As a Utility Interference Investigator, I run into bad street lights all
the time. The most common failures are cycling and constant "invisible"
RFI.
The cycling failure is fascinating. The photocell senses that darkness has
fallen. The light begins the process of coming on. The bulb will begin to
illuminate dimly and its brightness will increase slowly over about a
minute. At the end of the minute the bulb reaches full brightness and stays
lit at full brightness for about 10 seconds. After 10 seconds at full
brightness, the bulb goes dark. The light stays dark for about 30 seconds
or so and the process repeats.
Listening with a radio tuned to a quiet spot (or 1710) on the broadcast
band, you can usually hear the repetitive street light symphony. Sometimes
the RFI produced by these failed cycling lights can be heard as high as 325
MHz.
In my region, the cycling street lights can produce the following sounds in
a receiver. As the bulb first dimly lights, the RFI begins. In the receiver
a broadband buzzing modulation can be heard that seems to have a low pitch.
As the street light bulb increases in brightness, the pitch of the
modulated RFI increases in lock step with the bulb's brightness. At full
brightness the RFI's modulation reaches its highest pitch and greatest
loudness. When the bulb goes out 10 seconds later, the RFI stops. In 30
seconds to a minute, the process repeats. The process continues non-stop
until daylight comes. I have never actually determined what causes this
behavior in street lights. It sounds to me light the photocell's electronic
switch has failed and as the current through it increases, RFI is produced.
The only other likely source would be the ballast.
When a street light produces constant, unchanging RFI, it can be heard
strongest at low frequencies. Only 50% of the time have I been able to
detect a street light producing constant RFI at frequencies above 50 MHz.
The light DOES NOT need to be illuminated to produce this constant RFI.
However, it's usually very easy to pinpoint the offending light. Here
again, either the photocell or ballast are bad.
When I report a bad street light, they get fixed without my being present
for the repair. I never know if a contractor will make the repairs or one
of our troublemen. I've spoken to some troublemen who have done street
light repairs but have never gotten definitive answers as to which failure
causes which problem. Sometimes the entire lighthead is replaced and
shipped to an inhouse shop for rebuilding. Sometimes the head is rebuilt on
the spot. I am never told which repair method will be used or when the work
will be done (so I can observe and learn!!)
Like any other RFI source, finding a bad street light requires a
portable/mobile receiver with RF Gain control, signal level indicator and
directional antenna (or sensible technique based on signal strength). Not
all street light RFI manifests itself as visible light. However, it can
always be heard. Good DFing tools and technique will get the problem
located promptly so repairs can be ordered.
Good luck!
Frank N. Haas KB4T
Utility RFI Investigator
Florida
-----Original Message-----
From: RFI [mailto:rfi-bounces@contesting.com <rfi-bounces@contesting.com>]
On Behalf Of N1BUG
Sent: Sunday, November 24, 2013 6:17 AM
To: RFI@contesting.com
Subject: [RFI] Street lights
I'm wondering about noisy street lights - specifically the pattern where
noise is present for a couple of minutes, then goes away for a similar
period of time. It has been said the noise is due to the light trying to
restart after going out. Is it a reasonably safe bet that any street light
making this on/off RFI will be visibly going out and restarting?
I'm wondering if I really need to drag all the RFI tools out with me on a
street light hunt. If the light is visibly going off/on I should be able to
find it visibly and confirm it's the one by listening to audio from my home
receiver via some wireless link, correlating to cycles of the light. No?
Just wondering here.
73, Paul
--
Paul Kelley, N1BUG
RFI Committee chair,
Piscataquis Amateur Radio Club
http://www.k1pq.org
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On Sun, Nov 24, 2013 at 6:16 AM, N1BUG <paul@n1bug.com> wrote:
> I'm wondering about noisy street lights - specifically the pattern where
> noise is present for a couple of minutes, then goes away for a similar
> period of time. It has been said the noise is due to the light trying to
> restart after going out. Is it a reasonably safe bet that any street light
> making this on/off RFI will be visibly going out and restarting?
>
> I'm wondering if I really need to drag all the RFI tools out with me on a
> street light hunt. If the light is visibly going off/on I should be able to
> find it visibly and confirm it's the one by listening to audio from my home
> receiver via some wireless link, correlating to cycles of the light. No?
> Just wondering here.
>
> 73, Paul
>
> --
> Paul Kelley, N1BUG
> RFI Committee chair,
> Piscataquis Amateur Radio Club
> http://www.k1pq.org
> _______________________________________________
> RFI mailing list
> RFI@contesting.com
> http://lists.contesting.com/mailman/listinfo/rfi
>
--
Frank N. Haas KB4T
Utility Interference Investigator
Florida
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