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Author Topic: Broad Spectrum RF Noise from LED Bulbs in Church Sanctuary  (Read 2302 times)

Keith Broughton

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Re: Broad Spectrum RF Noise from LED Bulbs in Church Sanctuary
« Reply #10 on: March 12, 2018, 06:11:52 am »

Just a final follow-up on this issue in the event it may help someone else in the future.  Replaced all the TCP Lighting LED bulbs with Cree equivalents and the RF noise is totally gone.  Signal meters on the QLXD receivers now all show zero bars with no wireless mic transmitters on.  With transmitters on, we get a full four bars of signal and no drop outs.

So the moral of the story is don't cheap out on LED bulbs if you intend to use them, and test a sample of what you intend to buy before you get the entire lot you may need.  In our case I purchased the minimum quanity I could of the A19 and BR30 Cree bulbs and tested.  Even held directly against the half-wave antenna while powered on in a lamp test fixture they produced no noise.  I swapped out the 120 LED bulbs for the new Cree models this past Saturday and our problem was solved.
Thanks for posting a follow up.
Glad you got it sorted out :)
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Terry Martin

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Re: Broad Spectrum RF Noise from LED Bulbs in Church Sanctuary
« Reply #11 on: March 13, 2018, 03:15:21 pm »

Thatís good info.  Iíve wondered about some of the cheaper LEDs affecting our IEMs.  We get noise occasionally - depending on the club we are at (same town, in some cases). 
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Rick Earl

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Re: Broad Spectrum RF Noise from LED Bulbs in Church Sanctuary
« Reply #12 on: March 13, 2018, 03:37:16 pm »

Just a final follow-up on this issue in the event it may help someone else in the future.  Replaced all the TCP Lighting LED bulbs with Cree equivalents and the RF noise is totally gone.  Signal meters on the QLXD receivers now all show zero bars with no wireless mic transmitters on.  With transmitters on, we get a full four bars of signal and no drop outs.

So the moral of the story is don't cheap out on LED bulbs if you intend to use them, and test a sample of what you intend to buy before you get the entire lot you may need.  In our case I purchased the minimum quanity I could of the A19 and BR30 Cree bulbs and tested.  Even held directly against the half-wave antenna while powered on in a lamp test fixture they produced no noise.  I swapped out the 120 LED bulbs for the new Cree models this past Saturday and our problem was solved.

I was lecturing to a college class about best practices for wireless mics, and I thought this would be a good example.   I went out to my local big box home store and bought the store brand LED bulb hoping to get some nice noise to show up on the analyzer.  I got it home and plugged in the light.... Nothing... I move it closer... still no difference in the noise floor.  Discouraged,  I started playing with other things around the house, I remembered an evaluation video lighting panel that I was testing for it's light quality, and  when I fired it up about 5 feet from the antenna the noise floor jumped almost 20dB!  This is a fixture that is supposed to retail over $1000.00.  It did drive the point home with the class.  It also was a great way to demo directional  antennas.   
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John Roberts {JR}

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Re: Broad Spectrum RF Noise from LED Bulbs in Church Sanctuary
« Reply #13 on: March 13, 2018, 04:51:08 pm »

I don't know that this is a diode "cost" issue but diode speed and a subtle noise interference related to reverse recovery current and carrier depletion. A common remedy in sensitive designs is to place a small snubber capacitor in parallel with the diode junction to damp high voltage rate of change. In several decades of general product design I never had a diode noise issue, but have seen and heard about the common mitigation strategy (capacitor snubbers).

I can imagine a low cost lamp manufacturer being reluctant to add JIC parts (snubber caps). They may be in violation of some FCC emissions regulations (not my area of expertise). So not a component cost issue per se, but clearly a less respectable manufacturer (if it wasn't tested for emissions).

JR
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Keith Broughton

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Re: Broad Spectrum RF Noise from LED Bulbs in Church Sanctuary
« Reply #14 on: March 13, 2018, 05:04:41 pm »

JR...I like your signature. ;)
Had not noticed it before.

I guess there is no easy way to know if an LED light has been tested for RF noise unless specifically stated on the packaging.
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Rick Earl

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Re: Broad Spectrum RF Noise from LED Bulbs in Church Sanctuary
« Reply #15 on: March 13, 2018, 05:12:17 pm »

I don't know that this is a diode "cost" issue but diode speed and a subtle noise interference related to reverse recovery current and carrier depletion. A common remedy in sensitive designs is to place a small snubber capacitor in parallel with the diode junction to damp high voltage rate of change. In several decades of general product design I never had a diode noise issue, but have seen and heard about the common mitigation strategy (capacitor snubbers).

I can imagine a low cost lamp manufacturer being reluctant to add JIC parts (snubber caps). They may be in violation of some FCC emissions regulations (not my area of expertise). So not a component cost issue per se, but clearly a less respectable manufacturer (if it wasn't tested for emissions).

JR

This fixture is supposed to be "flicker free" for film and video applications,  It makes me wonder if it's the diodes or if there is some high frequency switching in the driver that is causing the noise. 
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John Roberts {JR}

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Re: Broad Spectrum RF Noise from LED Bulbs in Church Sanctuary
« Reply #16 on: March 13, 2018, 05:29:50 pm »

This fixture is supposed to be "flicker free" for film and video applications,  It makes me wonder if it's the diodes or if there is some high frequency switching in the driver that is causing the noise.
LEDs are DC devices (only conduct in one direction). To make light from AC the voltage must be rectified.

Driving LEDs from half wave rectified 60Hz will generally not be perceived as flicker, but full wave rectification bangs them 2x per cycle (Hertz) for even less on/off duty cycle.

JR

PS: Is the subject lamp FCC listed?
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Bill Meeks

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Re: Broad Spectrum RF Noise from LED Bulbs in Church Sanctuary
« Reply #17 on: March 14, 2018, 12:02:19 am »

The LED bulbs that caused our problem were in the neighborhood of 4 to 5 years old.  They were bought and installed before I was responsible for the sound system.  The stamp you want to see on LED bulbs is FCC Part 15 compliant.

LED bulbs that are made to screw into the old standard 120 VAC sockets contain very small switching power supplies on a little circuit board in the bulb's body.  The power supply is converting the AC from the socket into a DC voltage for the LED modules that give off the light.  The RF noise comes from poor design of that switching power supply.  The switching supply is used to gain efficiency and dispense with the need for a large conventional iron-core transformer, and it also comes into play with the dimmable bulbs (which our troublesome ones were).

I think all of the bulb manufacturers have been getting better in terms of RF noise output, so it may be that most bulbs in the retail stores today are OK.  I would say that's especially true if they are made by Cree.  Cree also makes some "house brands" I believe for the big-box stores.

Bill
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Keith Broughton

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Re: Broad Spectrum RF Noise from LED Bulbs in Church Sanctuary
« Reply #18 on: March 14, 2018, 07:10:28 am »

  The stamp you want to see on LED bulbs is FCC Part 15 compliant.


Bill
Just checked some bulbs I bought and , in very small print, it says "this device complies with part 15 of FCC rules"
Good to know. :)
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Rick Earl

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Re: Broad Spectrum RF Noise from LED Bulbs in Church Sanctuary
« Reply #19 on: March 14, 2018, 09:03:24 am »

PS: Is the subject lamp FCC listed?

It is a beta test product, I was asked to evaluate it for it's light quality, it just happened to be handy when I was looking for UN-intentional transmitters for a wireless demonstration.  I let the manufacturer know about the RF noise, they said they were aware and working on some changes to address the issue.
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