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Re: [RFI] LED traffic signals

To: rfi@contesting.com
Subject: Re: [RFI] LED traffic signals
From: digital-conjurers@roadrunner.com
Date: Sat, 15 Dec 2007 17:44:16 -0800
List-post: <mailto:rfi@contesting.com>
I live in San Diego, and we have these LED sigs all over the place; I 
listen to AM a lot, and have detected no problems...and I put on 25,000 
miles in a year in this environment, too, at all hours of the day and 
night.  Listen to KGO 810 at night too, 500 miles off.

Perhaps this is an indicator that it's _manufacturer-specific_?   Someone 
saving .13 per unit so the shareholders can get an extra .05 per share 
dividend, probably.

"No-one spends more than the stingy engineer."

As a side note, many years (1990) ago those HV Neon "WALK/DON'T WALK" signs 
went up, and created a 1000 foot radius howl on HF like you would not 
believe.  SDG&E in conjunction with the Street Maint. Dept. came right out 
and fixed the problem with a simple filter/ground screen combo.

Some utilities are better than others.

Just my .02 .



At 12:43 PM 12/14/2007, you wrote:

>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
>The best games are on Xbox 360.  Click here for a special offer on an Xbox 
>360 Console.
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