[RFI] LED Traffic Light RFI

Cortland Richmond ka5s@earthlink.net
Fri, 27 Sep 2002 12:33:34 -0700


I think I remember this subject being discussed in another venue, 
possibly on YahooGroups. In that case, if I recall correctly, the 
noise was evidently coming from a switching power supply providing 
low-voltage for LED lamps. 

It does not need mentioning that harmful interference requires 
correction. I would not be surprised, however, to learn the power 
supplies used in the lights were NOT in  compliance, the manufacturer 
having evaded that by reliance on the utility exemption Part 15 
provides. However, that exemption does not apply to equipment located 
outside of a utility's facility and harmful interference in any event 
voids it.

I may take a look at a few lights around here (Sonoma County,CA) with a 
receiver or a spectrum analyzer to see what's coming from them.  I've GOT
no one is hiring EMI engineers just now (rueful grin).


William G. McDowell <k4cia@mindspring.com> wrote" 
> Has anyone experienced RFI from these new LED traffic lights?   I live
> 800' from an intersection that has several of them.  A broad band RF
> emission is radiated when the red and green lights are illuminated.  The
> noise stops when yellow (caution) is lit as the lights change.  Sounds
> like line noise on the receiver but its coming from the lights.  I've
> confirmed this by using a portable SW near the intersection.
> Any advice appreciated.  Have called a state traffic light engineer but
> not get a return call yet.
> Yet another obstacle to overcome in this quest for semi-quiet bands.