User Guide

Series III Avionics
Pilot's Guide
Page 1
VCS-40A VHF Communication System
General Description
The Chelton VCS-40A VHF Communications System is a fully synthesized ATC VHF transceiver. The
VCS-40A system consists of a lightweight, remote-mounted VC-401B transceiver and a panel-mounted
CD-402B Control Display Unit.
The VC-401B transceiver is available with fixed 25 kHz channel spacing, fixed 8.33 kHz channel spacing
for European airspace, and switchable 25 kHz - 8.33 kHz channel spacing. Operation over the frequency
range of 118.00 – 136.975 MHz is standard. Extended operation over the frequency range of 118.00 –
151.975 MHz is available as an option.
The VC-401B features a coherent squelch system that permits the receiver to respond only to on-channel
signals, rejecting high-level noise. This makes it ideal for CLIMAX operations. The system also features
built-in SELCAL and ACARS capabilities for regional airlines and major fleet operators.
Reliability of the VC-401B is substantially increased by a specially designed thermal protective device that
enables continuous operation at reduced power (instead of the full 20 watts rated output) without
damaging the transceiver. A heavy-duty heat sink accommodates continuous operation, and a unique
cooling fin design dissipates heat, decreases internal unit temperatures and increases service life.
The CD-402B Control Display Unit is available in versions for use with transceivers with fixed channel
spacing (25 kHz or 8.33 kHz), and for units with switchable (25 kHz and 8.33 kHz) channel spacing.
The CD-402B Control Display Unit provides a simultaneous readout of two frequencies: The active
frequency in the upper display and, immediately below it, the standby frequency. Frequency switching is
accomplished by simply pressing a frequency transfer button. The Transmit Annunciator (Tx) appears in
the display when RF is present at the output of the transceiver, providing positive proof-of-operation.
When the VC-401B System is turned on, a diagnosis of all critical circuits begins, and continues until the
System is turned off. If a fault is detected at any time, a FAIL annunciation appears in the display.
The VCS-40A System has a nonvolatile memory which allows it to remember the last frequencies
displayed, indefinitely, even when power is removed. This feature prevents momentary power interrupts
from affecting the system, and allows the last frequencies used to appear immediately when the System
is turned on.
The VCS-40A System provides ARINC format 429 output for external use, and can also be tuned by
ARINC format 429 commands from external equipment such as an RMS-555 Radio Management
System.