ORIGINAL: Charlie P.
One thing you do have to watch is that servos have three leads - positive, negative and modulated signel input. Some drive the signal input with a positive modulation shift and some drive the signal input with a negative shift. The two don't play nice together and the receiver has to be designed to work one or the other. Futaba and HiTec, for instance, are compatable negative servos. JR and Airtronics both use positive shift; though JR makes servos in both modulations. Not sure about Spektrum but I believe I heard they are negative shift.
Charlie, I think you are confusing FM receivers positive/negative shift with servos
. The servo signal is a pulse width and is compatible amoung all modern servos. Any modern servo can be use with any modern receiver, AM, FM, or 2.4 ghz. The older Airtronics servos had the three wires in a different order but that was changed in the '90s so that it is now compatible with the other brands.
Bruce