I bought a hitech 75mhz fm dcx and though I would try it out with my Fut 3pk and I set the 3pk to ppm fm and thought it should work, but I get gittery servo and no response did I buy a dud from tower or are they incompatable?

which x'tal are you using?

performace devices single conversion fut fm
and the stock futaba fm crystal that came with the 3pk

The DCX is dual conversion, you will need to use the Hitec dual conversion x'tals.