[RFI] LED Street lights

Thu Aug 24 06:35:10 EDT 2023

There is nothing incorrect in what Jim Brown said at all, and he is certainly NOT telling people not to start near the device.  He is explaining a nuance that is important to understand to avoid a common troubleshooting error.

For the most part, on HF, devices themselves do not radiate much, but the wires that they are connected to do.  That is what Jim is explaining.

How that radiation decays with distance depends on how the noise is being conducted onto the wiring.  If the wiring were reasonably well balanced, acting like a leaky transmission line, the strength of the noise would decay at about 60 dB/distance decade within about 0.16 wavelength from the source and/or the source wiring.  If the noise is conducted to the wiring as a common-mode signal, the decay rate would be lower and, if the wires are long in terms of wavelength, a standing wave along them is often developed, with peaks and valleys that can very much confound locating the actual device source.

To understand what Jim Brown is telling you, think of an LED bulb. It is too small to be an effective HF antenna, but those long wires it is connected to can be great antennas. If the noise from an LED street light conducts around (or through) the step-down transformer it is connected to and gets onto those overhead distribution lines, it can radiate for quite a distance an in some instances, may be stronger at some point other than right at the pole it is attached to, depending on what antenna you are using for receive. (A loop receive antenna may show a NULL when the null is pointed at the source, and as you drive away, that null will disaappear.)

I have retired from HQ, but still volunteer there (quite a bit of time on this SMC HF petition.)  One of my late summer projects is going to be to set up a moble noise-measurement system, using accurate equipment, and by late fall, I expect to be making measurements of noise over large geographical areas.  Measuring the noise from an LED street-lighthing system in an entire community should be quite the challenge.

>From what I have seen in some of the temporary setups I have used over the years, and from just listening on a receiver, most of the LED street lights seem to be RF quiet.   From the reports I have seen, some are not.

What I don't have is make and model number of the LED bulbs that are causing a problem.  I am sure I can persuade the ARRL Lab to buy one and we can make measurements of its conducted emissions.  That will be a good starting point.  If FCC follows its own lead on past decisions, it will proclaim those overhead lines to be "non-residential" environments, as it did for BPL over a decade ago, even for street lights in residential neighborhood.

Ed Hare, W1RFI, ARRL Lab Volunteer

________________________________
From: RFI <rfi-bounces+w1rfi=arrl.org at contesting.com> on behalf of AA5CT via RFI <rfi at contesting.com>
Sent: Wednesday, August 23, 2023 9:27 PM
To: rfi at contesting.com <rfi at contesting.com>; Jim Brown <jim at audiosystemsgroup.com>
Subject: Re: [RFI] LED Street lights

I don't know where you're coming from Jim. How long has it been since you've been in the 'field' with a portable SW receiver?

Noisy devices, power poles, even lighting poles all have distinctive signatures heard when standing near them. The CLOSER you get the STRONGER will be whatever noise/signal the device *may* be generating. Surely this aspect need not be spelled out?

I still stand with the advice as a first tier investigation to GET NEAR THE DEVICE and inspect the ham bands for any anomalous noise. This isn't rocket science. This e-mail was a response to Eric for advice looking at a NEWLY installed LED lighting pole. Eric, if you have a SW/HF radio in the car that might be a way to do a first tier/first pass inspection of the new lighting pole too.

 de AA5CT Jim

---------------------------------

    On Wednesday, August 23, 2023, 7:54:53 PM GMT-5, Jim Brown <jim at audiosystemsgroup.com> wrote:

 On 8/23/2023 5:17 PM, AA5CT via RFI wrote:
> Hmmm ... if an exotic receive apparatus is required to 'spot the noise', how serious could the noise really be?

Not all noise is broadband. Indeed, most electronic noise is not. And
the receiver cited makes an excellent spectrum analyzer. Most noise is
radiated by wiring, not by the fixtures themselves.

NK7Z's webpage provides lots of excellent troubleshooting advice for
chasing electronic noise.

73, Jim K9YC

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