Operating instructions

LOCAL OPERATION
3-39
Rx test (receiver testing)
Overview
The Communications Service Monitor 2948 has been designed to test the performance of mobile
communication equipment. This section explains the use of the Rx TEST mode. Typical uses
are:-
• Performance checking following manufacture
• Routine quality assurance testing
• Workshop or field fault diagnosis etc.
The dedicated Avionics SYSTEM function provides signals for testing ILS, VOR and SELCAL
receivers. The operation of the Avionics SYSTEM function is explained in Appendix B, Avionics
System.
The tests which need to be carried out will depend on the specification of the receiver and the
reason for testing, however a generalized list would be:-
Sensitivity
AF Bandwidth
AF Distortion
Selectivity
Blocking (or desensitization)
Spurious response
AGC response
With the Rx TEST mode selected, the screen and menu shown in fold out diagram (3-0) is
displayed.
From this screen and menu, the setting up of the inbuilt devices for receiver testing, and the read
out of results are carried out.
The sections of the monitor available for receiver testing are:-
RF signal generator
Audio modulation generators. Used to provide modulation of the RF generator
Audio tone generator. Provides tones for CTCSS, Sequential, DTMF systems
Audio distortion meter
Digital oscilloscope
As well as setting up the major sections of the Service Monitor, the following parameters are
selected from the
RECEIVER TEST screen:-
Audio filters
Pre-emphasis filtering
Selection of distortion measuring methods.