Tektronix TDS5054, User Manual

Page: 222 / 361

Creating and Using Math Waveforms
TDS5000 Series User Manual
3- 155
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. Therefore, if
the span is set to full, the center frequency control will not have any adjustment
range and will remain at one half of the sample rate. It is necessary to decrease
the span before the center will have an adjustment range. If you are unable to
increase the center to the desired value, 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 oscilloscope front panel.
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 RBW. Gate width has units of
seconds. The RBW 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
The Window Bin Width is the resolution bandwidth in units of bins, and depends
on the window function in use. The Gate Width is in units of seconds.
Figure 3--44 demonstrates the effects of adjusting the center frequency and span.
Center frequency is a horizontal position control for the spectrum. Span is a
horizontal scale control. Resolution bandwidth adjusts the bandwidth of the
analyzer filters without affecting the span and center frequency.