A single conversion receivers a cheaper smaller and lighter and are used in the park flyer type planes They do not have the long range capability of the more expensive receivers. These receivers have a single image frequency conversion and do not have as good adjacent channel rejection as the more expensive receivers

Dual conversion receivers have two image frequency conversion stages and have better adjacent channel rejection

To change the frequency of either type receiver requires only one crystal but a dual crystal cannot be used in a single conversion receiver and vice versa