OPERATION
3-1-35
MODULATION ALC
The automatic leveling control (ALC) is used in conjunction with an external source and
can be disabled when not required. To enable the ALC, proceed as follows:
(1) At
the
Sig Gen
menu, press
[Select Source]
. The display will show the
Internal
or
External Source Selection Menu
(Fig. 3-1-27 or Fig. 3-1-29).
(2)
If necessary press
[Select External]
to obtain the
External Source Selection Menu
(Fig. 3-1-29).
(3)
Select the required external source from the options shown, e.g.
[Ext 1 ALC
Coupling]
or
[Ext 2 ALC Coupling]
. The pictogram at the end of each line will
change from a horizontal line to an arbitrary waveform symbol when the source is
selected.
(4)
Return to the
Sig Gen
menu by pressing [SIG GEN]. The legend
Ext Mod 1 (
or
2)
ALC coupled
appears at the bottom of the display.
(5)
Apply a signal to the EXT MOD 1 or EXT MOD 2 input socket and vary the
level. If the input applied to the external modulation socket is outside the ALC
range (at least 0.7 to 1.4 V RMS)
HI
LO
will be indicated and an error message
will be displayed at the top of the screen. If the level is within the required range,
the arbitrary waveform symbol will appear alongside the modulation value.
Low intermodulation mode
When carrying out intermodulation tests the output signal from two signal generators is
combined using a resistive or hybrid combiner. If the carrier frequencies are relatively close
together each generator will receive an interfering signal from the other source. The RF ALC
system will detect a beat frequency equal to the difference in carrier frequencies and attempt to
apply AM in order to cancel the signal. In so doing the RF ALC system will generate AM
sidebands which are indistinguishable from intermodulation products. By using the low
intermodulation mode the RF ALC system can be disabled to prevent the injection of AM
sidebands.
Proceed as follows:
(1) At
the
Sig Gen
menu press
[Low Intermod].
(2)
This causes either
Low Intermodulation Disabled
or
Low Intermodulation
Enabled
to be displayed in the lower panel.
(3)
Press the [MOD ON-OFF] key to toggle between the enabled and disabled states.
(4)
If an attempt is made to
[Set Steps]
from the
Δ
menu, the message
Low Intermod:
No Steps Allowed
will be displayed.
Note...
AM is not available in the Low Intermodulation mode of operation.