Demodulation Bandwidth; Sample Rate, Measurement Time And Trigger Offset - R&S FSV-K7 Operating Manual

®
R&S FSV-K7/K7S
The AM DC, FM DC and PM DC raw data of the demodulators is fed into the Trace
Arithmetic block that combines consecutive data sets. Possible trace modes are:
Clear Write, Max Hold, Min Hold and Average (for details refer to
Mode
be read via remote control.
The collected measured values are evaluated by the selected detector (for details refer
to Chapter 2.1.8, "Detector
screen and can be read out via remote control.
In addition, important parameters are calculated:
●
A counter determines the modulation frequency for AM, FM, and PM.
●
average power = carrier power (RF power)
●
average frequency = carrier frequency offset (FM)
●
The modulation depth or the frequency or phase deviation is displayed.
●
AC coupling is possible with FM and PM display. The deviations are determined
from the trace data. +Peak, –Peak, ½ Peak-Peak and RMS are displayed.

2.1.2 Demodulation Bandwidth

The demodulation bandwidth is not the 3 dB bandwidth but the useful bandwidth which
is distortion-free with regard to phase and amplitude.
Therefore the following formulas apply:
●
AM: demodulation bandwidth ≥ 2 x modulation frequency
●
FM: demodulation bandwidth ≥ 2 x (frequency deviation + modulation frequency)
●
PM: demodulation bandwidth ≥ 2 x modulation frequency x (1 + phase deviation)
If the center frequency of the analyzer is not set exactly to the signal frequency, the
demodulation bandwidth must be selected larger by the carrier offset, in addition to the
requirement described above. This also applies if FM or PM AC coupling has been
selected.
In general, the demodulation bandwidth should be as narrow as possible to improve
the S/N ratio. The residual FM caused by noise floor and phase noise increases dra-
matically with the bandwidth, especially with FM.

2.1.3 Sample Rate, Measurement Time and Trigger Offset

Depending on the sample rate, the maximum demodulation bandwidths listed in the
table can be obtained during the measurement. The permissible value range of the
measurement time and trigger offset depends on the selected demodulation bandwidth
and demodulation filter. If the AF filter or the AF trigger are not active, the measure-
ment time increases by 20 %.
Operating Manual 1176.7561.02 ─ 06
Overview", on page 17. The output data of the Trace Arithmetic block can
Overview",
Analog Demodulation Option R&S FSV–K7
Instrument Functions Analog Demodulation
on page 19. The result is displayed on the
Chapter 2.1.7, "Trace
13