“Aircraft Radios” from Navigators’ Information File, Headquarters U.S. Army Air Forces, U.S. War Department, 1944:
AIRCRAFT RADIOS
Besides the radio compass there are three other radio sets in tactical aircraft with which you must become familiar.
1. Command set
2. Interphone system
3. Liaison set
Know where this equipment is located in your airplane. Know how to operate it. Most important of all, know which set to use for any given situation.
Command Set
The command radio set is controlled from the pilot’s compartment. Use it for communication from plane-to-plane or from plane-to-ground over limited distances. It consists of three receivers which operate on 3 to 6 megacycles, 6 to 9.1 megacycles and 190 to 550 kilocycles respectively. To obtain clear definition of range signals, place the switch of the radio range filter in the pilot’s compartment to “RANGE.” With the switch in this position, voice reception is nearly eliminated. With the switch on “VOICE,” the range signals give way to clear voice reception. Place the switch on “BOTH” to hear both range and voice signals at the same time.
Two to four transmitters are included which allow you to operate on predetermined frequencies. You can operate on only one transmitter at a time. Select the transmitter you want by turning on the proper switch.
To transmit code signals place the “TONE-CW-VOICE” switch on either “TONE” or “CW.” Use either the microphone button, a standard transmitting key, or a key located on the top of the transmitter control box.
Interphone System
Use the interphone system to carry on communication with the crew members in the airplane. The jackbox of the interphone system also provides means of switching your microphone and headset to the input and output circuits of other radio equipment in the airplane such as; Radio Compass, Liaison or VHF radio set and Command radio set.
To call another crew member on the interphone hold the jackbox switch in “CALL” position and simultaneously depress the microphone switch while talking. After calling, return the switch to “INTER” position and wait for an answer. To answer, the called party switches to “INTER”.
To use the interphone most efficiently, hold the microphone directly in front of your mouth, lips lightly touching the center of the mouthpiece. When you use the throat microphone, have the buttons face in against the sides of your Adam’s apple. Speak slowly and distinctly in a moderate voice.
Have the openings in the earphones directly over your ears and adjust the earphones so that the cups fit firmly and evenly to seal out noise.
Do not hold the microphone switch depressed when listening, for this affects transmission.
Liaison Set
The liaison radio set is capable of transmitting and receiving over a wide range of frequencies. Use it for long distance air-to-ground communication.
The receiver unit is capable of Voice or Code (CW) reception on frequency bands ranging from 200 to 300 kilocycles, 1.5 to 3.5 megacycles, 3.5 to 6 megacycles, 6 to 9.5 megacycles, 9.5 to 13.5 megacycles and 13.5 to 18 megacycles. You can pick up the Bureau of Standards Time Signal from Station WWV on this set at either 5, 10, or 15 megacycles. See Time Signals, NIF 2-25-1.
To receive voice signals:
1. Turn “AVC-OFF-MVC” switch to “AVC.”
2. Turn the volume control clockwise until you get a signal that you can hear easily.
3. Select frequency band desired by turning the band switch.
4. Adjust to the exact frequency by turning the tuning crank. Rock the crank back and forth slightly to obtain best definition of the signal.
To receive code signals:
1. Turn “AVC-OFF-MVC” switch to “MVC.”
2. Place “CW-OSC” switch to “ON” position.
3. Turn “CRYSTAL IN-OUT” switch to “IN” position after “CW” signal has been tuned in.
4. Adjust “BEAT FREQ” control to obtain a tone that is pleasing to your ear.
To listen to the “LIAISON” radio set, place the selector switch on the jackbox at “LIAISON”.
Transmission over the liaison set is the radio operator’s duty so only attempt it after he has given you proper instruction.
Know the operation, capacities, and limitations of each piece of equipment.
