LiftMaster Model 8155W - Electric Garage
Door Opener RFI
During the fall of 2019 we replaced our garage doors and decided to splurge and have electric garage door openers installed at the same time. Before moving ahead with a purchase, I asked around in several ham radio forums about whether the new garage door openers were resistant to RF ingress from amateur devices and was assured that the new digital systems were pretty much bulletproof. As it turned out, my two LiftMaster model 8155W units don't flinch at all when I transmit with full legal limit power levels from 160 meters through 10 meters. There are also no problems at all with my 100 watt signal on 6 meters or my 50 watts on 2 meters and the 440 MHz bands. I was very surprised that keying my 6m/2m/70cm mobile while parked under one of the LiftMaster units also doesn't trigger any kind of response. So, the control boards inside the LiftMaster units aren't disturbed by any of my station's emissions and my nightmares about my garage doors opening and closing every time I transmitted proved to be unfounded.
It would be nice if that was the end of the story, but unfortunately, when I tested the 160 meter band I was greeted with a storm of noise in the receiver that raised the noise floor on that band by as much as 25dB at the center of each pulsing peak which appeared every 20 kHz. Additionally, when I tuned down to the AM BCB it was also blanketed from top to bottom with broadband pulsing noise that obliterated strong signals on that band. In fact, every AM radio in the house was hearing the LiftMaster units when they were powered on, but the kitchen radio was affected the worst since it was only 15 feet away from the garage. A quick check of reception on 75 meters through 10 meters plus the VHF/UHF amateur bands showed that everything above the 160 meter band was perfectly clean. So... it was going to be necessary to filter noise egress from the LiftMaster units from 2.0 MHz and below. In the short term, I installed the ultimate stop filter, an ON/OFF switch to the AC mains feeding the garage door openers.
It looked like most of the noise was leaking out through the AC input of the LiftMaster units so I decided to start there. Fortunately, my neighbor (Dave - K1GQV) had a couple of Mix 31 torroid donuts left over from a project last summer and he passed them on to me. The Mix 31 ferrites are useful as cores for chokes that can block RF between 1 MHz to 300 MHz so they are a good choice for blocking noise on the 160 meter band that was passing into the AC line. I grabbed some unused AC cords that were left over from old computers and chopped off the ends that plug into the computer power supply. Then I passed the wire through the cores a dozen times and terminated the end of the cords with a 3-pin AC socket. They looked neat and would easily handle the maximum 6 amp draw of the LiftMaster units when they were moving the doors.
Fair-Rite Mix 31 Round
Cable Core available at Mouser: part# 623-2631803802
priced @ $4.89 each (October 2019)
When I installed the Mix 31 filters between the AC outlets and the LiftMaster units the noise on 160 meters was almost completely eliminated. In fact, it was only barely visible on the receiver's panadapter during the daytime when the band was empty and was definitely clean enough that it would not be heard at all in the evening. However, the AM BCB was still being obliterated, mostly at the low end of the band. I ended up buying two Mix 75 torroids from Palomar as their useful RF blocking range is from 150 kHz to 5 MHz. I had two cheap 3 wire extension cords from Walmart that were very flexible and so I cut 3 feet off one end of each cord and wound them ten times through the mix 75 torroids. I terminated the cut ends with a 3 pin AC socket.
.
Mix 75 cable core
available at Palomar Engineers: part# FT240-75
(RFI Range 150 kHz - 5.0 MHz) priced at $12.95 each
(October 2019)
I installed these filters in series with the Mix 31 filters and hoped that the overlap of coverage would be effective. As it turns out, the series filtering is extremely effective with the AM broadcast band now perfectly clean on every AM radio in the house and the 160 meter band shows no sign of any noise from the LiftMaster units. I had some Mix 31 split cores left over from another project so I ran 3 turns of the wire bundle for the safety sensors and the hard-wired up/down motor controls mounted on the wall through a Mix 31 split core. I don't think that was really necessary as I couldn't detect any noise on those wires but there's no harm in putting them inline. One of the filtered LiftMaster installations can be seen in the picture below.
My final thoughts on eliminating the noise produced by the LiftMaster model 8155W units:
1. If you don't listen to the AM broadcast band and have no interest in the 160 meter band it looks like these units are quiet on the 75 meter band and above without adding any filters.
2. If you don't listen to the AM broadcast band but 160 meters is important you can probably get satisfactory results on 160 meters by installing only the Mix 31 filters.
3. If you listen to the AM broadcast band and use 160 meters install series connected Mix 31 and Mix 75 filters on each unit. This produces the cleanest results across the MW/HF spectrum.
The short 35 second video below shows what the 160 meter band looked like with the LiftMaster units unplugged, then how the band looked with the unfiltered LiftMaster units powered up on standby, and finally how it looks now with the filters installed and the LiftMaster units powered up on standby. I don't know for certain what is causing this particular RFI problem, however, from what I have read there are garage door openers out there at this time that use PWM motor controllers. The implementation of PWM controllers in current HVAC systems has caused lots of noise for hams and it's certainly possible that my smooth-running LiftMaster units are using PWM motor controllers in the 8155W contractor-grade models installed here.