HomeLink (Garage Door Opener) Temperature and Polarization

I am having very poor performance with the built-in garage door opener in a 2013 Prius v. The Prius works well with three other openers I have used it with. This new problem is with a newly constructed house with a metal garage door and ceramic tile (known to attenuate radio signals) on the surface. When it did not work well, I supplemented the radio control that is mounted on the garage door opener motor assembly with an aftermarket, HomeLink-compatible Topens HLR01, which operates at 315 MHz. The Prius HomeLink button has been programmed to match the remote from the Topens unit. The Prius operation is sometimes excellent, sometimes useless, and often nearly useless. The remote control that came with the Topens always works excellently.

One hypothesis is that the radio connection is marginal and the Prius does not provide as much power as the Topens remote. Once, I mounted the Topens receiver in the window to avoid the problems with the ceramic tile siding. It seemed to work well, but then sometimes it did not. Then a friend suggested that the polarization of my antenna (vertical on the Topens receiver) was incompatible with the Prius transmitter. Perhaps the reflection off the hood of the Prius makes its polarization horizontal. Changing the antenna orientation helped, but then it worked poorly later. The next hypothesis was that the window, with its modern low E coating, was attenuating RF signals, too, so I constructed a quality antenna that stuck out through the wall. It worked excellently until the next morning. This morning, I reprogrammed the Prius HomeLink button with a the Topens remote, while the Topens was cold. It worked excellently. The temperature was 45 F, typical of the mornings when it does not work well; in past experiments it works well in the 50s.

My best estimate at this time is that the Prius does not have good temperature stability of its HomeLink transmitter frequency. I am hoping someone on the list has something to say.