I have done some new experiments.
I decided to take the Powermid transmitter outside my apartment, and found that the LED glowed even brighter outside. I then drove it a few miles in each direction and got the same results consistantly. In my car I used an AC inverter to power it, but I also just plugged it into AC at various outdoor power sockets. The results were very consistant.
I took it over to a nearby office building and tried it at various points in the building. In the interior the LED was dark, but at points near the exterior or near windows it glowed.
In my aprartment there is no spot where the LED stays dark. It's a brick building constructed in the 1950's, which I presume has walls that provide less shielding than the the new office building.
I don't know if there is something special in my area transmitting at
418mhz, or if this is typical. My guess is that it's not that unusual, and that most people have better shielding. Even in my apartment the background LED glow does not cripple operation with most of my IR devices. I started into this because just one of my IR controlled devices would not work either through the Powermid, or even directly when the Powermid transmitter was on. Most of the others work but are intermittent at times.
Probably an unlucky device, poor shielding in the walls, and an unknown RF source painting the neighborhood.
I have tried a Terk a year back which operates at 433mhz and it was similarly balky. It was a short test, and at the time I didn't test for background glow outdoors. Either that background is over the whole
418-433 range, or these devices are not real discriminating by frequency.
I was going to try a URC-9910, but I see its also at 433 which is discouraging. (Also they seem to be in very short supply).
I really seem to be stuck. I wish someone would make an 802.11 device. That would allow generating the IR sequence from a laptop/pda as well as from a matched 802.11 repeater, and also work more reliably.