Wireless LED RF wash- Heads Up

[JD]

Brought in a bunch of Sennheisers for our upcoming passion play on Easter. They were mostly A band, tuned in the 540-560 region. Switched on the rack and the RF level meters were pretty much all pegged! (35Db) Tuned them down in the 518-530 region and found their happy spots. Still seeing 5 to 10Db RF noise, but no problem squelching that out. Bottom line, the source was the LED house lights. When I killed them, pretty much everything dropped to zero. (btw- there was also a bulge of noise in the 600 band on the B receivers.) There is about 3300 watts of LED lamps in the room, all white running off a dimmer as compared to DMX. Mix of brands. Biggest offenders were Philips lamps (A21, 11 to 12 watts.)

I thought I would post this simply as a heads-up that some LED or LED/Dimmer combos can play havoc with analog wireless.

 

[FMEng]

Welcome to the future. A variety of devices are polluting our RF spectrum, and the FCC can't be bothered to enforce its own rules. AM radio is almost dead due to noise in the band. FM, TV, and other uses of VHF and UHF will be useless in a few years. Maybe when police and fire agencies cannot communicate, it might get their attention, but it might take decades to undo the damage.

 

[RickR]

I thought I would post this simply as a heads-up that some LED or LED/Dimmer combos can play havoc with analog wireless.

Some fluorescent ballasts emit a lot of RF as well, but you don't see them in many theaters other than Caf-a-Gym-a-toriums. I've also seen fluorescents interfere with IR.

 

[JD]

Yea, not many transformer ballasts around anymore.
Kind of disgusting how much noise they are allowed to put out (or not allowed.) Both the fluorescent and LED supplies use switch-mode supplies operating in the 100+Khz range. Surprising to find so many harmonics in the 500+Mhz range, but I guess square waves will be square waves!

 

[Dionysus]

Yes it really is nasty how much RF pollution there is out there. I am NOT a big fan of the Philips retrofit LEDs, I've found another brand that is cheaper and much better. They aren't terrible or anything but they aren't the best either. They put out a fair amount of heat and have difficulty dissipating it, and as you said put out some nasty interference.
I'd also be curious as to what dimmers are dimming the LEDs.

 

[JD]

Old "Hub" architectural system (18 3.6k dimmers.) Pretty good size chokes, all wiring is conduit. Appears to be direct radiance from the lamps. We have TCP, Cree and Philips. The TCP and Cree do not appear to contribute much, but any circuit with the Phillips really puts out. I would drag a scope up there and look at the back-feed at the rack, but it's a 30 vertical climb up a rung latter in a coat closet sized shaft. (And yes, you read the 65Kw dimmer rating correctly! It used to have about 36k on incandescent on it before the LED conversion.)