In the USA, Hitec and Futaba use negative shift while JR and Airtronics use positive shift. Many of the most modern digital transmitters can be set to use either shift (programable shift) so they can be used with most any ppm receiver. A very good transmitter for someone who is quite sure they will be continuing in the hobby is the Hitec Optic6 with the spectra module, very little more money than the cheapest 4 channel units yet is 6 channel, can hold setting for up to 8 models , shift selectable and has many other bells and whistles you will like using and can be used with all current ppm receivers on any of the 72 MHZ channels.