I have been using the SignaLinc 4-pin Plug-in-Coupler with my 220v dryer for last 4 years. It is bit expensive but does an excellent job. I have multiple computers, UPS systems, home theater and surge protectors plugged into the electrical system. In addition, I have a total of 30 x10 modules installed in the house. Never had a problem with signal levels.
http://www.smarthome.com/4826A/SignaLinc-4-Pin-Plug-in-Coupler-Repeater/p.aspx
One word of caution when using repeaters with the newer X10 "Soft Start" modules. The recommended interface for these modules (LM465, WS12a, WS467, etc) is the LM14a 2-Way Lamp Module. This interface uses X10 Extended Code Direct Dim commands (not the standard bright/dim).
Since Smarthome uses the older Preset Dim1, Dim2 protocol and
not Extended Codes for their units, it is
possible that their repeaters will not repeat the Extended Code LM14a commands. I say possible because I do not have one of the Signalinc coupler/repeaters to verify this.
Having just typed the above, I remembered my old Boosterlinc in the "spare parts box". I dug it out and tried it with the LM14a extended code commands. My Elk-ESM1 indicates that it is definitely amplifying the LM14a command (go figure).
Does anyone have a Signalinc repeater and a ESM1 that could perform the same test? It would be nice to get a definitive answer on whether the Signalinc can handle extended codes.
Thanks,
Boiler