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ANALOG MODULATION MODE
3-56
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.
If pulse modulation is not fitted 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.
If pulse modulation (Option 002) is fitted proceed as follows:
(1) Press the
[Pulse Mod]
key.
(2) This causes the message
PULSE ON
to be displayed.
(3) Press the
[Pulse ON/OFF]
key.
(4) This causes
PULSE OFF
to be displayed together with
Low Intermodulation Disabled
or
Low
Intermodulation Enabled
shown in the lower panel.
(5) Press the [MOD ON-OFF] key to toggle between the enabled and disabled states.
(6) If an attempt is made to
[Set Steps]
from the
Δ
menu, the message
PULSE : No Steps Allowed
will be displayed.
AM is not available in the Pulse Modulation or Low Intermodulation modes of operation.