HP 8920A - Page 488

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S:\HP892XX\USRGUIDE\manual\rfgscrn.fb
Chapter 18, RF Generator Screen
Field Descriptions
Atten Hold
Attenuator hold prevents the fixed RF output attenuators from switching in and
out, eliminating the loss of the output signal as the level is changed. This function
is helpful when making squelch measurements.
Operating Considerations
When this function is set to On, the RF output level is restricted to a range above
and below the present
Amplitude setting. Attempting to set an amplitude outside
the allowed range results in an error message and beep (if the beeper is on). RF
output level accuracy is greatly degraded outside the allowed range.
Audio Out
Audio output coupling selects ac or dc coupling to the AUDIO OUT connector.
FM Coupling
These fields provide two functions:
• The upper field specifies ac or dc coupling between the MODULATION INPUT con-
nector and the RF Generator’s FM modulator. This field also alters the FM modulator
to allow DCFM from internal and external modulation sources.
• Selecting the lower field causes the instrument to offset any dc bias that may exist when
dc coupling is selected.
Mic Pre-Emp
Microphone pre-emphasis determines whether the modulating signal from the
MIC/ACC connector goes through or bypasses the 750 ms pre-emphasis network.
Two fields are used:
• The upper field is used to specify whether you want the instrument to automatically turn
pre-emphasis on during FM operation and off for other modulations (Auto), or to leave
the pre-emphasis switching to the user’s operation (Hold).
• The lower field tells you whether pre-emphasis is on or off (when Auto operation is
selected), or allows you to manually turn pre-emphasis on or off (if Hold is selected).