Creating and Using Math Waveforms
3- 186
CSA7000B Series & TDS7000B Series Instruments User Manual
H Center. This is the frequency at the center of the spectral waveform. Center is
equal to the start frequency plus one half of the span. The adjustment range
depends on the sample rate and the current span setting. Remember that the
span must always be in the interval of zero to one half of the sample rate.
Where one end of the span goes to DC or Nyquist, depending on which
direction the center frequency is adjusted, the span decreases to allow the
center frequency to go further in the direction it is being adjusted. If you are
unable to increase the center to the desired value then increase the sample
rate using either the sample rate or resolution controls. You may also change
sample rate by using the HORIZONTAL SCALE knob on the instrument
front panel.
H Resolution Bandwidth, RBW. This is the 3 dB down bandwidth of the
spectral analyzer frequency response to a sine wave input. The resolution
bandwidth is affected by two parameters.
H Different window functions produce different filter response shapes in
the spectrum and result in different resolution bandwidths.
H The gate width, of the input data, affects the resolution bandwidth
(RBW). Gate width has units of seconds. The resolution bandwidth
directly controls the gate width, but the numerical value is entered in
units of Hz. Therefore, the time domain gate markers move as you adjust
the RBW control.
RBW =
Window Bin Width
Gate Width
Where the Window Bin Width is the resolution bandwidth in units of bins. It
depends on what window function is used. The gate width is in units of
seconds.
Figure 3--49 demonstrate the effects of adjusting center frequency and span.
Center frequency is a horizontal position control for the spectrum. Span is a
horizontal scale control. Resolution bandwidth usually adjusts the bandwidth of
the analyzer filters without affecting the span and center frequency.
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