The questions below are being taken from emails received since the XTB was introduced.  Some were not exactly "frequently asked" as they only appeared once.  This list should be considered a supplement to the on-line documentation already available for the units themselves:

Can the XTB or XTB-II/R be used on a combined X10 / Insteon system?
Can the XTB-II/R be plugged into an ordinary 120V outlet?
Can the XTB-II/R be connected to a 240V dryer outlet?
Do the 240V labels refer to European use, and not the 240V across my two phases?
How do I connect the single-output 240V 50Hz unit?
How big is the XTB-II/R, and how can I mount it?
Should I remove the passive coupler now in my panel when installing the XTB-II/R?
Why do my dimmers flicker when the XTB or XTB-II/R is transmitting?
Can the XTB or XTB-II/R help with electrical noise problems?
Why does my XTB-II/R sometimes miss commands sent by a RR501?
Why doesn't the XTB-II/R digital port work as well as a real TW523?
The XTB-II LED only flashes when it is first plugged in.  Is it working?
I only need direct boost for my CM11A (or CM15A).  Why was the XTB-II discontinued?
Why doesn't the XTB-IIR work properly on my 3-phase system?
The XTBR looks the same as the XTB.  What is the difference?
Why does the XTBM display FAIL SELF TEST in certain receptacles?
Why does the XTBM display less than 110KHz for my XTBR (or XTB-IIR)?
Why does the XTBM indicate ^NOISE^ when the display has a low noise reading?
Why does the XTBM indicate HIGH NOISE when my XPCR is repeating a command?
Why doesn't the XTB-IIR repeat extended commands?

Can the XTB or XTB-II/R be used on a combined X10 / Insteon system?  Certainly!  Many X10 users found the reliability of the X10 portion of their system was deteriorating after adding more and more Insteon devices due to the loading effect from multiple Insteon transmitters.  The XTB and XTB-II/R output more than enough power counteract the additional loading from the Insteon devices.  It will probably be necessary to choose the alternate AGC sample point to prevent the Insteon signals from looking like noise to the XTB-II or XTB-IIR.  Otherwise, the XTB-II or XTB-IIR may exhibit a brief decrease in sensitivity to incoming signals immediately following each Insteon transmission.

Can the XTB-II/R be plugged into an ordinary 120V outlet?  Yes it can.  Just connect a standard power cord to "120V PHASE I PWR" and "NEUTRAL" on J2.  A good tuned-circuit phase coupler is still required near the distribution panel if X10 devices are used on both phases.  The closer the XTB-II/R is to the distribution panel, the stronger the signals will be throughout your home.

Can the XTB-II/R be connected to a 240V dryer outlet?  Yes it can, especially if the dryer outlet is relatively close to the main distribution panel.  However, the conductors in a standard dryer cable are too heavy to connect to the internal terminal strip.  Three or four conductor 16 or 18 gauge 300V power cable can be wired to a separate dryer plug that can be purchased at a home building center or an electrical supply store.  Be sure to purchase a plug whose prong alignment matches your receptacle.  If the dryer outlet is a long run from the main distribution panel, it would be better to try to locate the XTB-II/R closer to the panel.

Do the 240V labels refer to European use, and not the 240V across my two phases?  Yes, the same printed circuit board is used for both versions.  All the 240V labels are for the single-output 240V 50Hz international version.  That normally ships with two 3-pin terminal strips, and the N/C means no connection for the second phase output.

How do I connect the single-output 240V 50Hz unit?  The easiest way to connect this version is to cut a standard 240V extension cord in half, and connect the cut ends to the terminal strips inside the 240V XTB-II (or XTB-IIR).  The plug end connects to "240V 50HZ PWR" and "NEUTRAL" on J2; the receptacle end connects to "X10 BOOST IN" and "NEUTRAL" on J1.  Your 240V transmitter connects to the receptacle (if using direct X10 Boost), and the plug obviously goes into a wall outlet.  Strongest signals will be obtained using an outlet near the main distribution panel.  Good tuned-circuit passive couplers are still needed near the distribution panel for a multi-phase distribution system.

How big is the XTB-II/R, and how can I mount it?  All versions of the XTB-II use a custom machined version of the Polycase DC-44F.  The case is 4 5/8 inches square, and about 2 1/2 inches high.  Mounting flanges extend out 1/2 inch from the "connection" ends.  Be sure to leave room for your power cable coming out through the strain relief.

Should I remove the passive coupler now in my panel when installing the XTB-II/R?  There is no need for a coupling capacitor because the XTB-II/R has two series tuned circuits to provide cross-phase coupling if required.  Since the dual coupling networks in the XTB-II/R will drive both 120V busses in your panel with exactly the same signal, a passive coupling capacitor may be left across them.  The SmartHome 4816H SignaLinc can also be left similarly connected.  However, an X10 XPCP passive coupler (or Leviton 6299) should be removed because it normally inverts the phase of the 120KHz X10 signal burst, and the two devices would fight one another.  An active coupler or repeater should certainly be removed.

Why do my dimmers flicker when the XTB or XTB-II/R is transmitting?  The high amplitude XTB signals can cause the triacs in some dimmers to trigger prematurely, which may cause nearby dimmers to flash brighter during a transmission.  The XTB-IIR includes two mode options to address this situation.  One delays the X10 burst until there is sufficient voltage across the dimmer triac to desensitize it to the XTB signal.  The other mode option reduces the XTB-IIR output power by about a third.  Several people who reported this effect said delaying the X10 burst solved their problem.  A firmware update is available for the XTB-II to include the same mode options.  If the problem occurs with the simple XTB, it is usually confined to the one circuit the XTB is plugged into.  It may be possible to move that unit to another circuit that does not contain any dimmers.

Can the XTB or XTB-II/R help with electrical noise problems?  It depends on whether the receiving module can recognize the strong XTB signal above the background noise level.  Some X10 devices, such as the higher price Leviton switches, incorporate some form of AGC to raise the signal detection threshold above the background noise level. The XTB or XTB-IIR will certainly help when using those devices in noisy environments.  Modules without AGC can be rendered deaf by the background noise, and will ignore the stronger XTB or XTB-IIR signals. In cases like this, the only option is to reduce the noise level so the receiving module is no longer saturated by that signal.  Blocking the noise directly at the source is best, but it is also possible to use a custom signal sucker to attenuate broadband noise on a given circuit.  Even though that will also attenuate the X10 signal, the powerful signal from the XTB or XTB-IIR should be well above the noise level.  I had created a custom "signal sucker" for my testing.  It alone attenuates noise from my CFL test cluster by a factor of two.  However, the XPNR X10 Pro Noise Reducer had a negligible effect.  The custom signal sucker is very simple - merely a 1.0uF 400VDC capacitor in series with a 4.7 ohm ½ watt non-inductive resistor.  It presents a heavy 6-ohm load at the 120KHz X10 frequency.  That is too heavy a load for normal X10 transmitters, but the XTB or XTB-IIR should still produce adequate signal levels even when driving several of those loads.

Why does my XTB-II/R sometimes miss commands sent by a RR501?  The XTB-II/R normally samples the powerline for noise just before the zero crossing of the AC waveform.  That sample point should best match the noise environment in the X10 transmission window, which is just after the zero crossing.  During testing, it was found that sometimes the RR501 RF transceiver (and the virtually identical Leviton 6314) will misalign their 3-phase transmissions, using 50Hz timing.  Since the transmission window just after the zero crossing does not move, X10 operation is unaffected.  However, the third transmission burst can fall into the XTB-II/R AGC sample window.  Thinking that is a noise burst, the XTB-II/R would decrease its sensitivity, and the following data bit(s) could be ignored.  Units that exhibit this problem with the RR501 or similar RF transceivers should be set for the alternate AGC sample point, as defined in the XTB-II or XTB-IIR Mode Options document that was supplied with the unit.  While this characteristic has been seen on all versions of the RR501 tested here, it is not known what causes them to occasionally space their 3-phase transmissions for 50Hz.  The similar TM751 may also exhibit the same characteristic.

Why doesn't the XTB-II/R digital port work as well as a real TW523?  There are really several possibilities.  Noisy environments may cause its AGC to raise the detection threshold above weaker signals, or might result in rejected commands due to its comprehensive error detection.  However, because a number of Stargate owners reported this problem, I thought the cause was likely something more insidious than powerline noise.  Jeff Stein of JDS kindly lent me a Stargate motherboard to investigate this further.  It turned out that even though the XTB-II/R met the X10 interface requirement, it didn't quite match the output timing of an actual X10 TW523.  The Stargate apparently relies on that timing.  This was resolved by a firmware update to better match the actual TW523 output timing.  If you experience a problem using either the XTB-II or XTB-IIR with a Stargate, please contact me for a firmware update.

Several people using other controllers also reported their TW523 emulation did not work properly, but the unit worked fine when using a TW523 connected to the X10 Boost input.  The cause of this problem was eventually identified through detailed measurements made by Schelte Bron in the Netherlands.  We found that power transformers from different manufacturers can exhibit different phase shifts even though their other electrical and physical specifications are virtually identical.  The effect is most evident when the transformer is configured for 240V 50Hz operation, which cannot be thoroughly tested with the 60Hz power available here.  The slight difference in phase shift causes the zero crossing reference to occur too early, resulting in incorrect sampling of the data, and possible lost data bits.  What made this problem so difficult to identify is that the transformer used in the prototype (and most of the early units) produces ZCD timing well within the X10 spec.  All units assembled since the cause was identified have their ZCD reference sampled directly off the AC powerline input to match the actual TW523 timing.  A relatively simple modification can be made to those units that exhibit this problem.  If you need this modification done for you, please just send the unit back for an update.

The XTB-II LED only flashes when it is first plugged in.  Is it working?  Unlike the XTB-IIR LED, which monitors all powerline activity, The XTB-II LED only flashes when it is actually transmitting.  Also, the XTB-II must be set to the proper mode.  Since many people use it with a CM11A or CM15A, it defaults to the X10 Boost mode.  In that mode the LED will flash when boosting a transmission from a controller plugged into the X10 Input receptacle (or connected to J1 for the 240V 50Hz version).  It switches to the TW523 mode on the first transmission received through the digital I/O port.  The XTB-II includes a basic repeater that is only active when enabled in the TW523 mode (16 & 15 ON).  More information on how to do that can be found in the XTB-II Mode Options document that was supplied with the unit.  This is not necessary in the XTB-IIR, which has the repeater enabled by default.

I only need direct boost for my CM11A (or CM15A).  Why was the XTB-II discontinued?  It is true that the XTB-II was the most cost effective match for the CM11A or CM15A.  However, most people have opted for the Enhanced Repeater version for the small additional cost.  The main differences are that it doesn't "lock onto" the X10 boost input, and its 3-phase signal bursts are enabled only at the X10 transmission windows.  Even though the XTB-IIR includes features not needed when paired with the CM11A or CM15A, its additional capabilities are probably a wise choice for future growth.  If any issues are identified where the XTB-II would be better suited for a given application, it is possible to add a mode option to "dumb down" the XTB-IIR so it functions more like the XTB-II.

Why doesn't the XTB-IIR work properly on my 3-phase system?  There are two issues that can arise in 3-phase systems.  The XTB-IIR only "enables" 3-phase transmission.  Like the TW523, the XTB-IIR transmitter is directly controlled by the digital I/O and X10 Boost inputs.  Any controller attached to either of those inputs must also have 3-phase transmission enabled to generate a 3-phase output.  Also, since the XTB-IIR and XTB-III only have a single processing channel, it can only repeat commands from controllers on the same phase that is connected to its Phase I input.  If there are controllers on other phases, the repeater must be disabled to prevent corrupting the commands.  If there are commands that must be repeated on other phases, the work around is to build macros in the main controller to echo those commands back through the XTB-IIR.

The XTBR looks the same as the XTB.  What is the difference?  The XTBR does indeed look virtually identical to the XTB.  However, functionally they are significantly different.  The XTB only boosts signals received through its X10 Input AC receptacle.  The XTBR does that too, but it has a microcontroller to monitor and repeat valid X10 commands received over the powerline.  That microcontroller includes many of the features of its bigger brother, the XTB-IIR.  And, because it only transmits the zero crossing burst by default, its power output is higher than the simpler XTB.

Why does the XTBM display FAIL SELF TEST in certain receptacles?  The XTBM self-test verifies the signal amplitude and data pattern of its repeater check transmission.  It takes several seconds after the XTBM powers up for its digital filters to adjust to the background noise level at that receptacle.  Rather than make people wait for that process to complete, the XTBM performs its repeater check as soon as it powers up, using the default values that are pre-loaded into the digital filters.  That works well for most receptacles, but a significant noise source or severe signal sucker on the same circuit may cause the read back of the transmitted signal to be out of tolerance, resulting in the failure indication.  Loosening up the limits could prevent this, but that would result in the self-test checking just functionality, and not accuracy.  (Version 1.05 or higher only runs self-test on command to eliminate this problem.  An update is available for a nominal charge.)