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LOCAL OPERATION

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(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 Sig Gen 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 Sig Gen 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). The [DCFM

Nulling] key appears only during FM external modulation mode with DC coupling.

B3417

Fig. 3-15 External source coupling menu

(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 Levelling 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 Sig Gen 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.

IFR 2026 User Manual

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