The bottom side has all the RF circuitry -- the chip is a Nintendo chip marked "WR-DOL / H2102 / CG2710 / 02", presumably the radio.

EPCOS X6882 custom bandpass filter

Trim-pot for adjustment at the factory -- could be a frequency tweak or gain adjustment.

The rotary switch allows the user to choose a frequency to avoid interference with other devices.

The antenna is mounted directly on the PCB, inside the device.