The JR “12X” transmitter came in two styles: the integral 12X, which doesn’t support modules, and the modular version 12XMV. The integral version was vastly more popular than the modular version. I’ve read that what looks like a module on the back of the integral version is only a lid to cover the hole where a module is on the 12XMV.

If the 2.4GHz antenna on your transmitter is on the top of the case where the collapsible antenna is on the 10X, you have the integral version. On the 12XMV, the 2.4 antenna is a part of the module, coming out of its back. The transmitter retains the collapsible antenna mount. The 12XMV DMS and PPM/PCM modules are unique to that transmitter. It can’t use modules made for previous JR transmitters.

Allan