Noise on AM band

[Terry]

As the years have passed the noise on AM has increased to the point that I can receive listenable signals on local stations only.

A few days ago the noise here increased so dramatically that I decided to hunt it down. By shutting off breakers in my house one by one I eventually found a 5V transformer (wall wart?) that caused the interference. Replaced it; things got quieter.

Then today the power company was working nearby and shut off all of our power and all of our neighbors'. I grabbed my radio to check the noise. There was almost no noise. I could hear 1580 in Springville, 750 in Price, 1340 in Heber and 580 in Boise for the first time. And KVNU 610 and KYAH 540 sounded like local stations. For a few minutes I felt like I was back in 1958.

Then the power came back on. KLO 1430 and KJJC 1230 now barely rise above the static if I turn my radio the proper direction.

But I wouldn't give up my computers and cell phones.

[kenglish]

When someone asks, "What can cause radio and TV interference?", I usually hand them a dictionary. So many things, natural or electrical, can cause RFI.
Wall-warts are the worst. I like to wrap the DC output wires through ferrite cores, and do the same to the AC cord, if there is one. This is a necessity with Switch-mode Power Supplies (SMPS), but also helps on transformer-based units too, by helping isolate the DC from the power line.
Those little monsters that are used to charge cell phones are really bad. A snap-on ferrite helps on them.
Many serious DX'ers and hams run their radios on large batteries, and even replace non-radio wall warts with linear power supplies.
Computers, and anything with a microprocessor inside, can make noise, and can use a ferrite.
Be aware, though...ferrites come in different "flavors", called their "mix". They are made of epoxy and a mix of one to (maybe) three types of powdered metals, which are resonant at certain frequency bands, and convert the noise to miniscule amounts of heat. Most of the ones on Amazon, e-Bay, etc are not marked, and don't help at MW or SW frequencies. They are usually surplus from computer manufacturer inventory. A 75 or 77 mix is better for radio. The non-labelled ones are usually for VHF.
You often need several different types in series to quiet a wide band of frequencies.
Palomar Engineers has lots of info and specific kits on their site.

[kenglish]

Other common noise generators are light bulbs and dimmers. Plain old incandescent light bulbs are usually quiet, but fluorescent bulbs, and many LEDs are noisy. You have to shop around for quiet fluorescent, sometimes adding ferrites or line filters. LED bulbs can be frustrating... poor manufacturing practices can make them noisy, as well as failure-prone. I have a friend in Germany who has had to give up on radio, because a vindictive neighbor keeps using a bad LED bulb to harass him...even after my friend installed a good one for him.
As for dimmers, look for ones that are specifically labelled as "RFI-filtered".
Also, garage-door dealers sell specially-filtered screw-in bulbs, since commonly-available ones often jam the door-opener's receiver.

[kenglish]

The next culprit, and the one that often gets first blame, is power lines. They often conduct noise from one user to another.
They can generate noise themselves, though, due to damaged components and other (correctable) maintenance issues. Broken or dirty insulators, damaged lightning arrestors, or missing (stolen) ground wires often are the problem. Try your inside stuff first (and, your neighbor's), then note days, times and weather conditions that can help determine what is happening. Call the Power Company and ask their RFI Investigator for help. Don't be timid...noise is an indication that something is wasting valuable energy, and is going to eventually fail and cause an outage.
Nowadays, you may have to play a bit of "CSR Roulette" though, since some are not aware of the company's protocol.

Researching on the internet, or in Ham Radio books, you can find some fascinating reading. The ARRL even has a link to a Naval Post-Grad School book on RFI prevention for radio receive sites, that gives a lot of food-for-thought.

[CAwasinNJ]

The interaction between garage door openers and bulbs is something I'd never thought of before but it makes sense. Those openers can be tricky to get to trigger even WITHOUT a bulb interfering.

I've had some experience with dimmers. Sometimes the amount of noise varies with the amount of dimming it's doing, sometimes it isn't. I had the misfortune of dealing with a particularly bad one 30+ years ago. It was a photoelectric one that came on gradually as it got dark. Even when it was fully on that sucker emitted everything from DC to daylight and at a very noticeable distance. Completely ruined any DXing even on a battery powered radio.

[kenglish]

hackaday.com/tag/radio-frequency-interference/

[David]

The photoelectric "on at dusk, off at dawn" dimmers are definitely one of the worst RFI emitters ever. I ditched the one I had years ago, because it generated a hellacious amount of noise from the bottom of the longwave band up to the mid range HF frequencies whenever it was on. Because of the age of my house, I only have a handful of fluorescent light fixtures, and to reduce RFI I've avoided using CFL or LED bulbs in any of my incandescent fixtures. I bought a couple of cupboards worth of the old style incandescent light bulbs before they were banned a few years ago, and I've still got enough to last for five more years. My monthly electric bill is certainly higher using the incandescent bulbs than it would be with CFL or LED lighting, but the reduction in noise on the AM broadcast and HF bands is worth the extra expense to me.

If there's a power pole transformer in your neighborhood that's going bad, the noise generated by that sucker can be heard 2-3 miles away. I think that's one of the reasons why there was so little noise on the AM band a few weeks ago when the high winds knocked out the power in parts of my neighborhood. Even though I never lost electricity at my house, many of the businesses in the area between 12TH and 20TH streets in Ogden had their power knocked out for up to 24 hours. Just about the time that KOGN 1490 came back on the air was when the RFI on AM broadcast returned in my neighborhood.