Radio Reception - Massive Electrical Interference

Maybe a variable-frequency drive for an induction motor in some HVAC blower. Those things are super bad news. Or it might just be a whole building full of SMPSes.

Cheers

Phil Hobbs

It happens only to radios brought into this bathroom. Lots of static on FM, intermittent multiplex(stereo for the young uns!) and loud static and that buzzy-shriek right below

80 on the standard dial(AM).

Once the boombox is moved somewhere else in the apt, it performs like a normal set.

This is (an example of) what I can see in the upper LH corner of my bathroom window:

A big honkin one, twice the size of a residential service! And the closer a radio set gets to that thing, the worse it buzzes

With Radio reception, you can have architectural interference in a building or a residence for a myriad of different reasons. Here, you have electrical power interference as well as other metal (including aluminum) which inhibit radio waves from travel through it. If you have a table radio or a portable, try moving the device closer to a window or area with open air. Since you moved in and the place is new, I take a portable radio (an FM radio) from a cell phone or bike radio and walk around to find out where the best reception is. This is a trial and error approach. I then due this for AM and see if and where the best reception is for AM and FM, what direction the antenna is pointed, how far away, etc...

I do this to find the best range within the dwelling. I usually add an antenna to the device (if it has a telescopic antenna, you can clip additional wire to the top of the antenna with the clamp portion of the clip being conduction and the handle being non-conductive), so you can get more range and better reception.

AM is amplitude modulation and the signal is modulated by the height (amplitude) of the radio wave. FM is frequency modulated (is wider band than AM) and uses line of sight reception. FM is in a higher band than AM. FM is shorter range and more power. AM is longer range and less power.

These concepts apply to the wireless internet as well. Key is a good open area to provide an adequate reception envelope. Good Luck and God Bless.

Sincerely,

Charles Lucas

Well, there's more loop area there to spray magnetic fields around than there is in the cables in the wall. The nasty high-frequency currents are probably coming from VFDs, switching supplies, and so on.

I build a lot of sensitive front end amps in instruments, so I feel your pain. You still hear people advocating for star grounds, split ground planes, and so on. Those were great in 1950, but in 2022 there's so much RF and miscellaneous hash running round that a split ground plane is as good as an antenna.(*)

Cheers

Phil Hobbs

(*) There are fairly popular antenna designs based on slots and patches in planar conductors.

______________

The point is, it's an issue, especially at certain parts of the AM dial, when a radio is within 10 feet of the service mast outside my bathroom corner window. Outside of the bathroom corner of the apt, the interference drops off exponentially.

On the ground floor is a light-industrial classification, prefabing shower doors and such. No loud hums or buzzes every time material is cut or edges chamfered. Nothing like that at all. Just a steadily increasing noise the closer one gets to that bathroom window. The radio sits on top of a toilet about 8 feet from that corner of the bathroom

_______

Should an electrical service mast like the one I linked to cause that level of EMI?

The mast itself is not the cause. It is a non conductor. It is possible there is arcing between the wires inside the mast, but that is not the mast causing the problem. If arcing is occurring, it's due to frayed insulation on the wires. And I only mention it as a possibility, not a diagnosis. Another possibility is corroded/loose "bugs" ("utility splices" on your diagram). Again, not a diagnosis, but a possibility. But either of those conditions - arcing within the mast or bad connections at the top of the mast could make one think that the mast is the cause of the problem. Take a portable radio to the utility electric meter at the service entrance and see what you hear with the radio held near the meter.

Ed

By itself, no. It ought to be a fairly passive pass-through for AC current, with no mechanism for generating RFI. If there's a loose wire or other bad connection, it could be making noise (and possibly overheating and creating a safety hazard).

Seems to me there are two possible sources of the RFI you are suffering:

(1) Industrial equipment on that line (welders, big brush motors, switching power supplies) which are generating RFI internally and feeding it back into the mains. Here in the US, "Class A" equipment (for use in business environments) is allowed a lot more RFI leakage than "Class B" (residential), and industrial equipment is even worse.

(2) A physical fault in the mains wiring, which is causing arcing and sparking, corona discharge, and so forth. Two fairly common problems on power distribution poles are bad insulators (with electricity arcing over them) and loose or defective ground connections. Arcing in a circuit-breaker panel (e.g. a breaker going bad) could have a similar effect.

In both cases the noise can travel quite a long distance along power wiring to the point where it troubles you.

There are a few ways that can be used to track the location of a noise source or fault of this type. Corona discharges and arcs often generate a lot of ultrasonic noise, and there are ultrasound receivers with directional microphones which shift this noise down into the audible band. Arcing and corona can also generate noise up into the VHF band which can be tracked using a receiver and a directional antenna (e.g. a small hand-held Yagi). A spectrum analyzer hooked to a directional antenna can be a useful tool as you may be able to see specific noise lines bouncing up and down.

____________________ But close to that mast, in this apartment's bathroom, is where the interference is strongest, out to perhaps a ten foot radius, which covers most of this bathroom. Beyond that, the interference is, at worst, negligible.

And I understand that the head of the service mast - the part visible above and to the left of the bathroom window, is only part of the package. I will take outside a small portable radio, and walk around within 8 feet of the meters at the base of the service mast, and see what happens at the frequency of the AM station I listen to.

Nice job deducing the likely point of entry. If your apartment building has the usual array of smartmeters, see if the noise is also coming from one particular smartmeter. You may need to REDUCE the sensitivity of the AM radio by partially covering it with aluminum foil.

Some questions and comments:

1. Is the noise present all the time or does it go on and off? If it does one and off, try to correlate the timing with something in the area the goes on and off at the same rate.

1. Does the noise appear (in the bathroom) at every frequency on your radio? If you have an HF/SW radio, try different bands. If you have a directional BCB antenna, such as a loop or ferrite rod antenna, you might be able to find the source by direction finding.

2. If you have an oscilloscope, or a laptop with a sound card running a software oscilloscope, try to get a screen print of the AM noise. This will tell me something about what might be producing the noise. Extra credit if you an SDR dongle and can produce a spectrum analyzer output. If this is too much work (which it probably is), make an audio recording of what you're hearing on the AM receiver and post the MP3 file somewhere so we can analyze it. Try to make the recording listening to a normally blank spot on the AM dial so that you're hearing only the noise and not an AM station mixed with the noise.

1. Jumping ahead, if the noise is there 24x7 and never goes away, then you're dealing with some kind of noisy device built into the local infrastructure. Such a source is going to be difficult to find and even more difficult to get the city to fix.

2. If the noise goes away at night, my guess(tm) is you're hearing noise produced by a PV (photovoltaic) solar inverter. Most vendors have EMI/RFI reduction kits available. If you have solar panels on your roof or nearby, it might be a possible source. Something like these. Make sure there's plenty of attenuation at BCB (broadcast band) frequencies:
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3. Check if your favored AM station is streaming on the internet or does simulcast on an FM frequency. The interference might be less and the filters more effective at 100MHz.

Good luck.

"Doctor, doctor! It hurts when I go like this!"

"So don't go like that." ;)

Cheers

Phil Hobbs

You should check the ground connection of the power conduit, where it meets the service entrance.

Your boom box possibly has a screw connection marked 'antenna' for a straight wire, or a telescoping antenna - both are usefull for FM directional preferential reception. You may have to engage a switch somewhere to select either.

You can forget about AM. In the region of any concentration of commercial, residential or tranport activity, reception will be noisy at best.

RL

It's possible that the bathroom has a big mirror (which is a conductor, so shields/reflects RF) and that's part of why reception is poor. Move the radio to different spots, and if you find a place that DOES have reception, consider mounting a shelf there...

A fluorescent ballast can be a major noisemaker; have you tried switching things off in the vicinity?

Most AM noise I've found is worse between 700KHZ - 1MHZ. At my house, the AM is almost unlistenable, and I'm in the middle of a 5 acre lot. What I found by shutting off all breakers and turning them on one by one was several items contributing to the din. I found my outdoor motion sensing light fixtures were causing noise (took them apart and hard wired them then added Honeywell wall dusk to dawn switches), my alarm system (added low value capacitors across all keyboard lines at the panel), but the biggest offender was my wifi router. I took it apart and found the PFC cap bulged and changed it. It cut the noise down but it still generates a racket.