There are a few BASIC things the TX and RX need to have in common.

1. BAND - They must be manufactured to operate in the same band area. 72 MHz, 53 MHz, 27 MHz, HAM band or what ever. Don't cross.
2. Channel - Crystal or module determined. In US only RX crystal can be operator changed but he can change TX modules. Other countries have their own rules.
3. Modulation - AM, Regular FM or PCM
4. Shift