# Help with RF interference

I run an animated Christmas light show on the house, and that interferes with my garage door opener whenever the lighting electronics are on. The lights themselves don't have to be on, the problem occurs when there's data on the wire. The neighbors don't have any interference problems so it's pretty local to my house. The receiving antenna on the opener is the factory original piece of wire. I understand basic electronics and am good with a soldering iron, but I don't know much about RF.

Other: I built a quarter wave ground plane antenna for an FM transmitter and don't seem to have any interference problems in either direction. No problems pulling TV off-air either (US ATSC).

The opener runs at 372MHz and the data rate on the LEDs is adjustable on the controller and tends to work best at 800-900kHz.

My thought is to build a receiving antenna for the opener that favors 372MHz and then a bandpass circuit to reduce the noise. I've looked at various antenna designs and can find online calculators for element lengths, etc, but I really don't know which antenna design I need, nor do I know the bandpass circuit I'd need. Any ideas?

Thanks.

EDIT: It's not very clear above, but the lights are completely hard-wired, not wireless.

This is not a case of in-band interference, because 372 MHz is of course three orders of magnitude higher than 800 kHz (and there will be no significant harmonics that high, even on a digital signal). Therefore, I do not expect that putting more band filtering on the receiver will help all that much.

If you want to try anyway, the simplest thing in that area is to use a shortened antenna — one which contains, or is entirely, a coil. (This is a high Q antenna, one with a small relative bandwidth.) You'll need to make a friend who owns an antenna analyzer or dip-meter to get it tuned spot on, but given that it shouldn't be hard.

An alternative explanation is that the LED control signals are getting into the receiver circuit after the RF tuned part and upsetting it — either by radiation or through the power cable. Ideally, you'd quiet down the LEDs by shielding and ferrites on the data lines, but of course that would block the light from the LED strips since the data runs through them! (I'm assuming you're using the popular modern individually-addressable LED strips, since you mention things like adjusting the data rate.)

So, maybe try putting ferrites on the power cord to the opener, and foil tape on any cracks or non-metallic parts of the housing that aren't where the antenna is. Lots has been written on how to buy and use ferrite toroids, and I am not an expert in the area, so I can only say “read about it”.

A cheap (~$20-$40) investment in measurement tools you might be interested in is getting an RTL-SDR device. You can plug it into your laptop or phone, tune to 372 MHz, and watch what effect your LEDs have (or don't) on that part of the spectrum. (Make sure the AGC is turned off!) This will tell you whether filtering the receive antenna will be useful. You can also use them to listen to FM radio, hams, airplanes, weather radio, and some emergency services radio.

• Thank you very much! I suspect you're right about signals getting in after the RF. There's a large gap in the case where the motor parks (discontinued Wayne-Dalton I-Drive). It also uses a PC power cable and I can probably find one around her with ferrites already installed. Your assumption on the LEDs is correct, though I'm using the individual bulb style, it's the same tech -- WS2811. ... and the RTL-SDR is on it's way ... – Marc Young Oct 19 '15 at 3:59

You might be getting RF through the AC lines. Shorten the length of your wires (where possible) and if you have a long length of wire to the socket, coil it up to form a choke.