there are crystals for Rx & Tx, wrong way round & they won't work, there are also different frequencies, ie 40mhs, 27mhs 36mhs & 70 mhz. again a 40 mhz won't work in a 70 mhz radio. some brands (ie futaba) have crystal specific radios, so a JR crystal won't work properly in them. and also crystals have a shelf life, after a while they start to glitch, then die.