You still haven't provided any details so I don't know whether you are dealing with 120VAC/60Hz or 230VAC/50Hz mains.

Here are URLs to several datasheets, application notes, and schematics of some X-10 PLC interfaces. They show various techniques for coupling to the powerline. While some are for FSK and/or obsolete parts, the powerline interface details still apply to X-10 and ASK modulation.Anand Dhuru, who posts here, has designed PIC-based X-10 interfaces and may be willing to share details.