Operating instructions

LOCAL OPERATION
3-18
Tx test (transmitter 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 Tx TEST mode. Typical uses
are:-
• Performance checking following manufacture
• Routine quality assurance testing
• Workshop or field fault diagnosis etc.
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 transmitter and the
reason for testing, however a generalized list would be:-
Transmitter power
Transmitter frequency
RF distortion
Spurious outputs
Modulation characteristics
Modulation frequency response
Companding/limiting
Modulation distortion
This Service Monitor will perform all of the above tests.
With the Tx TEST mode selected, the screen and menu shown in fold out diagram (2-0) is
displayed.
Using this screen and menu, the Service Monitor is set up for transmitter testing, and the test
results displayed.
The sections of the monitor available for transmitter testing are:-
The AF generators, used to provide a modulating signal for the transmitter.
The audio tones generator. Used to provide sequential tones for POCSAG and DCS
systems.
The RF power meter.
The RF counter.
The modulation meter, to measure the depth of amplitude modulation or the deviation of
frequency modulation and to recover the modulating signal for other tests. The
demodulated output is fed to the audio amplifier, and can therefore be monitored on the
loudspeaker or on a headset connected to the accessory socket. The SSB option allows
Single Side Band modulation to be demodulated.
The oscilloscope, to examine the wave form of the demodulated signal.
As well as setting up the major sections of the Service Monitor, the following parameters are
selected from the
TRANSMITTER TEST screen:-
The
TRANSMITTER TEST screen allows setting of the following;
IF filter bandwidth.
AF filter pass-band.
De-emphasis filtering.
Distortion measurement methods.