Radio Test Instruments
Subject to Export Control, see Cover Page for details.
7-9
[Coupling] Soft Key
Accesses a Soft Key sub-menu that allows user to define Resolution and Video Bandwidths as
well as Sweep Time.
Fig. 7-10 Channel Analyzer Coupling Soft Key Menu
RBW, VBW and Sweep Time are all interdependent and govern the usefulness of a Channel
Analyzer trace. These Soft Keys are controlled by inter-related action so that changing the value
of one changes one or both of the others to optimize the display and prevent an invalid setting.
RBW, VBW and Sweep Time can be set to AUTO or MANUAL operation.
For many applications, setting all three parameters to AUTO provides a useful representation
of the signal to be examined. However, parameters can be set to specific requirements,
allowing the Test Set to select the optimum setting for the other two parameters according to
internal setup tables.
[Res BW] (Resolution Bandwidth) Soft Key
Sets the bandwidth of the IF filter. Resolution is the ability of the Channel Analyzer to
discriminate between signals closely separated in frequency. For example, if two tones are
analyzed, the Channel Analyzer is only able to discriminate between them if the resolution
bandwidth selected is narrower than the tone separation. Filter selection becomes more critical
if the tones are at different levels. Narrow resolution bandwidth also results in lower noise on
the trace.
Power Measurement
When using the Channel Analyzer to perform power measurements, the Resolution Bandwidth
must be set to a value equal or greater than the bandwidth of the signal being measured.
[Vid BW] (Video Bandwidth) Soft Key
To view signals close to the noise level, a low pass filter (called the video filter) is introduced
after the detector. The Video Bandwidth is the high frequency cutoff point of the filter. The
video filter reduces high frequency noise on the detected signal and enables low level signals to
be identified that would otherwise be buried in the noise.
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