Common Measurement Settings
R&S
®
FSW
386
User Manual 1173.9411.02 ─ 19
found within the searched bandwidth. If no maximum signal above a defined threshold
value is found in the searched bandwidth, the center frequency remains unchanged.
The search bandwidth and the threshold value are shown in the diagram by red lines
which are labeled as "TRK".
6.3.1.4
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.
Fig. 6-20: 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 amoung 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 span must be
displayed in one diagram.
However, with logarithmic scaling, the frequency resolution between two sweep points
deteriorates with higher frequencies.
Fig. 6-21: 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.
Frequency and Span Configuration
