GENERAL
4-45
DCFM nulling
For a DC-coupled external FM signal, small frequency offsets can be reduced by using the DCFM
nulling facility. Operation is as follows:
(1) First of all select external FM from Util 20: Modulation Mode (Normal). Then select DC
coupling from Util 30: Modulation Source.
(2) Select the Util 23: DCFM Nulling utility shown in Fig. 4-39 below.
B2061UT023
Fig. 4-39 DCFM nulling display
(3) Follow the on-screen directions by connecting your ground reference to the EXT MOD
INPUT socket.
(4) With DCFM Null highlighted press [SELECT]. * DCFM Nulling * appears during the
nulling process and when it disappears the process is completed.
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