from a skilled technician if this becomes necessary.  Try fitting a "High Pass" filter which you will find in your local electronics sales emporium to your Television (or VCR) antenna input socket.  If the problem is caused by two way radio transmitters (as opposed to the hobby services - CB and Amateur) or perhaps caused by the Very High Frequency Amateur Radio transmitters, you need an expert straight away.  Don't waste your time with some goose who installs antennas part time out of the boot of his EH.  At the very least, consult a member of the Television Electronic Service Association (TESA) or the Antenna Technicians Association (ATA).

To identify the location of most of the junk that is radiated from domestic switching devices - thermostats, series motors, light control, faulty switches, etc, try listening for a corresponding interference with a portable radio receiver. If you can hear the corresponding rauccous noise, attend at your power distribution board with the portable radio, wait for the interference. When it commences, shut down all of the power to your house and listen for a coincidental cessation of the interference on the portable radio receiver. Did it stop?  If it did, your problem is inside the house.  If it didn't, it's elsewhere.  If it seems to be inside the house, do the same test with each individual power circuit, until you can identify a particular fuse or breaker where the problem is residing.  Individually inspect each appliance connected to that circuit.  Do not neglect power outlets which may be in the ceiling space or under the floor.  Once you can identify the appliance concerned - call the service representative to deal with the particular appliance.

There are many sources which are not covered in this page. One of the most common problems seen these days is what is called "switch mode power supply radiation". Briefly, most electronic equipment these days does not use a transformer to derive the various voltage levels which may be required in any appliance.  Instead, they use "switch mode power supplies". These can be considered as similar to a light dimmer. They accept mains voltage in and have a preset level out which they derive by "switching" on and off as needed, to only allow sufficient of the mains through to create the particular output voltage required.  In the process of switching on and off, switching transients cause small white spots to be seen on the TV screen. These spots generally are fairly evenly distributed over the screen, although sometimes they seem to clump together. They usually form fairly regular lines of spots. The lines can be either straight or curved and may swing around and vary as you watch the TV depending on the stability of the switching process. Often, people refer to these lines as "isobars" on the TV screen.   Channel 2 is the station which is most commonly affected by this form of interference - because of its frequency of operation.   If you think this is your problem, you need to isolate any electronic equipment near your TV.  The most common sources are the TV set itself, the VCR which is usually adjacent, or sometimes, where it is in use, a Pay TV decoder.  You need to bypass the aerial from each suspect device, one at a time, and then pull the power plug out of the wall for that device.  If you notice an abrupt cessation of interference, it's time to call the serviceman for that particular appliance.

I'll add more notes from time to time. If you have a specific inquiry try emailing me.

This page was last updated on Sunday, 24 April 2005 20:31

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