Rohde & Schwarz FSQ series, Quick Start Manual

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Quick Start Guide 1313.9652.62 - 02 5.15
R&S FSQ Basic Measurement Examples
Measuring Signal Spectra with Multiple Signals
5.4 Measuring Signal Spectra with Multiple Signals
5.4.1 Separating Signals by Selecting the Resolution Bandwidth
A basic feature of an analyzer is being able to separate the spectral components of a mixture
of signals. The resolution at which the individual components can be separated is determined
by the resolution bandwidth. Selecting a resolution bandwidth that is too large may make it
impossible to distinguish between spectral components, i.e they will appear as a single
component.
An RF sinusoidal signal will be shown on the screen by means of the passband characteristic
of the resolution filter (RBW) that has been set. Its specified bandwidth is the 3 dB bandwidth
of the filter.
Two signals with the same amplitude can be resolved if the resolution bandwidth is smaller
than or equal to the frequency spacing of the signals. If the resolution bandwidth is equal to
the frequency spacing, the spectrum display screen will show a level drop of 3 dB precisely in
the center of the two signals. Decreasing the resolution bandwidth makes the level drop larger,
which thus makes the individual signals clearer.
The trade-off for higher spectral resolution at a narrower bandwidth is longer sweep times at
the same span. Reducing the resolution bandwidth by a factor of 3 increases the sweep time
by a factor of 9.
5.4.1.1 Separating Two Signals with a Level of –30 dBm each at a Frequency Spacing
of 30 kHz
Test setup:
Setting the signal generators:
Level Frequency
Signal generator 1 -30 dBm 100.00 MHz
Signal generator 2 -30 dBm 100.03 MHz
Signal
generator 1
Signal
generator 2
Coupler
R&S FSQ