Repeaters, like the XTB-IIR, perform their magic by “hearing” the first command of the pair and transmitting at much higher power at the exact time the second pair of the command is being transmitted.

The XTB - Amplify and Repeat X-10

Bobby Green

The XTB - Amplify and Repeat any X-10 Signal

Author: Bobby Green

The XTB-IIR will amplify and repeat ANY X-10 signal that it is able to receive.  It can do this because most X-10 commands are sent in duplicate pairs.  Repeaters, like the XTB-IIR, perform their magic by “hearing” the first command of the pair and transmitting at much higher power at the exact time the second pair of the command is being transmitted.  They effectively overlay a much stronger copy of the signal directly “on top” of the original signal put on the power line by the transmitting device.  In this way, it’s able to kill two birds with one stone because it both amplifies the original transmission and then broadcasts it on both phases of the home wiring. 

At the beginning of 2006 I was one of many unhappy X-10 users. I starting using X-10 in the early 1980’s to remotely operate my darkroom lights.  The kit I bought at Radio Shack had a transceiver and a little four-channel belt clip transmitter.  I no longer had to feel around in total darkness for the wall light switch.   It was “way kewl.”

Over the years, I added more and more X-10 gear.  Controlling the darkroom lights was good, but controlling all the lights in the house was much, much better.  I can still remember the thrill of all the lights going off with a single button push.  As time passed, X-10 and others began to create an astounding variety of control options and improved modules.  I added more and more X-10 stuff.  I got Powermids to run my AV gear an X-10 mouse remote to control my PC from anywhere in the house.  An adapter allowed me to flash the house lights whenever an alarm was triggered.  Then came an X-10 smart sprinkler system, a few Robodogs and four X-10 dual floodlights.  By and large, things were working very well.  Little did I know that a very large and dark cloud loomed as the world of X-10 was about to meet its greatest threat: the SMPS or Switched Mode Power Supply. 

Nearly everyone owns at least one SMPS device by now, even though they may not know it.  They power everything from LCD displays to cell phones to computers.  Smaller, lighter and much more efficient than their iron-core transformer based brothers, these “wall warts” have literally taken over the world of AC to DC power supplies.  They first began to appear in devices that needed a lot of current like laser printers, uninterruptible power supplies and personal computers, but today you’ll find them powering most anything that requires low voltage DC to operate.

SMPS power supplies have a lot of advantages over the linear supplies that they are fast replacing. Size and weight savings are considerable.  You’ve probably noticed that your new phone or laptop charger can operate on either 110VAC or 220VAC without auxiliary transformers.  That’s because they have a much wider input voltage range than their linear counterparts. The amount of power loss and heat build-up can be minimized resulting in much higher efficiency.  Their high efficiency has led the EU to mandate all new power supplies be of the switched mode design.  These seemingly miraculous devices do have a dark side, though, and it has to do with some of the “tricks” of the SMPS design. 

Switched mode PSs get their name from the way they operate, switching current on and off, tens of thousands of times a second.  It’s this fast switching that can generate serious electromagnetic interference.  EMI creates problems for X-10 signals in two ways.  A noisy SMPS can “overwrite” the X-10 message by transmitting noise on the powerline at or near the same frequency that X-10 depends on, 120kHz.

The second problem for the X-10 signal arises, ironically, as a result of efforts to control the noise reaching the powerline.  Some power supply designers sought to suppress the switching noise by placing a filter capacitor directly across the AC power leads.  While this design inexpensively reduces significant noise from the SMPS, it creates what HA enthusiasts call an X-10 “signal sucker.”   These signal suckers often make it very difficult or impossible for the X-10 signal to reach its destination.  By the mid 1990s, I began to notice that some lights would turn on and off by X-10 only at certain times of day, and sometimes, not at all. 

To top it off, SMPSs, particularly when used in compact fluorescent bulbs, have another bad effect on X-10. Many X-10 modules have a feature called “local current sensing.” This feature is very useful since it allows a user to turn a device like a floor lamp on using its built-in switch. When you operate the local switch the module senses the change and turns the lamp on. With SMPS, the trickle current from the X-10 module's sensing circuit gradually charges up the SMPS power supply filter capacitor. The voltage eventually reaches the point where the SMPS’s chopper circuit will activate momentarily. That makes the module think the switch was turned on. It can also cause a brief flicker of compact fluorescent bulbs, which incorporate tiny SMPS hidden inside the bulb’s base. The cures for such problems are not very elegant, and involve either modifying the module or adding a small nightlight to the circuit to drain off the trickle current.

In total frustration I bought a $300 Monterey powerline analyzer to help me hunt down the source of my X-10 problems.  Then I bought a box of X-10 plug-in filters in an effort to place all the signal suckers I could find behind them to protect the rest of the home-wiring network.  As more and more PC’s and SMPS found their way into my house, X-10 became less and less reliable.  The filters helped, but it turned out that each X-10 transmitter itself is a wee bit of a signal sucker, and having dozens of transmitters, there was nothing more I could do except try a coupler or coupler repeater.  That experiment was an unmitigated disaster!  After a week of lockups, lockouts, broadcast storms and devices coming on whenever they pleased I removed it. 

I was stumped.  It looked as if I had no choice but to dump my entire investment in X-10, now well into the thousands of dollars.  I began to investigate the many new home automation protocols that were appearing on the market.  Some folks I knew were switching to Z-wave, Insteon or UPB.  The ever-decreasing reliability of my X-10 gear made it look as if I would have to switch, too. 

Choosing a replacement protocol wasn’t going to be easy because of two big problems.  The first was cost.  All of the new equipment was far more expensive than X-10 gear, often by a factor of ten.  The second, and more important reason was that none of the new competition offered even a tenth of the control options that X-10 did.  I was faced with the unenviable position of spending more to do less.  A lot more.  That’s when I saw a posting in a home automation newsgroup from a guy named Jeff Volp looking for X-10 users willing to beta test his new device, the XTB.

What is an XTB?  It’s almost like the mythical carburetor than runs on water.   If it were a rifle, you’d never miss.  If it were a cell phone, your calls would never be dropped.  If it were a power drill, you’d be able to punch through stainless steel ingots as if they were butter.  Jeff Volp’s contribution to “cleaning up” X-10’s act is a plug-in device with an 110VAC outlet mounted on the back.  Plug in any kind of X-10 transmitter and it will boost the output voltage up to 5 times that of stock X-10 gear and the overall power of the signal by 25 times.  For those using a centralized controller like HomeVision or Stargate, this means a great improvement in reliability.  In the world of X-10, it’s all about signal strength and XTB users have reported tremendous improvements in performance as a result of the stronger signal. 

The signal strength of the XTB versus that of a standard X-10 Maxicontroller. The screen is divided in 5 volt increments. The first pulse is from the both the XTB and the Maxicontroller, the next two pulses come from the Maxicontroller alone. The third, dim short pulse is a phantom image (30 year old scope, says Jeff!) The Maxi is a three phase device, hence the two pulses following the one that's combined with the 1st XTB pulse.

Jeff quickly improved upon the original XTB device with the XTB-II series that acts as a coupler, repeater, amplifier and signal enhancer.   The XTB-IIR , the latest addition to the family, boasts a digital input jack that allows it to emulate, and in some cases actually exceed, the capabilities of the X-10 powerline interface module, the TW-523.  The TW-523 (a.k.a. the X-10 Pro PCS05) is an X-10 unit with an RJ-11 jack on one end that allows digital equipment such as home automation, drapery and pool control hardware to interface to the home power lines and send and receive X-10 commands.

For anyone who’s ever wasted countless hours tracking down X-10 signal strength issues, the XTB is the obvious solution.  While there are other coupler repeaters on the market, none offers the powerful signal amplification feature or the input processing capability of the XTB-II series. 

The X-10 output from the XTB’s is so high that both the Monterey Signal Analyzer and the Elk ESM1 X-10 bar graph meter “pegged” out at their maximum levels (4V for the former, 5V for the latter).  Remarkably, they did so at a considerable electrical distance from the XTB, indicating that the originating signal was far greater than 5V. 

It was fairly easy to calculate the voltage based on extrapolation by comparing the voltage drop between point X and Y produced by a weak transmitter like the CM11A.  Repeating the same test with the XTB boosting the CM11A signal showed that the X-10 commands are put on the household wiring at 22 to 24V. If the CM11A clocked in at 50mV at a particular receptacle, adding the XTB boosted that reading to .25 volts, or about 5 times the original signal level.

I threw the XTB every curve I could think of, rummaging through my box of X-10 goodies for test candidates.  I tested the XTB against several flavors of transceivers, from the RR501 to the TM751 and even the Robodog.   If you’ve got more than one transmitter, you may need more than one XTB.  Or you might consider the more capable XTB-IIR.

The XTB-IIR will amplify and repeat ANY X-10 signal that it is able to receive.  It can do this because most X-10 commands are sent in duplicate pairs.  Repeaters, like the XTB-IIR, perform their magic by “hearing” the first command of the pair and transmitting at much higher power at the exact time the second pair of the command is being transmitted.  They effectively overlay a much stronger copy of the signal directly “on top” of the original signal put on the power line by the transmitting device.  In this way, it’s able to kill two birds with one stone because it both amplifies the original transmission and then broadcasts it on both phases of the home wiring. 

The downside of the XTB-IIR is that it needs access to both phases of the incoming 240VAC feed at the service panel to perform at their best.  Some people can get by with plugging the unit into an existing 240VAC outlet, if they have a free one, others may have to have a 240VAC outlet installed. 

Which device you decide to buy (or build – they come in extremely well-documented kit versions) will depend on your particular circumstances.  While you can’t plug a vacuum cleaner into that outlet, you can plug in a power strip and have the XTB amplify several devices (Jeff recommends no more than three but I’ve found that to be a very conservative estimate).  The XTB’s were tested here with a CM11A, a TM751, a TW523, an X-10 LCD mini-controller and a ControLinc Maxi-controller all plugged into the same outlet strip without any apparent issues. Other devices that were tested include the Leviton Decora HCPRF Plug-In All Housecode Transceiver, the X-10 mini timer (both LCD and LED models), X-10 mini-controllers, and the IR543 Infrared Mini-Controller.  All worked without incident.  Some of Jeff’s Ebay feedback comments below are a good indication of how effective the XTB’s are:

    03/06/07: Holy smokes!!!! anyone that uses X10 needs one of these…

    02/01/07: WONDERFUL !!!!!!!!!!!!!!!! What a great product .. Refreshing engineering

    01/08/07: Awesome X10 Booster! Very responsive to emails & great service.

Should you try building it in kit form or purchase it assembled? Since there are very small components packed into a relative small space, it’s a project best suited for those with better than average soldering skills. I showed the XTB to a friend, asking him if he could solder one for me.  His comment was “not like that – that’s perfect!”  He was floored by the how neatly Jeff had assembled the beta.  Since he assembles each unit by hand, each one is pretty much a soldering work of art. If there was a program called “This Old Circuit Board” Jeff would surely be one of the hosts.    

The XTB can be programmed with a number of special modes.  There are settings to guard against repeater “ping-ponging” as well as a mode to shutdown the repeater if there’s a “stuck” button.  Those with centralized home controllers like Stargate, HomeVision and the Ocelot can interact with the XTB-IIR as well.  This capability provides features like  allowing notification of “stuck buttons” as soon as they occur (great for troubleshooting purposes!) and changing modes programmatically. For more details, see the XTB-IIR Mode Options Document.

For current ordering and price information, see:

XTB Bare PCB                                    $12 postpaid in USA and Canada
XTB Complete Parts Kit                    $49 plus $8 shipping
XTB Assembled & Tested                 $80 plus $8 shipping

XTB-IIR Bare PCB, PIC & case      $49 plus $8 shipping
XTB-IIR Complete Parts Kit         $109 plus $9 shipping
XTB-IIR Assembled & Tested      $159 plus $9 shipping

(Prices are subject to change)

Bobby Green
My short bio is that I am a retired research fellow from a Pentagon "think tank" who bought his first X-10 module at Radio Shack 30 years(!) ago. Some of them are still in continuous operation and will likely outlive me.

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