Reducing RFI at Home From Lighting Fixtures?

amper asks: "I'm in the process of building a new home recording studio. When I originally moved into my new (very old) house, I decided that in the interests of conserving energy, I would replace most of the incandescent lighting fixtures or lamps in my home with fluorescent fixtures or compact fluorescent replacement lamps in those fixtures which could not easily be replaced. Unfortunately, these fixtures are creating a massive amount of radio frequency interference in my home. The worst culprits seem to be the dimmable fluorescent fixtures in my living room. Barring replacing all my fixtures and lamps with conventional incandescents, can anyone point me in the direction of alternatives? Is it possible that the decreasing quality of most home goods has led to a decreasing quality in fluorescent ballast systems that are much more noisy from an RFI standpoint? Some of these fluo's are so noisy, they even emit audible sound! It's gotten so bad that I can't even play an electric guitar without turning off all the non-incandescent lighting in my house, which pretty much limits me to playing and recording during daylight hours (when I'm supposed to be out making money)."

Comments

Focus on ground loops, not on RFI sources.

[hankwang]

I come from a physical laboratory where we have to measure small signals with an acceptably low noise despite the presence of laser flash lamps, or even high-voltage discharges in more or less open air. The best way to avoid RF interference is not to remove all RF sources, but to design the electronic circuits correctly.

The main thing that makes electronic circuits sensitive to noise is ground loops. Often, signals travel through cables that have two wires or a central wire with a shield surrounding it. Normally, equipment (whether it is an oscilloscope or consumer-grade audio equipment) has a common ground, which means that the neutral wire of each and every input and output is connected. If you have more than two pieces of equipment interconnected, it is likely that there are loops in the ground wire, for example the cable from mixer to some effect generator, and the wire back. All these loops acts as antennas that can pick up noise. Having shielded cables doesn't help because it is the shield, that acts as ground wire, that causes the problems.

The first and simple step is to have all wires bundled as close together as possible, such that the area inside the loops is as small as possible. The next step is to upgrade your equipment to stuff that has balanced inputs, with those big XLR connectors. Here the shields are really shields against RF interference, while the signal is carried by two wires inside the shielded cable. Balanced signals means roughly that the equipment measures the signals on the two signal wires completely independent from the ground.

Re:Focus on ground loops, not on RFI sources.

[rhild]

To expand on that, any RF noise that gets into the cable will appear in phase on both signal conductors, which will result in it being cancelled out in the input circuit of the device the cable is feeding, if the device has balanced inputs.

CMRR (Common Mode Rejection Ratio) is a measure of how well an input circuit cancels out this kind of noise. When looking at the specs for gear this is one of the important but often overlooked numbers to check out.

RFI Solutions

[Ed Almos]

As a radio ham I have similar problems, try the following.

1) You can get ferrite rings of various diameters. Try winding a couple of turns of the cord leading to the light through one of these rings. The ring should be as close as possible to the fixture.

2) Wire RF chokes in series with the fittings. These work in a similar way to the ferrite rings but are more effective.

3) It's possible to obtain capacitors that are rated for 110/220 volt operation. Have a look inside a PC power supply and you may see one, they are normally encased in yellow transparent epoxy. Wire one of these across the fitting.

And finally.........

4) Ask for help from the right people. Try and find either a local radio ham or (even better) a local ham club. These guys will be experts at fighting RFI and will help you out.

Ed Almos
Budapest, Hungary