The PRC-2 receiver is capable of both manual and auto frequency programming. 
Using manual frequency settings the user adjusts the two rotary switches on the side of the receiver to specific settings that matches the PTX-3 transmitter frequency settings.  The 1.6M switch is for “coarse” adjustment (1.6 MHz per click) and the100k switch is for “fine” adjustment (0.1 MHz per click). Setting both to zero (00) is the low frequency end of the block and setting both to F (FF) is the highest frequency end of the block.
Frequency charts for block 24, 25 and 26 are attached below to assist the user with the rotary switch settings for a specific frequency. 
To set up the PRC-2 to auto sense the available PTX-3 transmitter follow this procedure:
1.  Before operating a receiver, one or more IFB PTX-3 transmitters must be placed in XMIT mode, with each transmitter set to the desired frequency and connected to a proper antenna, audio source, and power source.  The transmitter frequency block must be the same as the receiver frequency block as marked on each unit. 2.  Position the receiver at a location within 20 to 100 feet of the transmitter or transmitters.  With the power ON, depress the knob until the LED starts rapidly blinking, then release the knob. 3.  The unit goes into program mode and does a scan/search. Previously programmed frequencies will be automatically skipped. When the unit stops on a new frequency audio from the transmitter will be heard in the earphone and the LED will stop blinking rapidly and will change to a slow blink mode.The unit is now waiting for an operator decision. You must now decide to either SKIP or STORE the frequency (step 4 or 5 below.) Switching the power to OFF without storing will delete the frequency. 4.  To SKIP the frequency, depress the knob briefly and the scan/search will resume. 5.  To STORE the frequency into a channel memory, depress the knob until the LED blinks the new channel number, then release the knob. The frequency is now stored in an open channel.   6.  The unit will continue scan/search for other frequencies.  To store more frequencies repeat steps 4 and 5 above. Up to 5 frequencies can be stored in memory channels. 7.  When all desired frequencies are stored switch the power to OFF for a few moments, then switch back to ON. The unit will default to the channel number set by the switches and resume normal operating mode.