Yes you need the same "Channel" (frequency) if you want one TX to operate both model.

A Receiver will cost you around $50...

A Hitech 3 channel system (with the correct servos, reciever and another transmitter...) is about $80.... You can get a Hitech 4ch or better system with the correct servos and receiver if you special order...

With 2 full systems on different channels... you can both fly at the same time. Follow the leader or tie on streamers and do "combat"... all kinds of stuff to do.

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In the reciever is a small silver thing with a tape flag on it. that is the "Crystal" Pull it out and the writing on the flag tells you which channel number it is... and what the frequency is. It slides right back in. (The reciever will not work without the crystal.)