The XTBM displays X10 signal voltage, carrier frequency, and last decoded X10 command.  It also displays powerline noise, and will indicate various types of errors that plague X10 communication, including the ubiquitous "bad start code".  Signal and noise levels are displayed with 10mV resolution, but the units are not displayed to fit all the information onto the LCD.

Some installations contain a repeater, such as the X10 XPCR or XTB-IIR.  Unlike other signal meters, the XTBM contains a transmitter.  Whenever it is plugged into a receptacle, it will briefly check for a repeater, and display the signal voltage received back if one is active in the installation.  This feature allows signal levels to be quickly checked throughout a home by merely plugging the XTBM into each receptacle for just a few seconds.  Note that a nearby signal sucker or strong noise source might cause a self-test failure during the repeater check.

The XTBM will indicate the level of each X10 command that is decoded in the form Xx.xx (Vpp).  When a repeater is on line, the signal strength of the original transmission is flashed onto the LCD for a fraction of a second before it is replaced by the strength of the repeated signal.

The carrier frequency of valid X10 commands is displayed in the form Fxxx (KHz).  This should normally be near 120KHz.  The meter can sample the range from 100KHz to 140KHz.  Readings outside that range may be due to the signal not being strong enough to be accurately measured, or it may not completely fill the X10 sample window.  The frequency of sufficiently strong “in-band” background noise can also be displayed.  Any noise source near 120KHz should be tracked down and isolated with a filter.

The XTBM samples noise in three windows:  before, during, and after the X10 sample window.  It displays maximum noise seen in the latter two windows in the form N.xx (Vpp).  Noise before the zero crossing does not affect X10 communication reliability, but it is sampled to identify Insteon commands.

Insteon commands straddle the zero crossing.  The XTBM will try to identify them as being different from other background noise.  Since the XTBM does not decode the data, it is possible for sufficiently strong "in-band" noise straddling the zero crossing to also be identified as an Insteon command.  The average level of noise mimicking an Insteon command is displayed in the form Ix.xx (Vpp).

The XTBM includes a noise alert system that can warn about a sudden increase in the background noise level.  When enabled, the XTBM will transmit “P1 ON” when the noise suddenly increases, and “P1 OFF” when it falls back to a safe level.  There is a slight delay so a momentary transient does not cause an alert.

Since the noise level may corrupt nearby X10 communication, this function is most useful with the monitoring device located remotely from the noise source.  If you suspect an intermittent noise source, plug the XTBM into the same circuit, and have the monitoring device on another circuit.

The noise alert system can be enabled or disabled by plugging the XTBM in while holding down the key of a manual controller sending “P ON” or “P OFF”.  The state of the noise alert system is briefly displayed whenever the unit is plugged in, and is non-volatile because it is stored in flash memory.

The XTBM should provide the information you need to efficiently troubleshoot your X10 system.

Decoded commands:

Status indications:

Full line messages:

Debugging with the XTBM

Inadequate signal strength and powerline noise often cause X10 reliability problems.  The XTBM makes it easy to identify “signal suckers” and major noise sources.  If the house has a repeater, just plugging in the XTBM will give a readout of the signal level at that receptacle.  Without a repeater, some signal source is necessary.  I recommend a TM751 or RR501 located on the same circuit as your main controller, and triggered with a PalmPad.  With the XTBM plugged into the receptacle under test, send a few commands, and the XTBM should display the signal amplitude and decode the commands.

X10 reliability begins to suffer at signal levels below 100mV.  If you have a circuit with low signal levels, the resolution of the XTBM should make it easy to identify the culprits.  Devices that cause a significant change in signal level when unplugged should be isolated with X10 filters.

Noise is also a major problem today.  It is possible for “in band” noise of only 50mV to cause serious reliability problems for X10 modules that do not have some form of AGC to raise their detection threshold above the background noise level.  Whenever the noise reads more than .02 or .03, or there is a series of ERR BSC readings, it is worth spending the time to track down and isolate the cause.  Move around the circuit looking for the highest noise level.  If that points toward the distribution panel, the noise source is likely on another circuit.  If the noise is higher moving away from the distribution panel, it is likely on the circuit you are testing.