X10 AGC and Insteon

["Jeff Volp" <JeffVolp@xxxxxxx>]

I'm working on adding AGC to the XTB-II TW523 emulation mode.  The XTB-II
fully error checks all incoming messages, and sufficient noise can cause
messages to be rejected.  Since the XTB-II can recognize X10 signals down to
the sub 10 mV region, continuous background noise can be a problem.

All X10 data is transmitted with its compliment.  Only half the sample
windows should contain a X10 signal burst (neglecting the 1110 start
pattern).  So a simple means of detecting noise is to look for pulses in
every sample window.  More than a couple of counts (caused by random
glitches) in every window would mean the presence of background noise, and
the sample threshold should be increased.

This appears to work well in an X10 environment.  However, Insteon
transmissions will cause a problem.  They appear as noise to X10 because
they appear in every X10 sample window.  Once the Insteon signal goes away,
the threshold will recover.  However, a low-level X10 command closely
following an Insteon command could be missed.

There are a couple of ways to deal with this, and I'd like your opinions.
One is to speed up the recovery rate so the threshold decreases more
rapidly.  Another is to sample for noise at a position other than where the
Insteon signal can appear.  Unfortunately, that means noise appearing in the
X10 sample window would be ignored.  Or, maybe this won't be a problem at
all, and can be ignored.  Comments?

Jeff