X10's RF products for N. America have long used LC tuning which has problems with drift due to temperature changes and as components age. Because of more stringent regulatory requirements, their European versions have had SAW resonators.
The HR12A has always had a silkscreen outline of a SAW resonator, the CM15A transmitter has a SAW resonator, and I've noticed that the MS18A schematic shows a SAW resonator.
I'm wondering how many of their previously LC controlled N. American transmitter models (e.g. motion sensors, door window sensors, keychain remotes, HR12A, etc.) now have SAW resonators. All of my models are several years old and use LC so I cannot check this myself.
The use of the narrow band RX3310A RF receiver in the CM15A and latest versions of the TM751 may have necessitated that they add better frequency control to the transmitters.
