X10 RR501 Burst Misalignment

["Jeff Volp" <JeffVolp@xxxxxxx>]

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:

http://jeffvolp.home.att.net/x10xmtbuf/rr501_misalignment.jpg

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.

Jeff