The Futaba 7CH transmits in either PCM or PPM regardless of the reciever it comes with. It's a setting withing the radio itself. If you have no use for the 8-channel receiver save the $40 and get the R127DF. If you're planning on putting it in the T-Rex you may want to forgo the receiver all together and just buy the radio (if possible, it was with my 9C) then get a Futaba R146iP PCM or R156F PPM mini receiver. They are smaller and lighter and a better choice for the T-Rex.