The Electric Phase Problem
I gather that is a pretty common problem, especially in older houses. When electricty enters your house, it comes in on a single 240 volt line. This 240 volt line powers things that need a lot of electricty, like your washing machine and hot water heater. However, for everything else, the 240 volts needs to reduced to 120 volts. Standard practice is to split the 240 volt line into two 120 volts lines (2 phases).
The problem is that X10 sends signals over your powerlines, and making the jump from one phase to the other can degrade the signals enough that they don’t get through. If you have no problem getting X10 signals in one part of your house, but the signals don’t get through at all in other parts, you probably have this problem.
Luckily, it’s pretty easy to solve. You simply get a repeater or phase combiner. This device plugs into a standard 240 volt outlet (most have a pass-through for your dryer or other appliance), and when it detects an X10 signal on one phase, it mirrors the signal to the other phase, boosting it enough so that it can reach your module unharmed. My house dates back to about 1910, as does its electrical system (some of the wires are still wrapped in paper and held in place with porceline contacts), so I had to deal with a phase problem at first. Here’s the combiner/repeater I ended up using:
It echos signals from one phase to another, and it also boosts them, which improves reliability in general. After installing it, I was able to pick up X10 signals anywhere in my house, even on power strips and other notoriously bad areas. Even if you don’t have a phase problem, a combiner with amplification might be a good investerment. It was about 80 bucks. You can get a cheaper ($19) one that just does coupling here. The more expensive amplifier ones are here.