Rohde & Schwarz FPC Series, User Manual

Page: 129 / 419

The Spectrum Application
R&S
®
FPC
126 User Manual 1178.4130.02 ─ 07
● Noise Measurement ..............................................................................................126
● Frequency Counter ............................................................................................... 126
● Signal Bandwidth Measurement ........................................................................... 127
● Marker Demodulation ............................................................................................128
14.10.1 Noise Measurement
Access : "Mkr" > "Marker Mode" > "Noise"
The marker noise measurement calculates the noise power density at the marker posi-
tion in dBm/Hz. The R&S
FPC includes several variables in the calculation of the noise
power density, including the trace pixel values, the resolution bandwidth, the detector
and the level display mode (absolute or relative). To stabilize the noise power display,
the R&S
FPC uses the pixel the marker is on and four pixels to the right and four pixels
to the left of the marker pixel.
Noise power density can provide useful information when you are measuring noise or
digitally modulated signals. However, you will get valid results only if the spectrum in
the vicinity of the marker has a flat frequency response. When measuring the noise
power density on discrete signals, results are not valid.
Note that the noise measurement only works for marker 1 (M1) or delta marker 2 (D2).
Measuring the noise density
1. Press the "Mkr" key to open the marker menu.
2. Select the "Marker Mode" menu item to open the marker function menu.
3. Select the "Noise" menu item.
The R&S FPC shows the noise density at the marker frequency in the marker list in
dBm/Hz. If you are using a delta marker for the measurement, the results have the
unit dBc/Hz with marker
1 being the reference. This is useful for phase noise mea-
surements, for example.
4. Select the "Noise" menu item again to turn off the noise measurement.
14.10.2 Frequency Counter
Access : "Mkr" > "Marker Mode" > "Frequency Count"
The R&S FPC provides a frequency counter. The frequency counter accurately meas-
ures the frequency at the position of marker 1 (M1).
When calculating the horizontal position of the marker, the R&S FPC includes the cur-
rent span, center frequency and the frequency of the pixel the marker is on. As the
trace only has a limited number of pixels, the marker position is usually just an approxi-
mation, especially if the span is very large.
With the frequency counter, however, you can get a more accurate result of the fre-
quency that the marker is positioned on. If the frequency counter is active, the
Marker Functions