HP 8920A - Page 282

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S:\HP892XX\USRGUIDE\manual\decoscrn.fb
Chapter 8, Signaling Decoder Screen
Continuous Digital Controlled Squelch System Decoder
Input Level
This field specifies the signal level that you input (after de-emphasis if used). The
higher the level of signal expected by the analyzer, the higher the trigger level is
set.
Operating Considerations
The unit-of-measure is determined by the AF Anl In setting.
The input level should be set high enough to prevent false triggering, but low
enough to detect all valid zero-crossings of the incoming signal.
When using de-emphasis, the
Input Level setting may need to be reduced
significantly to properly decode the incoming signal. De-emphasis is enabled/
disabled using the
De-Emphasis field on the AF ANALYZER screen.
See Also
Trig Level
field description, on page 283
Polarity
This field is used to match the polarity of the encoded signal being analyzed.
Normal Operation. When this field is set to
Norm, a logical high (1) is displayed
when a positive peak in the received signal is detected. A negative peak displays a
logical low (0).
Inverted Operation. When this field is set to
Invert, a logical low (0) is
displayed when a positive peak in the received signal is detected. A negative peak
displays a logical high (1).
Operating Considerations
Inverting amplifiers used in transmitters, receivers, and repeaters can cause an
inversion of the modulating digital data. If the decoded signal does not display the
expected results, change this field’s setting to see if the signal may be getting
inverted before being decoded.