Re: X10 AGC and Insteon

[Joerg <notthisjoergsch@xxxxxxxxxxxxxxxxxxxxx>]

Hello Jeff,


> 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?
>

Doesn't Insteon use 131kHz? If that is the case you might consider a
120kHz LC filter with high enough Q to sufficiently suppress 131kHz but
not so high as to let X10 devices with sloppy alignment fall too far
down the slope.

Of course one could devise a steep elliptic bandpass that goes from
115-125kHz but that would probably be over the top here. One or too
loosely coupled LC should be fine. This will also greatly improve your
SNR except in cases where a switcher harmonic or other noise falls smack
onto 120kHz.

--
Regards, Joerg

http://www.analogconsultants.com