Operating instructions

LOCAL OPERATION
3-40 46882-311D
Modulation frequency and level
The frequency range and level must not exceed the following limits:-
Modulating freq. range 20 Hz to 20 kHz.
AM depth range 0 to 99% total sum of
active modulation sources.
FM deviation range 0 to 75 kHz total sum of
active modulation sources.
To enable or set up the modulation generators press the [Mod Gen] key. The screen and menu
shown in fold out diagram (4-2) will be displayed.
Set up the modulation generator(s) for the required frequency and output level by using the soft
keys and data input keys:-
[Gen 1/Gen 2] to select MOD1, then, [FREQ][n]....[n][kHz/Hz]
[LEVEL][n]...[n][kHz/Hz]
then [Gen 1/Gen 2] to select MOD2 if required,....[.../Hz]
Frequency and level increment
The FREQ [
] and [ ] and the LEVEL [ ] and [ ] keys can be assigned to the modulation
generator frequency and level. See Incremental adjustments which starts on page 3-62.
Modulation generator state
Either or both generators can be switched off to suit the test requirement. To disable a generator,
first select it using the [Gen 1/Gen 2] key. Repeated presses of the orange [ON/OFF] function
key will disable or enable the selected generator.
Note that the modulation generators are also used as AF generators to provide a
modulation source in the Tx TEST mode.
If both AF generators are set to
ON in the Tx TEST mode, switching to Rx
TEST mode will show both modulation generators to be
OFF.
Either or both generators can be set up and turned on within the Rx TEST
mode.
The frequency, level and shape settings of their last use in the Rx TEST mode will be retained
within the Rx TEST mode setup. These settings will be effective when the generators are
switched to ON in the Rx TEST mode. Their use as audio generators in the Tx TEST mode will
then be disabled.
Modulation generator shape
The shape of the output waveform from each modulation generator can be set to either sine or
square wave. To change the output waveform from a generator, first select it using the
[Gen 1/Gen 2] key. Repeated presses of the [Shape] key will toggle between sine or square wave.
Modulation generator level locking
Pressing the [Lock] key locks the output level of the two modulation generators to the same level.
The unselected generator locks to the level of the selected generator.
Pre-emphasis filter
The pre-emphasis filter can be switched in or out of circuit after pressing the [Mod Gen] key.
Pressing the [Pre-emph] key will toggle the pre-emphasis filter into and out of circuit. The time
constant of the filter is 750 µs, giving an increase with frequency of 6 dB/octave.
The legend
Pre-emph ON is displayed when the filtering is in circuit. No indication is given
when the filtering is out of circuit.