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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;

  • High Voltage Power Line Interference - Very common
  • Thermostats and other power control circuits - reasonably common
  • Other electronic equipment (VCR, Computer etc)- reasonably common
  • Series motors and other small hand tools - not common
  • Radiocommunications (Amateurs, CB, broadcast, two way, TV stations) - not common
  • Pay TV cable leakage (signal egress) - not common
  • Radio Frequency heating equipment - not common
  • Other more exotic sources

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 Antenna Technicians Association.

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.

AMPLIFIERS. Mast head or Distribution types. There are considerations that need to be considered when deciding what sort to select. It's probably best to leave it to an expert (me) to make that selection. Its no good feeding a tiny, tiny signal into an amp and expecting all your problems to evaporate. Amplifiers are not intelligent, they amplify everything equally - desired signal, noise, interference, everything. If you have very weak signal, it would be better to upgrade the aerial and cable distribution before considering whether an Amplifier will be of any benefit to you or not.

Final note. Don't do it yourself. The additional cost of a professional installation is more than offset by the savings in blood pressure tablets alone. Find a member of the Association to do the job for you. There's nothing worse than paying the same amount of money to an incompetent monkey as a committed professional and finding out 6 weeks later that the coach screws he used were too small and he's gone out of business, or worse, he drops the aerial on your nice new shiny Jag in the driveway.  Insurance? What Insurance?  Members of the Association carry a minimum of $5,000,000.00 and are in the industry for the long haul.  If you need them, they will be there.

Digital Television is coming. Don't get conned that your current set, or the one your about to buy is Analog/Digital compatible. As far as we can determine, there are no digital sets in the Country.  In fact, they're still arguing about the Audio standard we will transmit, so there's nobody even tooling up to produce something for us yet. Don't be conned into buying a special "Digital Aerial" either. In most cases, your existing Antenna will perform adequately.  There may be problems in individual situations, especially when it comes to receiving the Melbourne ABC digital signal.

Broadcaster Current Channel Proposed Digital Channel
ABC 2 12
HSV 7 6
GTV 9 8
ATV 10 11
SBS 28 29

The table above indicates the ABC will transmit on channel 12.  Most of our current antennas are designed to work up to channel 10 only.  They will probably function sufficiently well for channel 11 (ATV digital), whether they continue to work on channel 12 - time will tell.  There are some manufacturers who have bitten the bullet and started to redesign their range of antennas to include all of the bandwidth that will be used for Analog and Digital broadcasts.  If you are just commencing to have an antenna installed, one of those may be better than the old cheap and nasty one that the current bloke is planning to stick up for you.  Ask what he intends to install and its bandwidth.  Look for the specifications on the packaging material.  If you want it to provide both Analogue and Digital signals, it has to have a bandwidth from 2 to 12 for Melbourne use.

Other difficulties which will hit digital TV will be current installations where careless installations of Amplifiers (boosters) result in poor Carrier to Noise ratios.  Additionally, all amplifiers will have to be de-rated to handle the extra power coming down the antenna lead in cable.  If the Amplifier was just barely coping before, digital will, in all likelihood, push it over the edge.  Finally, adjacent channel problems and "intermodulation" products may start to cause serious problems for the cheaper installations.  If your having an installation done now, ask the installer if the Amp he is using will cope with the changes ahead.  Insist on a straight answer.

Digital training for antenna installers is commencing, but if the person you're looking at installing an aerial claims to be "Digital Approved" or similar, look carefully - approved by who, for what.  Installations I currently do are to the best of my knowledge, suitable for the reception of Digital signals. I use quality cable and every distribution component is connected with the use of "F" connectors. I consider the effect of digital signals on every job I do, trying to anticipate problems that are coming.  I recommend a quick browse of the ABA, Standards Australia Digital Broadcasting Australia, Digital Television Group or the CAI websites to get a feel of Digital Television and the installation of suitable distribution components to accommodate it.  You might like to check out the links page at the ATA site for a more comprehensive list of appropriate links.  The Antenna Technicians Association is currently negotiating to develop a suitable training course, based on real needs and existing circumstances. A suitably qualified ATA member is going to be your best bet in the future.

Stay tuned, either here, or the ATA site for Digital updates and the effects on aerial installations.

CABLE. Many people will think nothing of spending a huge sum of money on an aerial, and because they have overspent the budget there, they scrimp in the purchase of the cable. WRONG. The excellent aerial signal you just got off the beaut aerial has attenuated before it gets to the TV set or else there are structural flaws which reduce the clarity of the picture. I use RG6 cable exclusively. Wherever possible, I use "F" connectors and compatible signal distribution equipment. The cable I use is dual screened 60% or 75% copper braid and 100% aluminium foil bonded to a solid dielectric -Belden or Times Fibre type.

IF YOU'RE THINKING OF PURCHASING NEW VCR OR OTHER ANCILLARY DEVICES, CHECK THAT IT WILL WORK ANYWHERE OVER THE UHF BAND, SO THAT YOU CAN FIND A CLEAR SPOT TO USE IT.

When digital transmissions start in Ballarat, there will be another 5 channels coming into use, crowding these VCR's just a little bit more.  So Plan ahead get one that covers the hole uhf band.

Have you considered a member of the Antenna Technicians Association?

To professionally install or repair your television antenna system?

 The member will, prior to the start of the installation carry out a

FIELD STRENGTH SURVEY

With the aid of a field strength meter (not a portable television).

This will determine the following:

     Location of the antenna (the existing antenna mast/position may not be the best location)

     Height and direction of the antenna on the mast

     Type of antenna required (combination, phased array, yagi and channels to be received)

     Available signal strength (a television requires 60 to 75 dB for clear picture reproduction)

• This allows the technician to determine if an amplifier is required, what type (masthead or distribution) and the level of gain. SO dB signal strength or less means a snowy picture.

ATA MEMBERS USE:

     The Technical Standards as laid down„by the Antenna Technicians Association Inc.

Isolated wall outlets or sockets. This helps to prevent possible electrocution from faulty televisions. (Outlets connected to low voltage line powered equipment may prevent this)

RG59 / 6 / 11 twin screened coaxial cable. (Single screen air spaced cable has greater signal loss at higher frequencies‑UHF, with less resistance to electrical and other interference)

You may also request the technician to demonstrate to you, the expected picture quality on a test television prior to giving your approval for the installation. On completion, the ATA member will record the signal strength of each individual channel and the picture quality on your invoice. 

Whilst members will guarantee their own workmanship and materials used for a specific period, no guarantee can be made or given regarding the reception quality. There are several external factors beyond the control of the technician, which can and do affect the quality of the finished installation, some of which include, but are not limited to the following;

     distance signal must travel (from point of transmission)

     objects in the signal path (trees, buildings, hills)

     seasonal changes (co channel interference, deciduous trees, sunspot activity)

     atmospheric conditions

     signal reflections (ghosting)

     quality of the signal source (relay translator)

     external interference (power line, radio transmitter, domestic appliances, etc)

IMPORTANCE OF VIDEO MAINTENANCE AND FACTORS CAUSING HEADWEAR

TO ALL VIDEO RECORDER OWNER

This suggestion sheet will help you to maintain your Video recorder in good working order, and if the suggestions are carried out, will reduce wear resulting in a longer period of good viewing.

IMPORTANCE OF VIDEO MAINTENANCE AND FACTORS CAUSING HEADWEAR

The four main enemies of your Video Recorder are: Dust, Poorly Manufactured Tapes, Excessive Heat and Dampness.

DUST

Dust can get between the tape and video heads and cause scouring. Excessive scouring of the video heads results in the appearance of horizontal lines on your television screen.

Place your video in a position free from dust and always store video tapes in their cases away from the dusty atmosphere.

POORLY MANUFACTURED TAPE

There are a number of blank video tapes for sale on the market today. Many poorer quality tapes shed the oxide layer which in turn causes damage to the video heads.

Using worn tapes should be avoided as they introduce unnecessary wear to com­ponents and they lessen the life of your video heads.

EXCESSIVE HEAT

Ensure your video recorder is kept in an area where heat build up cannot occur. Adequate ventilation is important

DAMPNESS

Although most video recorders today are equipped with DEW devices, so they will not operate under damp conditions, you should ensure that your video recorder and video tapes are kept away from humid or damp areas.

CLEANING TAPES

The use of most "dry" cleaning cassettes, particularly if they are used too often is not recommended. These products can never do the job as well as a trained technician and can instead create additional headwear, reducing the life of your video heads.

MAINTENANCE

We suggest you have your Video cleaned professionally once a year, as lack of main­tenance can lead to excessive head wear and premature head replacement. Replacement of heads is costly.

Question:     Why am I told to buy only reputable brand name tapes?

Answer:    To be sure damage wilt not occur to the video as a result of using poorly manufactured video tapes. Cheaper tapes made from less reliable com­pounds will shed the oxide layer inside your machine and reduce video head life.

Question:     What should I do when first using a new tape?

Answer:        A wise practice with new tapes is to run them in the 'fast forward' and then 'rewind' mode once before use. This adjusts the tension in a cassette.

 Question:     How should I store tapes?

 Answer:         Store all cassettes in their sleeve, making sure that the tape edge is away from the opening. This prevents dust getting into the video cassette.

Store tapes vertically and fully rewound, as this will reduce the chance of the tape sticking to the wall of the case, causing damage to the tape ends.

 Question:      Can I splice a video tape?

 Answer:        Do not attempt to do this. Even a slightly wrong join can cause damage to your video heads, seek the advice of your service agent.

FOR YOUR PROTECTION DEAL WITH A MEMBER OF T.E.S.A.  

PRESENTED WITH COMPLIMENTS BY TES.A.                        FROM:                       

RICHARD WATERS ELECTRONICS