I have been investigating some powerline noise that cropped up here. As far as I can tell it isn't coming from anywhere inside our home. We recently got new neighbors, and I suspect the noise is coming from over there. We do have a PZZ01 whole-house blocking coupler, but it does nothing to eliminate the noise. The noise is actually slightly stronger when the blocking coupler is “on line”. It is possible that the noise is originating on the opposite phase from my lab, and the blocking coupler helps to propagate it across the phases.
I have been monitoring the noise through the XTB return signal amplifier because that removes most of the AC component. I took some photos showing the noise by itself and with a weak X10 signal embedded in it. Since the X10 burst occurs immediately after the zero crossing, the noise source apparently does not have enough voltage to operate at that point in the waveform. So that leaves a small open window for the X10 burst. The XTB-IIR will recover that X10 signal and repeat it just fine.
I also looked at a minor mod to the XTB that adds a bandpass filter to the return signal amplifier. The photos show the bandpass filter does reduce the noise somewhat. However, the noise source appears to be coming from a switching supply that runs very close to the 120KHz X10 carrier frequency at the peak of the waveform. As a result, most of it gets through the bandpass filter at that point. As the frequency drifts away from the X10 carrier frequency, the bandpass filter rejects most of it.
The X10 signal bursts are more clearly seen with the added bandpass filter. The wandering 3rd phase burst can also be seen, which is a characteristic I had previously noted from the RR501 X10 transceiver.
Noise by itself:
http://jvde.us/x10/line_noise_XTB_X10-in.jpgNoise with X10 signal:
http://jvde.us/x10/line_noise+X10_XTB_X10-in.jpgNoise through BPF:
http://jvde.us/x10/line_noise_XTB_X10-in+BPF.jpgNoise with X10 signal through BPF:
http://jvde.us/x10/line_noise+X10_XTB_X10-in+BPF.jpgUPDATE: The noise has been identified as coming from a 120V 4-watt Lumoform 240 lumen E27-base LED light. I installed this to provide some background light in an otherwise dark interior hallway last spring. While controlled by a Leviton X10 switch, the light is left on 24/7 because it lights the way to the bathroom at night. The X10 switch had been used to dim the previous incandescent bulb to a lower level at night.
When first installed, it worked fine with the Leviton X10 switch, and I did not see any noise. Since the noise started months later after the new neighbors moved in, I never thought to re-examine this particular LED bulb. However, I had read a report of someone else having trouble with a 120V LED light, so I thought I'd check this again. Sure enough, it is now a significant noise source - so bad that the Leviton X10 switch controlling it no longer works. I confirmed the Leviton switch was OK by substituting an incandescent back into that fixture. Since the noise is very close to the X10 frequency band (I measured 117KHz), I suspect a Leviton 6287 filter will block it.Jeff
Author
Topic: Powerline Noise (Read 40179 times)