X10 Interference from the Cellet Cellphone Charger

["Jeff Volp" <JeffVolp@xxxxxxx>]

The Cellet cellphone charger arrived today, and I tested it on a "private"
circuit with a XTB-IIR.  This is clearly a very nasty device for X10
communication.  I made my measurements at the XTB-IIR input bandpass filter
before the active gain stage.  That is a convenient place because all 60Hz
has been removed.  There is some "in band" gain due to the filter, so my
numbers are probably about double what would be seen directly on the
powerline.

When loaded to about half its rating, I measured bursts of 125KHz exceeding
1Vpp immediately after the zero crossing.  That is exactly where X10 signals
are transmitted.  Under load, the bursts are constant.  Unloaded, the bursts
are random, and can appear at other points in the waveform too.  The
frequency remains around 125KHz.

The XTB-IIR AGC totally rejected the noise from the unit under load, but
occasional "1" bits were detected when the unit was unloaded.  I never saw
the XTB-IIR respond to the noise as a valid X10 signal.  However, it is
interesting that the ESM1 gave a solid a "Good" indication when the unit was
under load.

I can certainly see how this charger will block X10 communication if the X10
modules do not incorporate AGC.  I'll do some more testing, and will add a
report on the X10 Troubleshooting page when I get the chance.

Jeff