Quick Start
R&S
®
ESRP
110
User Manual 1175.7445.02 ─ 08
b) Switch the "Trg/Gate Polarity" softkey to "Neg."
The R&S
ESRP initiates triggering in response to the falling edge of the burst.
This shifts the burst to the left-hand half of the measurement diagram. The
power is measured in the deactivation phase. The start of the burst is shifted to
the center of the screen and the power during the deactivation phase is mea-
sured.
Figure 3-19: Measurement of the signal-to-noise ratio of a GSM burst signal in zero span.
3.5.4.3
Measuring FM-Modulated Signals
Since signal analyzers can display only the magnitude of the measurement signal by
using the envelope detector, the modulation of FM-modulated signals cannot be mea-
sured directly as in the case of AM-modulated signals. The voltage at the output of the
envelope detector remains constant for FM-modulated signals as long as the fre-
quency deviation of the signal is located within the flat part of the passband character-
istic of the employed resolution filter. Amplitude variation occurs only if the instantane-
ous frequency extends into a falling edge of the filter curve. This behavior can be used
to demodulate FM-modulated signals. The center frequency of the analyzer is set in
such a manner that the nominal frequency of the measurement signal is located on a
filter edge (below or above the center frequency). The resolution bandwidth and the
frequency offset must be selected in such a manner that the instantaneous frequency
is located in the linear part of the filter edge. As a result, the frequency variation of the
FM-modulated signal is transformed into an amplitude variation that can be displayed
on screen in zero span.
Basic Measurement Examples
