R&S FSW Series, Руководство пользователя

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Common Measurement Settings
R&S
®
FSW
442 User Manual 1173.9411.02 ─ 43
For example, to analyze signal harmonics, you can define the step size to be equal to
the center frequency. In this case, each stroke of the arrow key selects the center fre-
quency of another harmonic. Similarly, you can define the step size to be equal to the
current marker frequency.
8.3.1.3 Coping with Large Frequency Ranges - Logarithmic Scaling
In a linear display, the frequencies are distributed linearly across the x-axis. That
means the entire frequency range is divided by the number of sweep points, and the
distance between sweep points is equal. Linear scaling is useful to determine precise
frequencies within a small range.
1 MHz 10 MHz
Figure 8-22: Linear x-axis scaling: the distance between the sweep points is equal, e.g. 200 kHz
However, if high and low frequencies appear in the same display, it is difficult to deter-
mine individual frequencies precisely or to distinguish frequencies that are close
together.
In a logarithmic display, lower frequencies are distributed among a much larger area of
the display, while high frequencies are condensed to a smaller area. Now it is much
easier to distinguish several lower frequencies, as they are spread over a wider area.
Logarithmic scaling is useful for overview measurements when a large frequency
range must be displayed in one diagram.
However, with logarithmic scaling, the frequency resolution between two sweep points
deteriorates with higher frequencies.
1 Hz 1 GHz
1 MHz
Figure 8-23: Logarithmic x-axis scaling: the distance between sweep points is variable
In the spectrum from 10 Hz to 100 Hz, the distance is a few Hz. Between 100 MHz and
1 GHz, the distance is several MHz.
Thus, for logarithmic x-axis scaling, the number of sweep points must be sufficiently
high in order to distinguish high frequencies precisely. The resolution bandwidth should
cover at least one sweep point (that means: the distance between two sweep points
should not exceed the RBW). If this condition is not met, signals or interferers could be
missed, especially narrowband interferers.
Frequency and Span Configuration