New ham with new problems

Shortly after getting my license in the fall of 2024, I started to encounter some strong periodic RFI noise across all of the bands. I first noticed it on VHF, looking like little waves or ants crawling across my spectrum graph. Switching from FM to AM so I could hear them in their true form, I think “bees”, or sometimes “huge angry bees” was more appropriate.

Take a listen:

Sometimes it’s just barely noticable, creeping up from my usual sub-S1 noise floor to somewhere around S3 over a couple hours; or invisible on the scope, but present in the audio on the VHF and AIR bands (that was the case for the audio sample above - not even visible on the scope, but highly disruptive to AM signals). Other times it would just come out of nowhere at S7 and make sideband phone operation basically impossible. It could be crashing on and off, or just solid all day. The noise blanker on my rig helps a bit, and the DNR also, but it’s still distracting and hard to listen to, not to mention making the waterfall nearly impossible to read.

Is this PLN?

After doing all of the usual noise-hunting activities starting with my main breaker, I had succeeded in really cleaning up signals all around my shack, but hadn’t made the slightest dent in the angry bees. With a bit of note-taking I noticed that it would disappear with heavy snow or rain, and when spring came around I noticed that hot days would also make it disappear. I began to suspect this could be powerline noise, like a cracked insulator that was arcing, except when the crack is flooded full of water, or it’s hot enough outside for it to expand and close the gap.

So I threw it into Audacity and saw this:

Strong peak at 120Hz and all of it’s harmonics - feeling good about my PLN theory.

Build a yagi

Inspired by W4DD(Jeff)’s presentation called “Locating Power Line and other RF Noise”, I got in contact for advice. We exchanged some emails and he gave me some tips on how to hunt it down, including plans for a simple yagi.

You can download detailed plans for this 137MHz yagi by W4DD here.

On Field Day 2025 I got together with some friends and we built this based on Jeff’s plans.

We were targetting 137Mhz, but it comes out closer to 132Mhz. No matter, that will do just fine, I didn’t even bother to trim it. Note that this frequency is in the air band, so if I’m hearing it there, then it’s possible that pilots are hearing it too when they pass overhead.

Go hunting

Paired with the yagi is my Quansheng UV-K5, which has adjustable LNAs I figured I could use instead of an attenuator. I headed out into the wilderness.

Day 1

There was a clear direction right from my front yard, with the buzzing limited to a roughly 45 degree arc, slightly stronger near the middle. I know there is a small electrical substation in that direction, and figured this might very well be the source. Very optimistic! I followed my ears, the on-screen meter, and the shape of the streets.

This is when I encountered my first curious onlooker - “Are you tracking an animal?” I explained that I was a ham radio operator and what I was doing, and we had a great conversation about his dad and grandpa, and how old technology is so fascinating. He suggested I look into ground wave radio.

No animals, but I did manage to find some noise. First a construction crew operating a large drill and pump, then a pair of power poles with broken grounds. Both were pretty visible on the meter, but didn’t seem to be the source of the buzzing noise I was actually chasing.

Back on the trail, the meter led me toward a suburban strip mall where a pharmacy was running lighting that seemed to really clock on my meter. When I got to the edge of the building though, I found that the lights were joined by another hot spot - the small electrical substation that I suspected was the culprit. The buzzing and the meter lined up! Walking towards the substation, there was a minor but steady increase, so I was definitely on the right vector, but then I walked right past it. In fact, I went two blocks away (off-vector because of the shape of the streets), and clearly the buzzing was from some further source. From the other side, the substation barely showed on my meter; certainly less than the pharmacy.

Calling it a good first day, I returned home happy that my gear was working, but feeling like this might be somewhat harder than I envisioned.

Day 2

The second day was a short one. I came at the target from a different angle and made a bit of progress before it got too warm and the noise disappeared.

Day 3

Drawing the approximate vectors from the previous two outings on a map, I decided to start in a nearby park that was well beyond the substation. Sure enough, the noise was leading me further away. On a nearby block I spotted some old power poles with some rusty looking hardware in the direction of the buzzing, and also encountered my next set of curious onlookers - “Mind if I ask what you’re doing?”. “Sure!” and I explain again. They wished me luck and we parted ways. After another block or two of following the power lines, it was time to call it for the day.

Day 4

Didn’t make much progress on the next outing. The rusty power poles were a red herring, and I kinda went in circles with the shape of the streets making it hard to stay on vector. Again got asked about tracking an animal; I let them know that they weren’t the first to guess that. I gave my now-refined explanation, and got a story about some broken power insulators near their cottage in exchange. I resolved to start my next search at another nearby park which seemed to fit the triangulation, and from which I can see the residence of a fellow ham. It’s easy to tell that a ham lives there by the presence of a magloop, vertical, hex-beam, and dipole all strung around the roof.

Day 5

I started from the park as planned, and it pointed me along some power poles towards a parking lot with bright lights. At the end of that lot I heard the buzzing from an office building across the road (actually it’s two roads that meet in a V). So I crossed over to the office building, then lo and behold, the noise was coming from back the other way. The source was somewhere in the 50m or so between these two lots!

I crossed back over to the land between the roads, and saw a couple very suspicious looking power poles. Lots of big hardware, looking really old and rusty. Standing between them, and on either side, it was clear that neither was really the source, so I swung around 360 degrees and found it. I approached the source, moved to the other side and pointed back. Feeling more certain, I circled it from all sides. There remained very little doubt. I think I’d found it.

Paydirt

I returned two more times, once on a “quiet” day when the noise, if present at all, was not readily perceptible on any band. I didn’t register any substantial buzzing at the source, and was reading noise of -118dB on my HT. Later, I returned on a “loud” day when it was audible and visible on all bands; the buzzing was extreme at the source, measuring -94dB from the same location with the same LNA settings.

All remaining doubt has been erased, I’m quite sure that I’ve found it, just over 1.2km from my QTH.

BEHOLD, the likely source of my interference:

To be continued…

Now that I’ve found it, the next trick is to get someone to care enough to fix it. I’m a bit disappointed that it isn’t a power pole, because I hear the power companies are usually eager to help. I’ll give them a call, but in my case I think I may to follow up with the property owner, or ISED directly, and I’m not sure how that will go.

Stay tuned for Part 2.

---