Common Analysis and Display Functions
R&S
®
FSW
488
User Manual 1173.9411.02 ─ 19
ment result, keeps the delta frequency value. Therefore the phase noise measurement
leads to reliable results in a certain offset although the source is drifting.
Using a peak as a fixed reference marker
Some results are analyzed in relation to a peak value, for example a carrier frequency
level. In this case, the maximum level can be determined by an initial peak search and
then be used as a reference point for further measurement results.
7.4.1.5
Performing a Highly Accurate Frequency Measurement (Signal Count)
A normal marker determines the position of the point on the trace and indicates the sig-
nal frequency at this position. The trace, however, contains only a limited number of
points. Depending on the selected span, each trace point may contain many measure-
ment values. Thus, the frequency resolution of each trace point is limited (see also
chapter 6.5.1.8, "How Much Data is Measured: Sweep Points and Sweep Count"
on page 407). Frequency resolution is further restricted by the RBW and sweep time
settings.
In order to determine the frequency of a signal point accurately without changing the
sweep settings, the R&S
FSW is equipped with a signal counter. The signal counter
sets the RF to the current marker position, then counts the zero crossings of the IF
(thus the term signal
counter
) and derives the precise frequency value.
Signal counting can be performed explicitely at the current marker position ("Signal
Count" marker function), or implicitely by the R&S
FSW for certain functions.
Signal counting is only possible while the instrument is not sweeping. Thus, to perform
a signal count for a marker, the sweep is stopped at the marker position. The fre-
quency is determined with the desired resolution and then the sweep is allowed to con-
tinue.
7.4.1.6
Defining a Fixed Reference Marker
Instead of using a reference marker that may vary its position depending on the mea-
surement results, a fixed reference marker can be defined for trace analysis. Once
positioned, the reference marker does not move during subsequent sweeps unless you
explicitely move it manually.
7.4.1.7
Measuring Noise Density
Using the noise measurement marker function, the noise power density is measured at
the position of the marker. In the time domain mode, all points of the trace are used to
determine the noise power density. When measurements are performed in the fre-
quency domain, two points to the right and left of the marker are used for the measure-
ment to obtain a stable result.
Result display
Noise density is the noise referred to a bandwidth of 1 Hz. With logarithmic amplitude
units (dBm, dBmV, dBmµV, dBµA), the noise power density is output in dBm/Hz, i.e. as
Marker Usage
