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@contesting.com> on behalf of AA5CT via
RFI <rfi@contesting.com>
Sent: Wednesday, August 23, 2023 9:27 PM
To: rfi@contesting.com <rfi@contesting.com>; Jim Brown
<jim@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@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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