Very high frequency communication system General
The very high frequency (VHF) communication system supplies communication over line-of-sight distances. It gives communication between airplanes or between ground stations and airplanes.
Abbreviations and Acronyms
ACARS - aircraft communications addressing and reporting system
ACP - audio control panel
AM - amplitude modulation
ARINC - Aeronautical Radio Incorporated
BITE - built-in test equipment
comm - communication
EEC - electronic equipment compartment
FDAU - flight data acquisition unit
FDR - flight data recorder
freq - frequency
I/C - interphone communication
LCD - liquid crystal display
LED - light emitting diode
LRU - line replaceable unit
mic - microphone
MSEC - milli-second
PSEU - proximity switch electronics unit
PTT - push-to-talk
RCP - radio communication panel
REU - remote electronics unit
RF - radio frequency
R/T - receive/transmit
SELCAL - selective calling
sql - squelch
SSB - single side band
SSFDR - solid state flight data recorder
VHF - very high frequency
VSWR - voltage standing wave ratio
xmit - transmit
General
The VHF communication system supplies the flight crew with voice and data line-of-sight communication. The VHF communication system can be used to communicate between airplanes and between airplanes and ground stations.
The VHF communication radio is tunable in the frequency range of 118.000 MHz to 136.975 MHz. The VHF radio is used to transmit and receive voice and data communication.
System Components
The VHF communication system has these components:
Radio communication panel
VHF transceiver
VHF antenna.
The RCP supplies selected frequency signals to tune the VHF transceivers. You can use the RCP to select the frequency of any VHF communication radio.
The VHF transceiver transmit circuits modulate an RF carrier signal with voice or data audio. The receive circuits demodulate the received RF carrier signal to detect the audio from the RF carrier. The detected audio is used by the flight crew and other airplane systems.
The VHF antenna transmits and receives RF signals.
External Interface
The VHF communication system connects with these
components/systems:
Remote electronics unit (REU)
Proximity switch electronic unit (PSEU) выкл-ль сближения с землей
SELCAL decoder unit
Flight data acquisition unit (FDAU). Приобретение
System Operation
The control panel sends selected frequency signals to the transceiver. The audio control panel sends radio select signals and receive volume control to the REU.
During transmit, microphone audio and PTT signals go to the VHF transceiver through the REU. The transceiver uses the microphone audio to modulate an RF carrier signal made in the transceiver. The transceiver sends the modulated RF signal to the antenna for transmission to other airplanes and ground stations.
During transmit, the flight data acquisition unit receives a PTT signal from the transceiver. The flight data acquisition unit uses the PTT for key event marking to record the transmit event. During the receive operation, the antenna receives a modulated RF signal and sends it to the transceiver. The transceiver demodulates or removes the audio information from the RF carrier. The received audio goes from the VHF transceiver through the REU to the flight interphone speakers and headsets.
The SELCAL decoder unit receives audio from the VHF transceiver. The SELCAL decoder unit monitors the audio for SELCAL calls that come from the ground station.
The VHF transceiver receives an air/ground discrete from the PSEU (proximity switch electronics unit). The VHF transceiver uses the discrete to calculate flight legs for internal fault memory.
Flight Compartment
The radio communication panels are on the P8 aft electronic panel.
The audio control panels (ACPs) are part of the flight interphone system. The ACPs have an interface with the VHF communication system through the REU. The captain and first officer ACPs are on the P8 aft electronics panel. The first observer ACP is on the P5 aft overhead panel.
Electronic Equipment Compartment
VHF transceiver 1 is on the E1-3 shelf.
VHF transceiver 2 is on the E1-5 shelf.
VHF transceiver 3 is on the E3-3 shelf.
General
The VHF antennas are on the top and the bottom of the airplane fuselage on the centerline.
Power
The 28v dc standby bus supplies power to the VHF 1 transceiver and radio communication panel (RCP) 1.
VHF 1 Transceiver
The VHF 1 transceiver has an interface with these components: