COBHAM FliteLine CVC-151 User Manual

CVC-151
VHF Communication System
Installation Manual
Section 2 – Installation
150-048100 Rev. H
Page 18
C. Dual Installation Considerations
(1) Reduction of cross radio interference by using Transmit Interlock feature.
All radio transceivers have a noise floor associated with the transmitted output signal. When two or
more radios are installed on the same aircraft, the transmitted noise floor can cause the squelch of a
radio operating in receive to open if care is not taken to maximize the isolation between the antennas
of the two systems. Isolation of greater than 35 dB between the antennas should be a system design
goal. However, due to the size of the aircraft or limited locations for antenna mounting, it may not be
possible to obtain optimal antenna isolation or location.
In non-optimal situations, to reduce squelch opening during radio transmission, a Transmit Interlock
function, pin 86, is available that reduces the sensitivity of the affected receiver when activated. The
input for this function is open collector logic. To enable this function, this pin should be pulled to
ground only during transmission of other radio systems.
On a two radio system the Transmit Interlock function can be implemented by the addition of two
lines connecting the desired push-to-talk (PTT) lines and the Transmit Interlock pins as follows:
CVC-151 System #1 CVC-151 System #2
P1001 P1001
PTTLOWMIC /_
, pin 80 to
INTERLOCKTX _
, pin 86
or
2PTTVOICE _
, pin 73 to
INTERLOCKTX _
, pin 86
and
INTERLOCKTX _
, pin 86 to
PTTLOWMIC /_
, pin 80
or
INTERLOCKTX _
, pin 86 to
2PTTVOICE _
, pin 73
It is important to notice that
PTTLOWMIC /_
is the audio return line as well as a PTT input for the radio.
This input is designed for carbon microphones that combine the microphone bias and the PTT function.
For systems that have an independent PTT line,
2PTTVOICE _
should be used to eliminate the
possibility of noise coupling into the audio.
For three (3) CVC-151 installations six external diodes can be used to interconnect the PTT inputs to the
Transmit Interlock inputs. The circuit for this interconnection is shown in Figure 2-1. In this figure pin 80
is used as the PTT input but pin 73 should be used if a separate PTT line is used.
The document reference is online, please check the correspondence between the online documentation and the printed version.

COBHAM FliteLine CVC-151 Specifications

General

Brand	COBHAM
Model	FliteLine CVC-151
Category	Conference System
Language	English