R&S FSH Setting the Span
1309.6275.12 4.5 E-2
Channel numbers are assigned to frequencies as follows:
- The first channel is assigned a channel number and a frequency.
- All subsequent channels have ascending numbers.
- The frequency spacing between channels is fixed. It can also be negative, i.e. the center frequency
of the R&S FSH decreases with ascending channel number.
- In transmission systems containing gaps in the frequency range (as in the case of television, for
example), a channel table can comprise multiple ranges.
Setting the Span
The span is the frequency range centered on the center frequency which a spectrum analyzer displays
on the screen. What span should be selected for a particular measurement depends on the signal to be
investigated. A rule of thumb is that it should be at least twice the bandwidth occupied by the signal.
For frequency domain measurement the R&S FSH4 has a minimum span of 100 Hz and a maximum
span of 3.6 GHz. Using the span 0 Hz measurement is performed in time domain. The maximum span
is 8 GHz with the R&S FSH8.
Operating sequence:
Press the SPAN key.
When the SPAN key is pressed, the R&S FSH
automatically activates the MANUAL SPAN softkey
and indicates the current value so that a new span can
be entered immediately. If another function in the
SPAN menu has been used beforehand, press the
MANUAL SPAN softkey to enter the span.
Enter a new span with the number keys and
terminate the entry with the appropriate unit (GHz,
MHz, kHz or Hz), or
Change the span with the rotary knob or the cursor
keys. The span is set immediately after the change
is made.
The value entry box can be cleared from the
screen with the CANCEL key.
Use the FULL SPAN softkey to select the maximum span with a single keystroke.
Press the FULL SPAN key.
The R&S FSH displays the spectrum over the full span which extends to 3.6 GHz or to 8 GHz.
(CENTER = 1.8 GHz, SPAN = 3.6 GHz, CENTER = 4 GHz, SPAN = 8 GHz).
The R&S FSH has a LAST SPAN softkey so that you can toggle between span settings with just one
keystroke.
Press the LAST SPAN key.
The span that was set immediately before the current span is restored.
The ZERO SPAN softkey sets the span to 0 Hz. The R&S FSH measures the signal level only at the
center frequency that has been set. As a spectrum cannot be displayed when measurements are made
at a single frequency, the display mode switches to the time domain. The x axis of the measurement
diagram becomes the time axis and level is plotted against time. The display always starts at 0 s and
stops after the sweep time that has been set (set with the SWEEP key, see also "Setting the Sweep").
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