The AN/ARC-4 (WE 233) provided four crystal-controlled channels from 140 to 144 MHz.  The RT-19/ARC-4 was supplied from the factory with four standard channels:

Channel 1 (Plane to Plane)      140.58 MHz  (Guard)

Channel 2 (Plane to Ground)   142.02 MHz

Channel 3 (Plane to Ground)   142.56 MHz

Channel 4 (Plane to Ground)   142.74 MHz

Crystal sets for other frequencies were available.

The SCR-522-A provided four crystal-controlled channels from 100 to 156 MHz.

Mike / KK5F