flight packs
As JWN said never try to use a DC crystal in a SC Rx it won,t work. Additionaly always use the same brand as the unit. In other words with a Hitec DC Rx always use a Hitec DC crystal even though you are useing a JR Tx with a JR crystal. All crystals are not cut the same even though both are the same frequency. There is more involved than just the crystal in frequency determination.
Its real simple, Order your rx with the appropriate crystal (brand and DCor SC) on the same channel as your Tx.
There is one exception to this that I am aware of and that is the use of Hitec crystals in GWS Rx has been approved.
If you would care to say exactly what type RC aircraft that you are going to get into i.e. park flyer, electric, glow power etc. I could make some specific rx model recomendations that would be appropriate to the aircraft you have.
John