TM  1-1520-240-10            3-2-1 SECTION  II.  COMMUNICATIONS 3-2-1.  Interphone System (C-6533/ARC). The  interphone  system  is  a  multi-station  intercommu- nication  and  radio  control  system  for  control  of  voice radio communication. It also monitors the output of navi- gation radio receivers and warning tones from IFF and radar warning sets. The basic components of the inter- phone system are six control panels (fig. 3-2-1). There is one panel each for the pilot, copilot, troop commander, the  gunners  stations,  and  flight  engineer.  in  addition, there is an interphone station for the hoist operator and two external interphone receptacles. Power for the sys- tem  is  supplied  by  the  DC  essential  bust  through  the COMM INTPH LH and COMM INTPH RH circuit break- ers on the No. 1 and No. 2 PDP. 3-2-2.  Controls  and  Function,  Interphone  Control (C-6533/ARC).  (fig. 3-2-2) CONTROLS/ INDICATOR FUNCTION Function Selector Switch Position Five position rotary switch used to select interphone oper- ating mode. ICS Connects headset-microphone to interphone system. 1 Connects headset-microphone to No. 1 VHF FM or No. 1 VHF AM/FM radio set. 2 Connects headset–micro- phone to UHF radio set. 3 Connects headset-microphone to No. 2 VHF AM/FM radio set. 4 Connects headset-microphone to HF radio set. 5 Not used. NOTE Pilot/Copilot can transmit on all four transmit- ters. Troop Commander can transmit on the HF and VHF FM transmitters only. Gunners and Flight Engineer cannot access any trans- mitters. Receiver Switches 1-5, AUX, and NAV Position Seven two position toggle switches used to select-head- set audio input as follows: 1 - No. 1 VHF FM or No. 1 VHF AM/FM radio CONTROLS/ INDICATOR FUNCTION 2 - UHF radio 3 - No. 2 VHF AM/FM radio 4 - HF radio 5 - Not used AUX - VOR/Localizer NAV - direction finder OFF disables associated audio input to headset. ON radio enables associated input to headset. HOT MIKE Switch Position Two position toggle switch en- ables hands-free operation (PTT/foot switch operation not required) of headset micro- phone for interphone only. OFF Hands-free operation disabled. PTT/foot switch operation re- quired for operation. HOT MIKE Hands-fee operation enabled. NOTE Switch settings are not necessary to receive marker beacon, radar warning, and IFF audio tones. Press to talk (PTT) Switches Position Two or three position switches used to enable the microphone side of the interphone system when operator is speaking. These switches are described in detail below. Pilot/Copilot Trigger PTT Switch (on pi- lot and copilot cyclic stick) Position Three position PTT switch. Off disables microphone (not pressed) enables headset. Interphone (First detent) Enables microphone transmis- sion to all interphone stations, regardless of function switch settings. Radio transmit (Second detent) Enables microphone transmis- sion over radio set selected by control panel function switch. Pilot’s/Copilot’s Foot Switches (on cockpit floor next to heel slide) Position Two position PTT switch.