INDIVIDUAL SOURCE OPERATION
3-20
(7) Press
[Phase Diff]
and adjust the phase using the control knob. Turn clockwise to advance
the phase and anticlockwise to retard the phase. Note that if you have set the source phase
and subsequently adjusted the source frequency or changed the waveform, the menu
Phase
Difference:
value will be blanked. This is because the value will then be indeterminate due to
the adjustment or changed waveform.
(8) To establish a reference, the displayed phase shift can be reset to 0.0
°
by pressing
[Reset
Phase].
(9) Press
[EXIT]
to return to the Signal Generator menu.
External source coupling
Having selected an external modulation mode, you can select the type of external coupling as
follows:
(1) Press [SIG GEN] and show the Signal Generator menu for a single modulation mode.
(2) Press
[Select Coupling]
to display the
External Source Coupling Menu
. This shows the
currently selected modulation and external coupling (see Fig. 3-15 below).
B3906
Fig. 3-15 External source coupling menu
(the [DCFM Nulling] key only appears during FM
external modulation mode with DC coupling)
(3) Select
between
[Ext AC Coupling], [Ext ALC Coupling]
and
[Ext DC Coupling].
The screen
changes to show your new coupling selection.
(4) Apply a signal to the MOD I/O socket.
(5) When Automatic Leveling Control is selected by pressing
[Ext ALC Coupling],
and the error
message
Err 511: ALC too high
or
Err:512: ALC too low
is displayed, the level must be
adjusted. Adjust the signal level until it is within the 0.75 to 1.25 V RMS ALC range of the
source.
(6) Press
[EXIT]
to return to the Signal Generator menu.
DCFM nulling
For a DC-coupled external signal, small frequency offsets can be reduced by using the DCFM
nulling facility. Operation is as follows:
(1) With
FM External
mode previously selected from the
Modulation Mode Selection Menu
press the
[Ext DC Coupling]
key shown in Fig. 3-15 above.
(2) Connect your ground reference to the MOD I/O socket.
(3) Press
the
[DCFM Nulling]
key which is now displayed.
* DCFM Nulling *
appears during
the nulling process and when it disappears the process is completed.
