Good question. Actually I have that situation here all the time. When I'm testing XTBs in my lab, my "home" XTB-IIR does participate too. Since the
120KHz is created locally at each transmitter, the frequencies will differ slightly. The actual voltage at any given point is the vector sum of both signals. The original transmitter will obviously dominate the local circuit. Since the XTB-IIR should have the lowest impedance coupling to the distribution panel, its signal should dominate for the remainder of the home.
For the techies out there - it is feasible for null points to exist where the two signals will exactly cancel. However, that would mean both signals are identically strong at that point, and are exactly opposite in 120KHz phase throughout the transmission window. Should such a situation occur, remember the first half of the X10 signal is not repeated. That would be the same strength as that received from the XTB-IIR at that node, and the receiving module should have no trouble responding to that first half of the command.
I hooked up the Monterey PLSA behind an AF120 15A filter and got some interesting readings. The WGL received an RF command and put it through a TW523 onto the house wiring. The Monterey showed normal commands being received (at .15 volts, even behind the filter!) with one exception: The display showed them all in lower case, which means it only saw the second, repeated half of the command. That makes perfect sense. The II is stronger than the original XTB and the XTB/TW523 combo was on another circuit. Only the repeated signal could punch through the filter, as would be expected.
The next test is to see whether the WGL's TW-523 alone gives the same readings. If it's higher without the XTB, then there's cancellation going on. If it's higher *with* the XTB then the two signals are combining. IIRC, the IIR alone can't punch through the AF120. The fact that is does so when it's amplifying an already boosted signal from the XTB seems to indicate that the end voltage of an XTB that's repeated by the XTB-IIR is considerably higher than either unit alone.
I tried doing some "signal dissect" runs where the Monterey looks at each of the 22 cycles and records 0's and 1's and their voltage during each cycle and that gave me information that seems to imply cancellation is occurring.
Now that I've transcribed that lengthy list two things seem to jump out. First, the noise level is very low, probably the result of the Monterey sitting behind the AF120 filter. The second is that the repeated frame is seems to be actually weaker than the first copy of the X-10 command.
Obviously I need to run more tests with both the XTB and the XTB-IIR but it looks like we're seeing some fade in the voltage as the command progresses. Looks fairly linear, too.
I didn't expect there to be any trouble. I've been operating a number of ControlLinc Maxi's, MiniTimers and TW523's through XTB's and then through the XTB-IIR that's installed at the circuit breaker panel without any noticeable problems. The very faint X-10 signal noise I can hear if a chime module's plugged in too close to the XTB isn't really a problem - it makes me wonder if the human brain could distinguish the different commands if they were a little louder.
Anyway, I'll take some more measurements when I get a chance. The next thing I want to see is whether the XTB-IIR can punch a signal through the AF120 when it's not boosting an XTB signal.
Since the XTB-IIR power supply is not regulated, it will droop as the transmitter is pulling current from the 4700uF energy storage capacitor. (The TW523 has 470uF.)
Measurements here show about 5% droop over a single transmission. (You can see that in the Hometoys workbench photo.) The droop does depend on how nasty a load is being driven. More current will be pulled from the supply when driving a heavy load, which will cause more droop. Sustained transmission into a 4.8 ohm resistive load will result in about 30% droop (and a very hot load resistor.) The version 1.2 board supports a full-wave bridge power supply, which has slightly better regulation. The total energy delivered is about the same, but there is less change in burst amplitude over the transmission. That was first incorporated into the 3-phase unit, but it will be ported over to 2-phase unit when the new transformers arrive.
While I?m not quite sure how the measurements were made, I suspect that you had a XTB driving the same phase that the Monterey was monitoring. I would expect that to be a stronger signal than when the XTB-IIR is driving both phases, especially if the opposite phase contains more ?signal suckers?. In any case, that is a pretty respectable signal being punched through that filter.
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