Thanks for your comments; actually I did install one of those multi-vaned LED lights in my garage a while ago. I will take that out and see if it makes a difference.
I was getting a range of a 'half a block away', so it was doing that before, so whether Homelink was designed for that distance or not, it did it. The sudden loss of signal effectiveness suggests something new happening, either my LED light or a neighbor doing something nefarious.