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LEDs may be lights out for your wireless mics

As if there weren’t enough challenges facing us from shrinking bandwidth, new cell phone service in the 600 MHz band and whitespace devices such as the new Microsoft project.

Here’s one you may not have yet considered, namely broadband RF interference from LED lighting.  Lately I have been receiving more customer service problems that have turned out to be directly related to the installation of LED stage lighting and even general utility lighting as businesses, schools and churches are switching over to enjoy the reduced operating costs that come from these more efficient lamps.

In the 50 plus years since their inception, LED lighting has come a long way.  LEDs are capable of very long life, delivering high output with very low power consumption but they require a drive circuit to operate- that’s where the problem comes in.  To maintain high efficiency and long life, these switching drive circuits operate at higher and higher frequencies and maintain very high slew rates.  The result is unwanted emissions and an increase in Electromagnetic Interference (EMI).

While there are some bulbs that produce very low levels of interference, EMI mitigation typically increases the cost to the consumer as it requires additional shielding and noise suppression circuits and components.  Of course lower cost units appear more attractive to consumers, and for that reason they seem to be the most prevalent. 

Here’s an example of how cheap LED lightbulbs can cause havoc to the operation of wireless mics.  In the first scan you can see the three wireless mics rising above the noise floor.

 

However when the normal indoor lighting (with LED bulbs) is turned on there is a dramatic increase of almost 15 dB in the noise floor and the signal from the wireless mics is drowned out.

 

 

So what can you do if this happens to you?  Well, replace the offending LED bulbs with FCC approved units.  But you better measure them first as there is a lot of misunderstanding about this rating by manufacturers.  In the US, the FCC regulates radio and wire communications for devices with conducted emission frequencies between 450 KHz and 30 MHz and radiated frequencies from 30 MHz to 960 MHz. Most fluorescent light systems and ballasts operate below these frequencies and are therefore not regulated.  But LED bulbs operate with much fasted power supplies.  Compliance, for the most part, is somewhat based on the honor system which requires the manufacturer to be knowledgable with proper test methods and rules.  Unfortunately the FCC usually only addresses problems after they have been widely reported or are directly impacting license holders like mobile phone operators or TV and radio stations.

We recommend testing for LED (and any other lighting issues) as a part of your normal setup procedures.   Run a scan with your wireless equipment turned off with all lighting turned off and then with it all turned on, both utility lighting and stage lighting.  Are you seeing a difference in the noise floor?  Oh yeah, and if your garage door opener's range has suddenly been reduced you might wanna check and see if you have installed an LED bulb in the garage.

Other helpful tools include bandpass filters to reduce noise in your wireless mic system and nearfield antennas like our Spolight to mitigate noise from third party interference.   Curious how those work?  Checkout the video below from the InfoComm show where we demonstrated how filtering and nearfield antennas can dramatically reduce noise and improve wireles system performance.

 

 

 

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