Re: XTB-II Options

["Jeff Volp" <JeffVolp@xxxxxxx>]

"Dan Lanciani" <ddl@danlan.*com> wrote in message
news:1335290@xxxxxxxxxxxxxxxxxxxxxx
> In article <xigeh.170378$Fi1.6598@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
"Jeff Volp" <JeffVolp@xxxxxxx> writes:
>
> | I am familiar with their unit.  As you know, the TW523 returns data to
the
> | host controller during the last 11 cycles of each X10 command.  When
> | enabled, that is when the XTB-II transmits repeated data to the
powerline.
> | So the boosted signal is transmitted bit-synchronous with the second
copy of
> | each normal X10 command.  I believe that is how most repeaters work.
> |
> | Because the 120KHz bursts are not phase-locked, this approach can result
in
> | destructive cancellation of that second copy on the original
transmitter's
> | circuit.  However, any receivers on that circuit should respond to the
> | unaltered first copy from that transmitter.  Since the XTB-II would
normally
> | be driving at the electrical distribution panel, its output would
override
> | the original transmitter's signal on all other circuits.
>
> This seems to be the unstated (except occasionally by me :) theory behind
> most repeaters.  Sometimes I wonder, though, how probable it would be to
> have a pathological case where the level heard by a particular receiver
> from a transmitter is below the receiver's threshold, the level it would
> hear from the repeater is above its threshold, but the difference between
> the two signals is again below its threshold.  Operation could then depend
> on the relative phase of the two free-running oscillators in the
transmitter
> and repeater, and that could lead to some head scratching--especially if
> the levels shift in and out of the pathological ranges as other parts of
> the network change.

I don't think that would happen.  Assuming the repeater is at the
distribution panel, then the signal from the remote transmitter must be
strong enough to get that far.  So receivers on its own circuit should have
sufficient signal to detect the first half of the message.  When the
repeater transmits during the second half of the message, it should dominate
at the distribution panel, and on all circuits other than the one feeding
the remote transmitter.  Some receivers on that circuit could get a
corrupted second half, but they should have already accepted the good first
half.

One case where this would not be true is when the "remote" transmitter is
very close to the distribution panel.  In this case, that transmitter signal
should be similar in strength on its own phase to the output of most common
repeaters, and the first half of its message should propagate through the
house just as well to devices on that phase.  The second half of the message
can be corrupted on the transmitter's phase due destructive cancellation,
but the repeater's output should be OK on the second phase.

Jeff