The B-17 contains equipment for long and short-range two-way voice and code communication, intercommunication between crew members, emergency transmission, directional indication, and reception of marker beacon signals.
Interphone
The interphone system provides for communication between crew members. Command radio, liaison radio, and radio compass signals are audible over the interphone system at all crew stations. Any crew station can talk over the command transmitters. Only the pilot, copilot, navigator, and radio operator can transmit over the liaison radio.
Interphone equipment includes a dynamotor and amplifier located under the radio operator's table, and 12 jackboxes located throughout the airplane: 3 in the nose (for the navigator, bombardier, and forward gunner), 3 on the flight deck (for the pilot, copilot, and top turret gunner) , 2 in the radio compartment, 3 in the waist compartment, and one in the tail compartment.
Command Radio
The command radio is for short-range communication with aircraft and ground stations.
Voice transmission over the command set is available to all crew stations, but code transmission is limited to the pilot and copilot, who alone have a transmitting key. It is on the remote control box on the ceiling of the pilot's compartment.
The command radio consists of 3 receivers and 2 transmitters on the right forward bulkhead of the radio compartment. Remote controls are on ceiling of pilot's compartment.
Remote Control Units: The transmitter control box has an on-off toggle switch which turns on either transmitter, and a transmitter selector switch which selects either of the 2 transmitters. (Positions are provided for 4 transmitters, should the 2 extras be installed.) A wave selector switch turns on voice, CW (continuous wave) or tone as desired.
The receiver control is divided into 3 control units, one for each receiver. The low band receiver covers 190-550 Kc, the intermediate band from 3000 to 6000 Kc, and the high band from 6000-9100 Kc. Each receiver control unit has 2 switches to operate it.
The A-B switch selects either jackbox or control unit. Use "A" if plugged into jackbox; use "B" if plugged directly into control unit. A tone selector switch which can select "TONE," "CW," or "MCW" should be turned to modulated CW with "A" and "MCW" on. Then you can tune to desired frequency by means of a small handle which turns a calibrated dial.
The reliable transmitting range of the command set is 25 miles or less. Under good atmospheric conditions greater range may be obtained.
RADIO COMPASS (SCR 269-G)
The radio compass is a multi-purpose receiver designed primarily as a navigational instrument.
The power for this set comes from the airplane's batteries and inverters. The various relays and switches operate on the direct current supply, and the receiver and motors for rotation of the loop operate on the inverters.
This set has 2 antennas: a sensing (whip), or non-directional antenna, and a loop, or directional antenna.
The radio compass is a multi-band receiver and, as installed in B-17 aircraft, may be remotely controlled from either of 2 identical control boxes. One of these boxes is above and between the pilot and copilot; the other directly above and slightly to the left of the receiver itself in the navigator's compartment.
LIAISON TRANSMITTER
This transmitter, on the aft bulkhead of the radio compartment, insures communication with aircraft in flight and ground stations over distances up to 3000 miles, depending on atmospheric conditions and method of transmission. The usual reliable distances are 250 miles on voice, 500 miles on tone and 750 miles on CW. Only 4 jackbox positions (radio operator, pilot, copilot and navigator) can transmit on the liaison set.
This set has 7 interchangeable turning units covering frequencies from 360-650 Kc and 1500-12,500 Kc, and including a low band from 200-500 Kc in some models. For tuning this set, see communication section of B-17 T.O.'s.
The liaison receiver on the radio operator's table covers a frequency range from 1500-18,000 Kc. It uses the same antenna as the transmitter: the skin of the airplane. This is connected to a throw switch on the left side wall. This switch can change over to the trailing antenna (also on left side wall). The trailing antenna is operated from a control box to the right of the change-over switch.