Re: Water heater eating X-10 signal

["Jeff Volp" <JeffVolp@xxxxxxx>]

"Dan Lanciani" <ddl@danlan.*com> wrote in message
news:1338636@xxxxxxxxxxxxxxxxxxxxxx
> In article <04YUh.314346$5j1.274986@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
> JeffVolp@xxxxxxx (Jeff Volp) writes:
>
> | 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.
>
> I'm not sure it's that simple.  The imbalance required depends on the
> strength of the signal at the receiver.  If it is already near the
> sensitivity
> threshold then a 50% imbalance could still be insufficient to avoid
> trouble.
> This is basically the generic carrier interference argument where if the
> signals are strong enough to begin with then even their difference is
> likely
> sufficient to operate a module.  It's why you typically don't see a
> carrier
> interference problem with multiple synchronized transmitters collocated at
> a
> receiver.  For a simple protocol, X10 can lead to some pretty complicated
> analysis...

I thought a bit more about this since my earlier post.  A 240V load should
be on its own circuit. There shouldn't be any "signal suckers" on that
circuit other than potentially the 240V load itself.  So the starting signal
will be the differential level at the panel.  In an installation with
balanced loads, a repeater would produce essentially the same signal level
on both legs.  So, that could present a problem for 240V loads if both
phases were driven in phase.

> | 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.
>
> I certainly can't see any downside, but then I don't have any 240V
> receivers.
> Possibly the repeater designers know something we don't.  I suppose if I
> were building a repeater product I'd be tempted to make it a switchable
> option.
> There's something unaesthetic about driving what amounts to a differential
> line pair in phase and hoping for random impairments to make it work. :)

The differential line pair only refers to driving a 240V load, which you
agree is rare.  I think the better approach is to provide best performance
for normal 120V loads, which are probably over 99% of X10 devices.  I don't
like the possiblity of a 240V resistive load possbily causing havoc with
signal levels.  If the installaton does include a 240V load that has a
problem with signal levels, it could be addressed by placing a .1uF
capacitor to neutral on one of the hot leads to imbalance the signal levels.

> | 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.
>
> It depends.  What if the sensitivity of the 240V module is 100mV, it is
> currently seeing 100mV on one leg and 0V on the other, and the passive
> coupler causes 50mV to appear on the previously-0V leg?

Yes, it does depend on the loads on the other phase.  However, with a
reactive impedance of 13 ohms, there should be significant signal drop from
one leg to the other in a normal installation.  With no other "signal
suckers" in the path to the 240V load, the only thing to contend with is the
signal loss in the cable run itself.

> I keep meaning to check whether the official passive coupler flips the
> phase.  It uses transformers on both sides so it certainly could.  My
> brief experience with it was quite negative with previously working
> transmitter/receiver pairs failing once the coupler was switched in.
> Something funny was going on and since there was already significant
> passive coupling I wonder if it was somehow producing cancellation.
> Of course, this was at a time when I was lucky to have 50mV levels
> at some locations.

That was an easy test to do - just confirmed an old Leviton 6299 does flip
the phases.  Interesting is that its peak coupling is at 134KHz.

> | 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.
>
> I have the original (two black wires and one white; does not support
> extended codes).  There was a second rev that supported extended codes
> and could drive a third phase but had an absurd power-on sequence
> requirement.  They were both the same part number, right?

My two have two blacks, a white and a red.  So that must be the newer 6201.
I'll test it after I get a couple more XTB-IIs assembled.

Jeff