Chasing down interferance

[DavGoodlin]

This is why I only use incandescent or T12 fluorescents in my shop. The portable drill battery pack charger made interference. I routinely install line filters (M-derived from junk SM power supplies) on the old radios I restore for others. It does make a difference and it is worthwhile adding grounded cords to all restorations.

Most times the noise is NOT on the power line (like AM buzz is from dimmer switches and faulty photocells) but more often noise is radiated at the lamp. The older the better and even the early compact fluorescent lamps with magnetic ballasts were not a problem if they were properly grounded.

But when the ballasts went electronic, it started. I found the T8 lamps on a 2-lamp ballast were only a minor problem but when the 3 and 4 lamp ballasts were used it became unbearable, commensurate with current. Many compact fluorescent lamps with twin, triple or quad tubes (not spiral lamps) had electronic ballasts. I designed lighting for retirement homes. I looked high and low for the least interfering fixtures, even if it meant not using the cheapest OR most efficient ballast.

I tested a bunch of LED lamps once and found the current waveform was very non-sinusoidal on almost all of them. Some generated much more AM and FM noise. The biggest surprise was the waveforms were all radically different. If doing a spectral analysis, a square wave by definition is comprised of harmonics.

FCC EMI limits are outdated, CFR 15 consumer is just a toothless standard. The switch mode power supply SMPS is here to stay, thanks to energy star and other forces to reduce overall consumption.