Operating instructions
OPERATING MANUAL 2945A
46882-311D 4-7
Tx test mode
When operating in the Tx TEST mode the Service Monitor has to provide a source of modulation
for the transmitter being tested and also analyse the RF output signal from the transmitter.
Modulation sources
The modulating signal is provided by one or both of the audio generators or the data generator and
is taken from the AF output connector on the front panel.
PROGRAMM-
ABLE
ARRAY
PROGRAMM-
ABLE
ARRAY
LOOK-UP
TABLES
EPROM
LOOK-UP
TABLES
EPROM
A.F. OUTPUT
DRIVER
MODULATION
DRIVER
LOOK AND LISTEN
SWEEP DRIVER
DATA
GENERATOR
(AF GEN. 2
ONLY)
AF GEN 2
WAVEFORM
SHAPE
DATA
TO A.F.
O/P ON
FRONT
PANEL
TO R.F.
GEN.
MOD.
CONTROL
TO 90 MHz
VOLTAGE
CON-
TROLLED
OSC.
AF GEN 1
WAVEFORM
SHAPE
DATA
AF GEN 2
OUTPUT
LEVEL
DATA
AF GEN 2
FREQ.
DATA
AF GEN 1
OUTPUT
LEVEL
DATA
AF GEN 1
FREQ.
DATA
D
A
D
A
D
A
D
A
A
A
A
B
B
B
C
C1412
Fig. 4-3 AF generator detailed block diagram
Audio generators
Included in the monitor are two audio generators, shown as ‘AF generators’ on the simplified block
diagram. They are used as modulation sources for the Tx, Rx and Dx TEST modes and as audio
test signal generators in the AF TEST mode. Fig. 4-3 is a detailed block diagram of the AF
generators. They have a frequency range of 20 Hz to 20 kHz. The output waveform of either
generator can be switched between sine wave or square wave. Both generators are of similar
design, with minor variations. The generator designated ‘GEN 2’ is also used for other functions
which do not conflict with its functions as an audio generator. These uses will be mentioned where
relevant.
Each of the circuits function in the following manner:-
Instruction as to the frequency of the required signal is latched into a programmable array device,
which generates a repetitive digital output sequence recurring at the required frequency. The
digital output from the programmable array is transferred as a stream of 13 bit parallel data into an
EPROM. This holds look-up tables containing shape details of sine wave and square wave signals.