Although the problem has been around since the dawn of radio communications and broadcasting, power-line noise issues are A on the rise. The proliferation of electrical, electronic, mobile and wireless devices — which are susceptible to power-line noise — have contributed to this increase. The law requires utilities to rectify power-line interference, but this does not have to be a budget-breaking experience. By using proper approaches, utilities find that dealing with a power-line noise complaint is seldom time consuming or expensive.

Power-line noise can interfere with radio communications and broadcasting. Essentially, the power lines or associated hardware generate unwanted radio signals that override or compete with desired radio signals. Power-line noise can impact radio and TV reception, including cable TV head-end pick-up and Internet service. Disruption of radio communications, such as amateur radio, can also occur. Loss of critical communications, such as police, fire, military and other similar users of the radio spectrum, can result in even more serious consequences.

Sparking or arcing across power-line related hardware causes virtually all power-line noise that originates from utility equipment. A breakdown and ionization of air occurs, which results in a current flow between two conductors in a gap. The gap may be caused by broken, improperly installed or loose hardware, which causes inadequate hardware spacing, such as the gap between a ground wire and staple.

There are obvious reasons why utilities should be concerned and aware of potential issues. To begin, interference impacts quality of life. It's a matter of good customer service to be diligent in responding to customer complaints. In addition, arguing or avoiding customers can be time consuming and may lead to litigation. Next, it's in a utility's best interest to act immediately, because most power-line noise is caused by arcing conditions, which can lead to utility equipment or material failures. Last, interference issues must be addressed. FCC regulations require utilities not to cause harmful interference to licensed services and to cease operating any device, upon notification by the FCC, that is causing interference.

FCC Part-15 regulations govern radio and TV noise most likely to come from utility-owned equipment. These rules specify three classes of emitters that may apply to power-company equipment:

• Incidental emitters

  Most interference complaints from power-company equipment result from an incidental emitter, such as an electric motor or sparking power-line hardware. Incidental emitters don't intentionally generate radio energy but do so incidentally as a result of their operation.

• Unintentional emitters

  These may be found in some power-company equipment. Unintentional emitters intentionally generate an internal radio signal, but do not intentionally radiate or transmit it. Examples include some types of “switch-mode” power supplies and microprocessors used in some power-company equipment. Unintentional emitters have specific limits on radiated and conducted emissions.

• Intentional emitters

  These are transmitters that intentionally radiate RF. In general, they are not found in power company equipment, although some remote-reading usage meters may use intentional emitters.

Most radio noise on power-company equipment comes from incidental emitters. These have no specific limits on conducted or radiated emissions. But all unlicensed emitters of radio energy have a requirement not to cause harmful interference. If they do, the operator of the device causing the interference must take whatever steps are necessary to correct it.

Keep in mind, electric utilities are responsible for correcting only the noise generated by the equipment and hardware that they actually own. In cases where utility customers use an appliance or device that generates noise, they must correct the problem, even if the noise is conducted and radiated by the utility's power line.

A good first step is to eliminate the device itself as the source of the problem. If the device is suspect, remove the antenna connection to the radio to see whether the noise goes away. Proceed with the following steps to determine if the source of interference is located within the home or business.

1. Go to the main breaker panel or fuse box. Check the presence of the noise with a battery-powered radio.

2. If the noise is present, shut off all power to the premises by turning off the MAIN circuit breaker or by pulling the MAIN fuses or meter. If the noise on the AM radio stops while the power is off, the source of the interference is within the residence. If the noise continues, you can assume it is coming from a point external to the customer's home.

3. Restore the main circuit breaker or fuses or meter.

4. If the noise stopped while the power was off, locate the circuit supplying the power to the noise source using an AM radio as before, and de-energize the individual circuit breakers one at a time until the noise stops.

5. Next, determine what is on the circuit by going from room to room to isolate outlets, appliances and lights until the offending device is found.

If the noise source is not in the customer's home, check with the closest neighbors. If one of the neighbors has a similar problem, ask them to run the breaker test to try to locate the faulty equipment. A household appliance or electrical device rarely causes interference that extends beyond a few houses on a secondary system.

Note that if the source is not in the customer's home or a neighbor's home, the noise is originating from an outside source. Direction-finding techniques may then be used to isolate the noise to a particular residence or an area of the utility's power-line system.

Noise that varies with the time of day is related to what people are doing, usually pointing to an electrical device or appliance. Noise from consumer-type devices often comes and goes with periods of human activity, frequently correlating with evenings and weekends. Unless it is associated with climate control or an HVAC system, an indoor RFI source is less likely to be affected by weather than power-line noise. The importance of maintaining a good and accurate interference log cannot be overstated. Ask the customer to record dates, times and weather conditions. Correlating the presence of the noise with periods of human activity and/or weather often provides important clues to identifying power-line noise.

If the interference appears and varies in intensity depending on weather conditions, and if a breaker test excludes sources inside the home, the interference may be caused by faulty components associated with the electrical power lines near the home. Wet weather may temporarily reduce or eliminate the noise by shorting out spark gaps on the power line. Windy weather may cause the noise to vary or even stop for a while, as loose hardware is affected.

Virtually all radio noise originating from utility-company equipment is caused by a spark or arcing. The radio noise is only generated during the times when a breakdown and ionization of air occurs.

Once an ionized path is established in the gap, current flows at all parts of the cycle where the voltage is higher than the breakdown voltage of the gap. This typically occurs only near the positive and negative voltage peaks, the times of highest instantaneous voltage. Sometimes the gap may break down on only one polarity of the waveform.

Because power lines carry 60-Hz ac, the voltage on them passes through two peaks each cycle (one positive and one negative) and passes through zero twice each cycle. This gives 120 peaks and 120 zero crossings in each second. Power-line noise follows this pattern, generally occurring in bursts at a rate of 120 (sometimes 60) bursts per second. This gives power-line noise a characteristic sound that is often described as a harsh and raspy hum or buzz. Because the peaks can occur twice per cycle, true power-line noise usually has a strong 120-Hz modulation.

Typically, power-line noise is a broadband type of noise starting at the low end of the radio spectrum and is usually stronger at lower frequencies. It occurs continuously across each band, up through the spectrum to some upper frequency where it tapers off.

Indoor and power-line noise can be identified with an oscilloscope, which should show the bursts occurring every 1/120 seconds, or 8 1/3 ms. Investigate the suspect noise from a radio's audio output using the AM mode. Use the wide filter settings and tune to a frequency without a station. Power-line noise bursts should repeat every 8.33 ms. If this is not the case, you probably don't have power-line noise (Fig. 2).

Alternately, you can perform a similar test if the noise pattern is visible on a TV set. The noise occurs in two horizontal groups or bands. Typically, these two bands drift slowly upward on the screen. One group is a result of arcing during the positive half of the 60-Hz sine wave. The other group is a result from the negative half of the sine wave.

Usually, it is best to perform this test at the lower VHF TV channels and with an antenna (as opposed to a cable hookup). The positive and negative power-line noise burst also may have slightly different characteristics. This can cause each half of the cycle to have a slightly different pattern on the screen. As you turn the channel selector to higher frequency channels, the interference should diminish. If the interference can be observed on UHF channels, the source is probably relatively near (Fig. 3).

A simple step-by-step procedure handout, plus instructions for “locating inside sources” and “locating the residence” can be downloaded from www.rfiservices.com. Providing it to your complainant as a first step can reduce your on-site investigations by as much as 65%.

Once you've eliminated the possibility of an internal noise source, always start the RTVI locating process at the interference site using the customer's equipment. Whether a TV interference (TVI) or radio frequency interference (RFI) complaint, monitor the customer's equipment while the problem is active.

Attach a Defect Direction Finder (DDF) receiver to the customer's antenna (Fig. 4). This specialized equipment enables you to monitor the symptoms as received by the customer's antenna. The setup should include a broadband AM receiver that covers the frequency range affected by the problem, an oscilloscope (scope) and an attenuator or RF gain control to adjust the RF signal level. With these tools, utility personnel can monitor the sound and pattern produced by the RTVI source(s).

Scope patterns show many important facts about the source(s) affecting the customer's equipment. They can reveal the number of simultaneous sources, determine which source is the strongest, and even provide an indication as to the size of gap across which the spark is occurring. When working with TVI complaints, the scope can show which source is having the most impact on the TV picture.

Each sparking interference source exhibits a unique pattern. By comparing the characteristics between the pattern taken at the customer's residence with those found in the field, it can be determined which is the offending source because each provides its own “fingerprint” or “signature” (Fig. 5).

Interference locating receivers, such as the Radar Engineers Model 240 shown in Fig. 4, have a built-in oscilloscope display and waveform memory, providing the ability to toggle between the pattern saved at the customer's house and those obtained from sources located in the field.

Once armed with the customer's noise fingerprint, start the search in front of the customer's residence. Travel in a circular pattern around the customer's house, block-by-block, street-by-street, until you find the noise pattern matching the one recorded at the customer's house. Use VHF or UHF if you can hear the RFI at these frequencies. The longer wavelengths associated with the AM Broadcast Band (and even HF) can create misleading “hot spots” along a line when searching for a noise source.

At these frequencies, you may find that the noise peaks at certain poles with different types of hardware mounted on them. As a general rule, only use the lower frequencies when you are too far away from the source to hear the offending RFI at VHF or UHF. Work at the highest frequency on which the noise can be heard. As you approach the source, keep increasing the frequency (Fig. 6). Once you've matched the pattern obtained at the customer's house with one in the field, you're close to locating the structure containing the source.