As first reported here several weeks ago, it appears that the X10 RR501 does not maintain correct registration of its 3-phase bursts. At that time it was just a curiosity, but it has now become a problem when using a gated AGC sample window.
The region just before the zero crossing should be a good place to sample background noise to adjust the X10 sample threshold level. Insteon uses that region, but there should be no X10 transmission there. However, two different RR501 transceivers - Powerhouse and Leviton purchased years apart - occasionally shift their third phase burst into that slot. I captured a scope trace showing that:The scope was line-triggered with zero crossings at dead center, and 8.3 mS on either side. This trace shows the misaligned 3rd phase burst ending only half a millisecond before the next zero crossing. (The bright portion of the trace caught the scope beam writing the phosphor while the camera shutter was open.) Interesting, and possibly related is the missing 3rd phase burst from a prior sweep on the right half of the screen. The rightmost burst is at the next zero crossing.
A Google search has not uncovered this being reported before, and I wonder if anyone else has seen it. Since this occurs on two different units purchased years apart, there may be a gazillion units out there that exhibit this phenomenon. However, since the zero crossing burst IS correctly aligned, perhaps it has never been pursued before.