[Elecraft] OT: Street lights - for US hams only

[Al Lorona]

Yellow sodium vapor street lights can be a significant source of nighttime RFI on the lower bands. They are ignited at dusk by an RF arc that typically lasts between 5 and 10 seconds, the lamp lights, and the arc is extinguished. This arc noise sounds like a constant, dense static and is easily seen as a higher noise floor of up to 10 dB on the screen of a P3 panadapter or equivalent, depending on how far the street light is from your antenna.

The problem occurs when the lamp reaches end-of-life. After turning on for the first time in the evening it will go off again after a period of seconds or minutes and must be ignited again.  Therefore, every so often the noise floor suddenly rises, stays there for some time, and then returns to normal after the lamp re-lights. This cycle can repeat several dozen or hundred times per evening until it turns off for good at sunrise. 160, 80 and 60 meters are the bands most affected by these lights.

I have been able to lower my ambient noise floor by several dB by going out on 'street light patrol' at night, armed with a flashlight, MP3 recorder and roll of bright orange tape. I drive around out to about a mile from my house looking for street lights that are cycling on and off. An efficient way to do this is to look for street lights that are off and watch them for a few minutes to see if they come on again, while listening on the car's AM radio for the characteristic interference. When I find an offending light, I use the flashlight and record the location, pole number, and any other important information on the audio recorder. Then I mark the pole with the bright orange marker tape and continue to search for other lights. On a good night, I can find 5 or more lights within a radius that I know can cause RFI at home. I have found that lights a half mile away will raise the noise floor only a couple of dB, while those within a block or two can add 10 dB to the noise floor.

My local electric utility has a web site to report street light outages. I simply log in and transfer the information from the MP3 recordings to the form on the web site and submit the report. I'm extremely fortunate that my utility, Southern California Edison, faithfully replaces lamps within a business week of my report. They like several reports at once which makes it worth their while to spend a day replacing lights in one area, and they also appreciate the orange markers which helps them sight the poles easily.

A few poles in my city are owned by the city, not the electric utility. In that case, I have made friends with the city worker in charge of taking outage reports and so I have someone to e-mail my reports to. Interestingly, the city can take several weeks to replace a bad lamp. [Government always seems to be less efficient than business.]


I encourage you to be vigilant for sodium vapor street lights that could be a large source of HF nighttime interference for you.


Al  W6LX