Author Topic: 120 Hz radiated dimmer noise  (Read 192 times)

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Offline dfroula

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120 Hz radiated dimmer noise
« on: August 05, 2018, 10:28:00 AM »
I have a Leviton "Z-Wave" home automation light dimmer connected to 9 LED flood lamps in the ceiling. This thing kicks up a 120 Hz noise racket that affects both the E and H field Red receivers. I've verified the noise is being radiated and picked up as RF by running my Red system on battery power temporarily.

The Auto Amplitude Adjust feature stops me from going into interference. It allows normal operation to an extent, but the detection rate goes way down.

I'm thinking of trying a large brute-force ferrite toroid choke in line with the output of the dimmer. Has anyone had any success solving this kind of issue?

Best regards,

Don F.

Offline miraculon

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Re: 120 Hz radiated dimmer noise
« Reply #1 on: August 05, 2018, 02:14:44 PM »
Don,

Have you tried substituting an incandescent lamp for the LEDs? (Just as an experiment.)

Some of these LED circuits are quite noisy. For example, if I turn on a LED bulb close to one of my NOAA weather radios, the hash noise increases substantially. I realize of course that the Wx radio is VHF and the detectors are VLF but it can be fairly broadband noise.

Is the noise present at 100% duty cycle on this dimmer (full on), or only at "dimmed" settings?

Can I assume that the 120Hz is the rep-rate and the noise is actually a high frequency pulse?

Greg H.


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Offline dfroula

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Re: 120 Hz radiated dimmer noise
« Reply #2 on: August 06, 2018, 06:49:25 AM »
Hi, Greg,

I have not tried replacing the LED lamps with either incandescent or compact fluorescent, assuming the noise was generated by the dimmer as it abruptly chopped off the positive and negative swings of the AC waveform. The interference appears as single short positive and negative spikes of identical amplitude. The amplitude is constant regardless of the setting of the dimmer, which is not how a traditional manual dimmer and incandescent bulb combo behaves. Curiously, there is no RF hash generated on the ham bands or AM broadcast band.

I’m beginning to think the noise may be generated by the bulbs, so your suggestion seems reasonable. I’ll swap in some incandescents and check the effect.

Rep rate is always exactly 120 Hz. I can kill the noise pulses by increasing the thresholds/lowering the fixed gain and thus reducing the effective gain, but that degrades the station performance below what I’d like.

It seems odd the pulse amplitude is identical on both axes of the H field amps and all channels of the E field. That points to powerline ingress, but running the system off of battery power would seem to eliminate that. Odd.

Best,

Don F.

Offline dupreezd

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Re: 120 Hz radiated dimmer noise
« Reply #3 on: August 06, 2018, 09:35:42 AM »
Don, I would pull the switch out and disconnect the load wire to start with. The will eliminate the wiring and LED's.

Make sure you turn the power off first.  :-)

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Offline dfroula

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Re: 120 Hz radiated dimmer noise
« Reply #4 on: August 06, 2018, 07:56:58 PM »
Lol. 🤓. Bet that would fix it.

Offline dupreezd

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Re: 120 Hz radiated dimmer noise
« Reply #5 on: August 06, 2018, 08:09:26 PM »
lol.
I did not mean to completely remove the switch, just pull it out the wall. Then disconnect the wire going to the lights (load side). The switch will still be receiving power and transmit to the hub. This will indicate if the switch creates the interference back into the main supply lines.

Hope this make more sense.
 :-)
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Offline dfroula

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Re: 120 Hz radiated dimmer noise
« Reply #6 on: August 07, 2018, 07:32:38 AM »
I get your point now, and it makes sense. As it needs constant power for the electronics, the dimmer uses both a hot and neutral lead and has a 3-way smart “companion switch” remote that also requires hot and neutral plus a single traveler wire between them. I guess the control electronics could be injecting noise into the line at the input side. Easily done, as I was playing around with various values of series load inductors to see if they helped. None did? But they were fairly low inductance.

Don

Offline miraculon

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Re: 120 Hz radiated dimmer noise
« Reply #7 on: August 07, 2018, 08:46:22 AM »
lol.
I did not mean to completely remove the switch, just pull it out the wall. Then disconnect the wire going to the lights (load side). The switch will still be receiving power and transmit to the hub. This will indicate if the switch creates the interference back into the main supply lines.

Hope this make more sense.
 :-)

But in this case there will be no current being switched to the load.

I believe that the incandescent sub will tell if the problem is with the LEDs or the Z-wave switch.

LED bulbs are more complex than one might think. They basically convert the AC to DC then buck regulate it down to a voltage (and current) that the LED string can handle. The noise comes from this switching regulator inside the LED bulb. With no load the regulator will probably go into "cycle skipping" that will result in a different noise condition than actual operation with either the incandescent or LED loads.

Which potential source that causes "the noise" remains to be seen...

Greg H.


Blitzortung Stations #706 and #1682
CoCoRaHS: MI-PI-1
CWOP: CW4114 and KE8DAF-13
WU: KMIROGER7
Amateur Radio Callsign: KE8DAF

 

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