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  #1  
Old 12-16-2010, 04:44 PM
steveparrott steveparrott is offline
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Default RFI with LED lighting

I'm a lighting manufacturer and have started to hear complaints about outdoor LED lights interfering with garage door openers (GDO's). It's a known problem that many electronic circuits can interfere with these RF transmitters/receivers.

After talking with Chamberland, a major mfg. of GDO's, they tell me that RFI can come from other RF devices that transmit at certain frequencies; and it can come from devices that somehow transfer interference over electrical wiring. GDO's typically transmit at 315 MHz.

LED engineers tell me that a properly designed LED circuit will limit or filter unintended RFI. They also say that they wouldn't be surprised if many of the cheap China exports fail to control RFI.

A few questions:

1. Would it be possible that a 12V AC LED circuit could somehow transfer interfering frequencies through it's lead wire, through a torroidal transformer, through the house wiring to the garage door receiver?

2. If that's possible, what could an electrician put in place to block this transmission?

3. Regarding the interfering frequencies, Chamberland tells me that other devices that transmit at the same frequency (315 MHz) can definitely interfere, but other frequencies may also interfere. Can someone explain how this is possible?

4. I understand that RF emissions can be measured with certain equipment. Does the same equipment also measure the sort of frequencies that travel over wires? Are the two types of transmission (air and wires) basically the same?

Thanks for your help.
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Old 12-16-2010, 05:51 PM
Audioguru Audioguru is offline
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Maybe garage door receivers are an extremely simple super-regen circuit that is easily overloaded and picks up all kinds of interference?
Maybe they use simple AM which picks up amplitude interference instead of FM?
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Old 12-16-2010, 08:32 PM
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Backward coupling through the power transformer into the house wiring and AGAIN through another power transformer into the GDO circuit is extremely unlikely. 60Hz power transformer will cause ungodly db loss in a 315MHz signal. The interference will not be getting in that way.

The metal structure of the GDO and the tracks for the door are all metal and some doors are metal as well. Seems the logical entry method for a radio freq signal. Some piece that is a near perfect wavelength or multiple thereof acting like an antenna for the LED circuits operating freq.
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Old 12-16-2010, 08:35 PM
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If you set up any testing situations to achieve the interference condition, you could try simple solutions (cheap) to see if they help, or even cure it.

Isolating the LED circuit with a transformer to remove its reference to the household ground circuit, or conversely, isolating the GDO circuit power from ground the same way to break its tie with any grounded structures. Would be cheap to implement and to test for effect.
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Old 12-16-2010, 09:04 PM
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What are your outdoor LED lights?

How much power, what type of power supply, etc? Are there long wires inside that are regulated with a switch mode power supply? You can try adding a few bypass capacitors across long wires carrying power to reduce their chance of acting like an antenna.

Would need more information about the LED circuit, power supply and drive for ideas of what could be causing the issues.

How far away from the garage door opener are the LED lights that are causing the interference?
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Old 12-16-2010, 09:15 PM
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Other freq. can interfere if they are multiples of the base freq of interest.

So 630MHz 1.26GHz 2.52GHz
Or 157.5MHz 78.75MHz 39.375MHz could all be freq that interfere. Even signals that are merely close to the equipment and not even freq related can interfere due only to close proximity. Remember that annoying noise radios TV's and computers make when your cell phone is right next to them and rings?
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Old 12-16-2010, 09:30 PM
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Hello,

Do you have more details on the leds reciever?

RFI has mainly to do with bad shielding or bad filtering.

See these pages from the EDYCYPEDIA for more info:
http://www.educypedia.be/electronics/emc-emi.htm
http://www.educypedia.be/electronics/componentspas.htm

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Old 12-16-2010, 11:41 PM
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LED's as a potential source of RFI seems unlikely. They operate on/off if twinkly, and do not use PWM schemes for dimming.
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Old 12-17-2010, 12:00 AM
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The most likely source of a multi hundred mega Hertz RF noise is a poorly filtered switching power supply in the LED device. The LED's themselves wouldn't radiate any RF, but a power supply can do so easily.
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Old 12-20-2010, 05:32 PM
steveparrott steveparrott is offline
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Thanks for the replies.
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