Re: Water heater eating X-10 signal

["Jeff Volp" <JeffVolp@xxxxxxx>]

"Dan Lanciani" <ddl@danlan.*com> wrote in message
news:1338634@xxxxxxxxxxxxxxxxxxxxxx
>
> The only repeater whose circuit I've traced (ACT CR230) drives them out
> of phase.  My understanding has always been that this is the standard
> practice in order to accommodate 240V modules which would otherwise have
> a difficult time seeing the signal.  I assume it is also the reason for
> the standard warning about using a repeater in conjunction with the
> blocker/coupler.  Have you ever encountered a repeater that drives the
> legs in phase (ignoring your own designs, of course :)?  I have the
> original Leviton unit (i.e., the one before the one before the current
> one) but I'm not sure it's worth the bother to take it apart and trace
> the circuit.

That's an interesting thought regarding 240V modules.  Of course, the
percentage of those is miniscule compared with 120V modules used on
split-phase systems.

Since most X10 modules work fine down to 100 mV, or even lower, it would
take almost perfectly balanced attenuation in both legs for in-phase signals
to null enough at the 240V device to cause a problem.  With the small
percentage of 240V devices in service, it would seem to make more sense to
use in-phase drive so 240V resistive loads would not attenuate the signal.
You are correct in your assumption that the XTB-II drives 120KHz in-phase to
both legs.  When I tested the XTB-II here, I measured 30Vpp on one leg, and
25Vpp on the other leg due to an imbalance in loading.  So, a 240V circuit
would start off with a 5Vpp differential signal at the panel.

The commonly used .1uF passive coupler will drive both legs in-phase, but
the second leg will always be lower in amplitude.  That again would provide
sufficient signal to a 240V module bridged across both legs.

I have a couple of the old Leviton 6201s kicking around.  If I get a chance,
I'll scope it to see what it does.

Jeff