DETAILED OPERATION
4-25
Source selection − external
AC or DC coupling or automatic leveling control (ALC) can be used in conjunction with an
external source. Having previously selected external modulation from the Util 20 Modulation
Mode menu continue as follows:
(1) Press [MOD SOURCE] for modulation source selection.
(2) Repeatedly press [MOD SOURCE] to cycle through the selections Ext DC, Ext AC and Ext
ALC.
(3) Apply a signal to the EXT MOD INPUT socket. Note that on switch-on this socket is
disabled.
(4) If EXT ALC has been selected and the error message Err 511: ALC too high or Err 512:
ALC too low is displayed the signal input is outside the 0.75 to 1.25 V RMS ALC range of
the instrument.
(5) If EXT DC has been selected, note that a DCFM nulling facility is available (refer to
‘DCFM nulling’ in the ‘General’ section below).
External source selection may also be made by means of the Util 30: Modulation Source menu
shown in Fig. 4-22.
Fig. 4-22 Modulation source menu
−
shown with an external source selected
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