Be careful on using the Spectra on the 3PK's. I have switch to 3PK from 3PJ because of the ease of use in settings and figuring out that the Spectra works. It sure does work but the servo' exhibit a shaking movement in neutral position that does not occur in the 3PJ, I have 2 spectras and they both do the same. Now I'm back using the 3PJ until I get enough Crystals to use on the regular module. The 3pk is good when you want ease in settings and use of digital servos.
Oh yah, these are all base on a non-digital servo/receiver setup.