You can try doing a range-check with a friend.
Just let him hold the CX2 and you walk away while moving the servo's. You can spin it up as well, but thats dangerous for your friend .
Let him call you on your cell when the servo's stop moving and you still are putting in signals .

On my DX7 there's a range-check button, and than it turns down the transmitpower.
Be sure to keep your TX battery voltage over 5v!! Because when it goes bellow 5v signal will drop and when voltage reaches 4.5v transmision will stop completely!