I am not sure why the 9CHP would cost any more than the 9CAP, they are basically the same radio with the default program on the 9CHP set for heli. Someone will correct me if I am wrong on this.

If you are going to use a synthesized reciever, you don't necessarily need a synthesized transmitter. However, If you plan on changing channels on the receiver, then you would need to swap the frequency module for the transmitter or use the synthesized module. It really doesn't make sense to have just the synthesized receiver, without several frequency modules for the transmitter, hence the synthesized transmitter module.

[link]http://www.gpmd.com/cgi-bin/wgpinf100p?&I=FUTJ87**[/link]

DIFFERENCES BETWEEN 9CA AND 9CH TRANSMITTERS:
9CH has trainer and 2-position switches on top right
9CA has trainer and 2-position switches on top left
9CH has a smooth throttle transition
9CA has ratcheted throttle