The DCX is a dual conversion receiver, you have to use a dual conversion crystal. The MX3 crystal is single conversion. Just get the Hitec dual conversion crystal and you should be fine. The easier way to do it in the future is to get the Hitec HFS-03MM rx it is single conversion and works with all radios. You just have to use the TX brand of crystal so you could have plugged your Airtronics crystal in it and been set. I have a Hitec radio and use both receivers with it but even then you nhave to make sure you don't mis up the dual and single conversion crystals.