The Smartenit Harmony uses the 2413U/S Insteon Modem (IM) as a powerline interface. Insteon products are out of production, and pre-owned units are expensive if they can be found at all. As an alternative, the XTB-232 has been modified to support the X10 subset of the IM protocol for those using the Smartenit Harmony for X10 systems. An existing XTB-232 can be converted to the XTB-XM with new firmware and a minor hardware modification for the higher baud rate. After the modification, it can be converted back to a XTB-232 just by swapping the microcontroller.
Many of you are familiar with the XTB and XTB-IIR X10 Transmit Boosters that have been available since 2006. Like the other XTB units, the XTB-XM outputs a much stronger signal than normal X10 transmitters. It can deliver over 20Vpp onto the powerline. When combined with a good tuned-circuit passive coupler like the XPCP, the XTB-XM located near the distribution panel can provide strong signals throughout an average home.
The XTB-XM is no longer available.