Power Line Noise on HF: How to Find the Source and Get It Fixed
You turn on the radio, the band is full of signals, and underneath them there is a rough, buzzing hiss that you cannot get rid of. It rises and falls with the weather, it is worse on the lower bands and it seems to come from everywhere. Many amateurs live with this for years and conclude that their station is simply in a noisy location. In a large number of cases the cause is power line noise: a small electrical arc at a faulty insulator, a loose clamp or a damaged piece of hardware on a pole, sometimes hundreds of metres from your house. The problem can be solved, and it is solved by the people who own the line, but only if you can show them where it is. This guide explains how to recognise this kind of noise, how to find its source with simple equipment and how to report it in a way that gets a result.
What Creates the Noise
An electric power line carries a high voltage, and any small gap in the metal or poor contact on the hardware can allow a spark to jump. The spark is a tiny arc, and an arc produces a broad burst of radio frequency energy with each cycle of the mains. Typical causes are a cracked or contaminated insulator, a loose bolt or a clamp that has corroded, a tree branch that rubs against the wire, a metal tie wire that has worked loose and a faulty transformer or lightning arrester. The Wikipedia article on electromagnetic interference describes how arcs and sparks act as broadband sources, and the same principle applies in a power line as in a faulty fluorescent lamp.
The power is small, so why is the effect so great? Because a power line is a very long antenna. The wires run for kilometres, they carry the noise along with the current and they radiate it over a large area. A faulty pole 300 metres away can produce a noise stronger than a source that is much closer but not connected to a line. The noise is also impulsive, which means that it consists of many short pulses, and an impulsive noise looks louder to a narrow receiver than the equivalent average power would suggest.
Recognising the Signature
Not every noise is a power line problem, and it helps to know the typical signs before you start a search. Our general article on finding and killing RF noise in a modern home covers the sources inside the house, and the table below gives the signs that point to the outdoor wires.
| Observation | Points to power line noise | Points to something else |
|---|---|---|
| Sound | Buzzing, frying or rasping at 100 or 120 pulses a second | Steady hiss or birdies at fixed frequencies suggest switching supplies |
| Frequency | Strongest on 160 to 40 meters and weaker on higher bands | Noise equally strong at 28 MHz often comes from local electronics |
| Weather | Changes with humidity, fog, rain or wind | Constant noise is more often a device in a building |
| Time of day | Worse in the morning dew or after rain, may vanish when it is dry | Evening-only noise suggests lighting and consumer devices |
| Main breaker test | Does not change when you switch off your own house | Disappears when you cut the power to the house |
The last row gives the first test. Run the receiver on batteries, switch off the main breaker of your home and listen. If the noise stays, the source is outside. If it disappears, you have a problem in the house, and the next step is the one in our guide to the home noise hunt. If it is outside, the next task is to find where it comes from.
Tools for the Hunt
You do not need expensive equipment. The most useful tool is a portable AM receiver, such as a small battery radio with a loop antenna in the medium wave band. The noise from an arc is broadband, so it appears on the broadcast band as well as on your amateur frequencies, and the portable set has a directional ferrite rod that shows the bearing of the strongest signal when you rotate it. Tune the radio between stations, around 1 MHz, and listen for the buzz. A second helpful tool is a small directional antenna with a receiver for VHF or UHF, because at higher frequencies the noise is more local and a small Yagi can point at the pole. A third tool is a probe with an ultrasonic receiver, which can detect the hiss of arcing at a distance of several metres when you stand beneath the faulty insulator.
A short wave receiver with an S meter, or your normal transceiver with a battery supply, helps you to compare the strength at different points. The panadapter described in our guide to the spectrum scope and waterfall shows the comb of lines that the noise creates every 100 or 120 Hz, which can serve as a fingerprint of a power line source. If you record the sound, you can play it to the utility technician.
Narrowing It Down Step by Step
A systematic approach saves time. Begin at home and work outward.
- Confirm that the noise is outside. Use the main breaker test with a battery radio.
- Walk around the house. The meter, the service drop and the pole nearest to the house are the first suspects, because they are the closest line sections.
- Take bearings. With the portable AM radio, stand in several places along the street and note the direction in which the noise is strongest. The point where the bearings cross is the area of the source.
- Drive along the line. A car radio with a whip antenna is a good detector. Drive slowly along the road that follows the line and watch the noise level. It will rise as you approach the faulty pole and fall again after you pass.
- Pinpoint the pole. When you are within a hundred metres or so, walk and use the directional antenna, then the ultrasonic probe, close to the pole. The noise is often loudest in front of one particular pole, and it may be strongest on the side of the pole that faces the wire.
- Note the pole number. Most poles carry an identification tag or a number plate. Write it down or photograph it, with the nearest address.
Do not climb a pole, touch any wire or approach a fallen conductor. Electric lines are dangerous even when they seem quiet, and the work on them belongs to the people who are trained and authorised for it. Keep a safe distance and use your ears and a radio only.
Getting the Utility to Act
The way in which you report the problem makes a big difference. A message that says “my radio is noisy” is easily lost. A report that gives the pole number, the location, the frequencies affected, the pattern of the noise and a recording gets the attention of an engineer. Describe the evidence in a short and factual way: the noise began on a given date, it is worst in damp weather, it is present on the broadcast band and the HF bands, it comes from the pole with a given number, and you have measured it with a given receiver. Offer to meet a technician at the site with your receiver, because the technician may have an ultrasonic or a radio locator, and a person who can show the pole saves the crew hours of searching.
The legal position differs from country to country, and you should check your own rules. In many countries the owner of a power line is responsible for keeping it from causing harmful interference, and the national regulator can require a repair if a complaint is made and the cause is shown. The American Radio Relay League has collected practical advice for amateurs in its pages on radio frequency interference, including the way in which an interference complaint is made, and the information on those pages is a good starting point even for amateurs outside the United States. In Europe the products and the installations are covered by the rules on electromagnetic compatibility, and the national communications regulator is the authority for a complaint. If the utility does not respond, a written complaint to the regulator, with your documented evidence, is the next step.
Protecting Your Receiver While You Wait
Repairs can take weeks or months, and in the meantime you can reduce the effect of the noise. The noise blanker of a modern receiver is designed for impulsive interference, and it can remove a large part of a power line buzz when it is adjusted correctly, as we describe in our article on noise blankers and noise reduction. The blanker works best with a wide filter, and the digital noise reduction works better for the steady component. A directional receiving antenna, especially a loop or a Beverage that can be turned away from the source, improves the signal to noise ratio on the low bands, as we show in the piece on low band receive antennas. Moving the transmitting antenna farther from the lines and the house wiring and using a good common-mode choke on the feedline also helps, because it stops the noise from entering through the cable.
A Typical Case From Start to Finish
Consider an operator who hears a rough buzz on 80 and 40 meters every morning after a damp night. The main breaker test shows that the noise stays when the house is dark, so the source is outside. A battery radio on the medium wave band, held in the garden, points down the street to the north. A short drive along that road with the car radio shows the level rising for about 400 metres and peaking near a corner, where it falls again. Walking the last stretch with a small VHF Yagi, the operator finds that the noise is strongest below one pole, photographs the number plate and records thirty seconds of the sound. The report to the utility contains the pole number, the photograph, the recording and the times of the worst noise. A crew replaces a cracked insulator a few weeks later, and the buzz disappears. The steps are simple, and every one of them can be done by an amateur with ordinary equipment and a little patience.
What Not to Do
A few habits can make the work harder. Do not confront the neighbours before you have tested the main breaker and the house, because the cause may be a device inside your own home. Do not assume that a pole with visible damage is the source; a faulty insulator on a pole nearby may be quiet while the one with the arc looks normal from the street. Do not use a transmitter near the suspected equipment and do not take any action that could interfere with the line. Do not give up after the first complaint, because faults are often intermittent, and the technician may find nothing on a dry day. Ask for a repeat visit in the weather when the noise is at its worst, and bring the recording of the noise.
The Bottom Line
Power line noise is an impulsive, buzzing interference that is strongest on the lower HF bands, changes with the weather and stays when you switch off your own house. It is produced by small arcs at faulty insulators, clamps and hardware on the poles, and the long wires radiate it over a wide area. Use a battery AM radio to take bearings, drive along the line, pinpoint the pole with a directional antenna or an ultrasonic probe, and photograph the pole number. Report the fault with facts and a recording to the utility, and to the regulator if needed, and use the noise blanker and a directional receiving antenna until it is repaired. Never touch the line or climb a pole.
Frequently Asked Questions
How can I tell that the noise comes from a power line?
It is a rasping or buzzing noise at twice the mains frequency, it is strongest on the lower bands, it changes with the weather, and it does not stop when you switch off the main breaker of your house.
What equipment do I need to find the source?
A battery-powered AM radio, a car radio and a small directional antenna are usually enough. An ultrasonic probe helps to find the exact pole, but it is not necessary for the first steps.
Why is the noise worse when it is damp?
Moisture and dirt on a damaged insulator create a path for the spark. In dry weather the arc may stop, which is why many faults are intermittent and why the hunt is easier on a damp morning.
Who is responsible for fixing power line noise?
The owner of the line, usually the electricity distribution company, is responsible for repairs. Check the rules in your country, and use the national regulator if the owner does not respond.
Can a noise blanker remove it?
A blanker can reduce impulsive noise considerably, but it does not cure the source. Use it as a temporary measure while the repair is arranged.
Is it safe to search near power lines?
Searching with a radio from the ground and from the road is safe if you keep a safe distance. Never touch a wire, a fallen line or equipment on a pole, and never climb a pole.