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[RFI] LED traffic signals

To: <rfi@contesting.com>, <w1rfi@arrl.org>
Subject: [RFI] LED traffic signals
From: Donald Chester <k4kyv@hotmail.com>
Date: Fri, 14 Dec 2007 20:43:08 +0000
List-post: <mailto:rfi@contesting.com>
I  live in the country with no traffic lights nearby, so this isn't a problem 
with me, but I keep hearing about RFI generated by the new l.e.d. traffic 
signals.  Apparently, the noise is due to a switching power supply used to feed 
the lights, and the power line leading to the unit acting as an antenna.

Someone I know has one of those LED stoplights about 100 yards from his house.  
It wipes out the AM BC Band when you are in the car sitting at the light, and 
he says he can hear it up and down the band and  weaker signals on 75 and 160 
at night are GONE.  He figures there isn't anything he can do about it at all, 
except move.

I wonder if anyone has checked to see if those led traffic lights have been 
certified to meet Part 15 standards.  Since they are becoming ubiquitous in 
almost every city and town and there are traffic lights literally everywhere, 
this could grow into a major rfi problem that rivals or surpasses BPL.  

Perhaps the AM broadcast industry would get involved, since this stands to hurt 
them severely.  Over 90% of the prime time radio audience during morning and 
evening hours is made up of commuters, and most listeners will simply switch 
over to FM if they start getting interference at every traffic light.  This 
could become the death knell for AM broadcast radio, with its odds for survival 
already marginal at best. Those switching power supplies could easily be fixed 
with a little filtering.  I'm not even sure that shielding would be required.  

This is a problem that needs to be addressed NOW before the overwhelming 
majority of traffic signals nationwide are replaced with noisy l.e.d. ones and 
the problem becomes impossible to remedy.

Don k4kyv

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