NZART is a non-profit association of amateur radio operators
The New Zealand Association of Radio Transmitters Incorporated
Prepared by NZART Council, 2001
This is a guide for radio amateurs whose operations come to the attention of neighbours through disturbance to reception of sound broadcast and television transmissions (broadcast interference-BCI and television interference-TVI). This disturbance is a continuing risk in amateur radio, and all radio amateurs can expect to cause or to be accused of causing BCI or TVI at some time. The interference is not damaging and the accusation does not bring any disgrace.
Interference between one radio service and another is inevitable from time to time, because all services share the one radio frequency spectrum. You must face the problem only when it arises, and you should not worry about it beforehand. You should not fear a TVI or BCI report in any way or restrict your activities or hours of operation because a report may arise.
The best advice is this: ensure that the apparatus in your own home is free from interference caused by your amateur radio activities--and be active on the air. In all cases of interference, a cure is possible. Problems can be cured only as they arise. In reading this guide, which treats TVI in greater detail, bear in mind that in BCI cases you must take a similar approach.
The exact procedure to follow in interference cases cannot be laid down. Each case differs. Neighbours have been known to complain of interference after a radio amateur has erected a new aerial but before it has been used for transmitting. In other cases, neighbours have tolerated overhearing transmissions because they like to feel informed. Few hard and-fast rules can be offered.
Interference to broadcast-band receivers is often reported. The broadcast receiver cannot be considered to be of adequate design unless it has a radio-frequency amplifier stage and is connected to an outside aerial. An internal aerial or an aerial in the same room as the receiver is not to be accepted as satisfactory.
The amateur's transmissions may be able to be received at various points on the tuning dial, but the generally-accepted rule is that the case is one of interference only when reception of the local broadcast stations is disturbed.
By some reports, an amateur's transmissions are heard from record players, stereo grams, and similar audio devices that are not designed for the reception of radio transmissions.
On receiving a report of interference to such an audio device, courteously discuss the matter with the owner, and advise him to contact the supplier or his supplier's agent to arrange for it to receive attention and to have the deficiency cured. These devices are not designed to be radio receivers.
The important point to remember about TVI is that it can be cured. Bear this point in mind at all times. TVI must be challenged head-on and a cure found for each separate case. Unfortunately, there may be no easy way or shortcut.
When you start transmitting from a new neighbourhood or with a new rig, first ensure that your own television set is absolutely free from TVI. Then operate without any self-imposed restrictions of any sort. That is, operate when you want to, for as long as you wish, on any authorised band, with any power up to your legal limit, and with no disturbance to your own television receiver. A radio amateur's first operating concern should be to ensure that the television receiver in his own home is disturbance-free. It should not display any interference when operation is taking place on the frequented amateur bands.
Your television receiver is very close to the transmitter and its aerial. Having your TV receiver "clean" is important for several reasons, the first being that it promotes domestic or family harmony! Your receiver will be the subject of the first tests the MED RSM Official may want to make--and revealing a clean display on your own television set will incline him in your favour. Revealing a clean set can also help you to deal with neighbours who do not believe that the fault lies in their own installation. If your own TV set is not TVI free, therefore you should make it so.
Do not ask the neighbours for TVI reports. Let the neighbours first report the matter either to yourself or to the MED RSM. Wait for the TVI reports (if any) to come to you--they may never come.
TVI reports can come from several directions and in several ways. The neighbour may contact you or a member of your family. An MED RSM Official may contact you. The report may be very complete, may be garbled or incomplete, may be casual, or may be second or third hand. Be sure you recognise a TVI report as such, and note it well.
This depends on the nature of the TVI report reaching you, the degree of co-operation shown by the neighbours, and how well you know them. If the neighbour directs threats or abuse at you, or is not known to you, or claims that the fault is wholly yours, do not hesitate to notify the MED RSM by telephone.
You would be wise to be prepared to give a short history of any previous TVI problems you have experienced in this same location. Have you cured similar problems? This is where the notebook becomes useful.
If you do not show any TVI on your own set, continue to operate until the matter can be investigated. If your neighbour is co-operative and is prepared to let you or a friend examine the set; then offer to do some tests to try to reproduce the conditions that gave rise to the interference. You may be able to cure the problem without involving the MED RSM staff at all. Please be aware that the MED RSM may charge someone for their services. Make enquiries first to determine any costs involved and where their account is likely to be directed. This may depend on where the source of the interference is finally found.
The technical mechanism or whatever generates the interference or disturbance must be established early to determine:
The tests may or may not be conducted by the MED RSM. They could be conducted by some other competent person provided the co-operation of the neighbour is assured. Note that one or more mechanisms may be creating the interference, and so more than one cure may be necessary at any television installation. At any one transmitter site, the disturbance in adjacent television receivers may be generated by quite different mechanisms.
The two problems that arise with TVI are:
High-pass filters (at the television receiver aerial terminals) and low-pass filters (at the transmitter) do not always cure TVI problems. Substitution of other TV sets can generally show if the cause is a faulty transmitter or faulty television receiver, but if substitution shows the interference effect to continue, then the cause becomes more difficult to establish.
The "rusty-bolt" effect is one of the hardest of all these TVI causes to locate. If a known clean transmitter is causing interference to a known good television receiver, then an external cause can be suspected. Perhaps the transmitter signal is being picked up by a local conductor such as a clothes-line or fence-wire. A rusty or corroded joint in this conductor may be acting as a diode. Harmonics of the transmitter signal could be produced by this spurious diode detector and re-radiated. These harmonics can be received by the television receiver and cause interference to the picture or sound. Such interference may vary with the weather.
It may be intermittent and be affected by wind as well as rain. Typical offenders are metal- tile roofs, metal gutters and down pipes. A heavy blow with a hammer may sometimes
correct an offending joint. Applying water from a hose can sometimes change or remove the interfering source and help to identify the culprit. Either bonding or insulating the offending joint may solve the problem.
More than one joint may be causing trouble. Bonding is generally impossible with metal tiles. Shifting the television aerial away from the offending harmonic source or sources is a more practical cure. A bonded wire mesh over the offending joint may be considered. It is unlikely that a complete metal roof will have to be bonded to effect a cure.
Bonding suspect joints can sometimes produce problems. With bonded conductors, a better signal pick-up may result, larger radio frequency currents may flow, and the problem may shift to another joint that was hitherto not suspect. Insulating the suspect joints may sometimes be more effective. A change to nylon guy-wires may sometimes eliminate problem joints.
The accepted rule is that if the offending joints are on the amateur's property, the problem is his. If the offending joints are on the property of the television set's owner the problem is his, Unfortunately, few set-owners understand this problem and so the radio amateur should offer technical assistance and advice. Re-siting the television set aerial or the transmitting aerial is often the only practicable cure.
If the television set has been shown to be faulty and is under a guarantee or a service contract, then give the firm concerned early advice of the problem. This is best done after the MED RSM has been advised and the problem discussed. Advise the firm concerned that the MED RSM is aware of the problem. These actions are really the concern of the television set's owner, but the radio amateur may offer to assist.
Rental sets should be treated in the same way as a set with a service contract. A rental set has the advantage that a change to another model may be possible, which could cure an otherwise difficult problem.
As a radio amateur, you should be aware of the undesirability of agreeing to fix a neighbour's equipment. The equipment may be under guarantee, may be covered by a service contract, or may be rented. It may not belong to the person who is using it, who may not always be honest and forthright about ownership. Where to draw the line depends very much on how well you know the neighbour, and other factors, such as the age of the set, and the nature of the problem itself. Your "unauthorised tampering" may invalidate guarantees and service contracts. Future problems with the equipment -in no way related to the interference problem -will without doubt be blamed on the radio amateur. No radio amateur wants to be concerned with the maintenance of his neighbour's equipment for evermore. The possibility of double-blame must be avoided (first the interference, and then of damaging the set). Safety and Regulations are good reasons for keeping out of a neighbour's set. Many modern television receivers may operate with the chassis alive -at about half mains voltage. This also means that short lengths of coaxial cable inside the set (to the aerial isolation unit) could appear to have the outer at earth potential, but in fact this outer could be at a hazardous potential. Under the various Electrical Acts and Electrical Regulations, a radio amateur is not qualified to service mains-operated television receivers.
Slight disturbances on a television test pattern which are barely noticed by a trained eye will not be seen on a television picture. Disturbances of the same level as the noise on the picture, and less than interference from motor vehicle ignition, electrical appliance noise or aircraft flutter, are acceptable. Tearing of the picture, herringbones, or switching between colour and black and white are unacceptable. The last trace of TVI may be slight changes at the areas of intense red in a picture. This is acceptable for unless attention is drawn to it, it will be unnoticed. Noises from an adjacent transmitter should not be heard during pauses in the television sound. It is wise not to draw the attention of the owner to minor disturbances. Instead, check if he is satisfied with the quality of reception. The neighbour should be unable to tell when you are transmitting.
Where substitution of another set or other tests have shown that the fault is within a particular television receiver or other piece of commercial equipment, consider approaching the manufacturer of the equipment. When or how this should be done depends on the attitude of the local agent for the equipment, and the status of the guarantee or service contract. Ideally, the local supplier of the equipment should handle communications with the manufacturer in cases where a manufacturer's modification or the expense of a local modification arises. Again the radio amateur may offer to assist the owner. If you approach a manufacturer, be certain to include details of model type and serial numbers, age of set, installation arrangements, tests conducted and their results, and any other details that will help in an analysis of the problem, diagnosis of its cause, and the development of a cure.
The radio amateur should accept responsibility for being the cause of TVI, only if carefully conducted tests have established:
The owner or user of the television set must accept responsibility for curing the interference if carefully conducted tests show:
If a television viewer chooses to view television programmes on a defective set, or a set with a defective installation, he should not expect a radio amateur to cease transmissions to remove the disturbances to his viewing.
Be careful with the use of words. An amateur transmitter does not "interfere with" or "cause interference" to television reception until properly conducted tests have clearly established that the fault is in the transmitting equipment or the transmitting installation. A properly adjusted transmitter, radiating a "clean" signal, does not "radiate interference" or "cause interference".
Disturbances to television reception should not be described as "interference" if the television set has deficiencies in its design or installation that cause it to respond to signals from a "clean" transmitter. A faulty television receiver or installation that responds to the amateur transmitter's "clean" signal does not exhibit "interference" -although this is the term often given to it (TVI). "Reception is being disturbed" is a better description. If the transmitter is faulty and radiates energy that enters the television set at the television channel frequencies, then this is clearly a case of "interference". The amateur transmitter is then "radiating an interfering signal". If the fault is at the television receiver, and the transmitter is blameless, then the transmitter cannot be said to be "causing interference".
Be tactful when explaining to a neighbour that his television receiver or installation is faulty. An explanation such as follows is satisfactory and typical: "You have a very good set. It displays each channel very well, with good crisp pictures and pleasant sound. Unfortunately, it also responds to signals not meant for it, and this means it is defective. Other sets in the area are known to be unaffected in this way ...
By means of some tests, we can determine if the fault is inside the set, or if it can be cured by changes to your aerial, or if your installation needs a filter or trap added to the aerial lead."
The punch line "it also responds to signals not meant for it, and this means it is defective should be carefully explained. Contact with the neighbours may be by a visit, telephone, or a formal letter. The procedure to adopt depends how approachable they are, how well you know them, and where the TVI report came from, and how it was conveyed to you. There is a need to explain to the layman what Radio Frequency Interference (RFI) is, and what radio amateurs do.
The possibility of a TVI report is ever present. Once a cure has been effected to a TVI case, there is no known way of ensuring that the same set will not again become subject to TVI at some later time, perhaps by other cause. Damage and corrosion takes its toll of aerials and earthing systems. Sets age and become faulty. The radio frequency spectrum is a shared resource, and until we have new knowledge or techniques, all radio amateurs must learn to live with the possibility of a TVI case arising at any time and be trained in how to handle it when it does arise. A radio amateur should not, and can not, give a neighbour a guarantee that a TVI cure just made will remain effective for any period.
It may be found that a high-pass filter, traps, stubs or other device fitted at the aerial terminals of a neighbour's TV set will cure disturbances to his viewing. It is important to leave a label or tag securely attached to the set, which gives reason for the installation of the device -otherwise the device may be removed by someone in the absence of an interfering signal "because it has no effect"!
NZART Branch should designate a member of its Committee as Interference Officer, his duties being to receive requests for assistance on BCI / TVI matters from members. He should have power to enlist other technically qualified members of the Branch into a team to help any member who needs tests, diagnosis, negotiations, advice, and other support until the case is closed.
Amateurs should be seen to be united -this is important. An independent expert third party may be acceptable to a neighbour in difficult cases. Branches should be aware that the NZART Council is in a position to help with problem BCI / TVI cases, particularly where added technical assistance is required, or where an amateur is under pressure from a local dignitary or influential person. NZART Council has the route through the NZART Administration Liaison Officer available for official negotiations on behalf of a member if the Council deems them necessary. Difficult technical or social TVI/BCI interference problems should be notified to NZART promptly.
Remember that all BCI and TVI cases are capable of being technically cured. All you need is patience to test, diagnose the problem, and work out a cure. Many good textbook and magazine articles have been published and are available. The problem is not yours alone. Other radio amateurs are available to help you, many having experience with the problem.
The MED RSM are there to help. TVI and BCI are accepted as a part of radio life and technical progress. The neighbour also has a part to play. Cooperation and patience are necessary. Don't allow yourself to worry, and don't allow your neighbour to think that you should stop your operations.