Most racers have or are now making the switch to 2.4GHZ systems. These no longer require to change crystals(frequency). Different makes of 2.4GHZ transmitters and receivers IE KO, Spektrum, Futaba, etc are not compatible with each other. Also make sure that your servos and ESC's are compatible. Older servos will only work with old analogue 40mhz, 27mhz or 35mhz systems. An older servo will either not work with 2.4ghz, get hot very quickly or even stutter under use. However different makes of servos will work with different makes of receivers regardless.