Receivers convert the radio frequeny received to a lower frequency (called the intermediate frequency or IF) before decoding the signal. I think the usual IF is 455kHz or thereabouts.

Dual conversion receivers carry out this frequency conversion twice, so there are two IF stages.

Reason for doing this is to increase the selectivity of the RX, ie to make it more immune to interference.

Some time since I did my radio theory, however I believe the above is correct

If not no doubt someone will jump in.

Terry