Power Measurements – MEAS Key R&S FSL
1300.2519.12 4.78 E-11
To measure the carrier–to–noise ratio
1. Press the C/N, C/No softkey to configure the carrier–to–noise ratio measurement.
T
he corresponding submenu is displayed.
2. To activate the measurements without reference to the bandwidth, press the C/N softkey.
3. To activate the measurements with reference to the bandwidth, press the C/No softkey.
4. To change the channel bandwidth for the transmission channel, press the Channel Bandwidth
softkey.
5. To optimize the settings for the selected channel configuration, press the Adjust Settings softkey
(for details see also "Settings of CP / ACP test parameters" on page 4.80).
Power measurement in zero span
With the aid of the power measurement function, the R&S FSL determines the power of the signal in
zero span by summing up the power at the individual measurement points and dividing the result by the
number of measurement points. In this way it is possible to measure for example the power of TDMA
signals during transmission or during the muting phase. Both the mean power and the RMS power can
be measured by means of the individual power values.
The result is displayed in the marker field. The measured values are updated after each sweep or
averaged over a user–defined number of sweeps in order to determine e.g. the mean power over
several bursts. For determination of the peak value the maximum value from several sweeps is
displayed.
If both the on and off phase of a burst signal are displayed, the measurement range can be limited to
the transmission or to the muting phase with the aid of vertical lines. The ratio between signal and noise
power of a TDMA signal for instance can be measured by using a measurement as a reference value
and after that varying the measurement range.
Upon switching on power measurement the sample detector is activated.
Measurement of occupied bandwidth
An important characteristic of a modulated signal is its occupied bandwidth. In a radio communications
system for instance the occupied bandwidth must be limited to enable distortion–free transmission in
adjacent channels. The occupied bandwidth is defined as the bandwidth containing a defined
percentage of the total transmitted power. A percentage between 10% and 99.9% can be set.
The measurement principle is the following: The bandwidth containing 99% of the signal power is to be
determined, for example. The routine first calculates the total power of all displayed points of the trace.
In the next step, the points from the right edge of the trace are summed up until 0.5% of the total power
is reached. Auxiliary marker 1 is positioned at the corresponding frequency. Then the points from the
left edge of the trace are summed up until 0.5% of the power is reached. Auxiliary marker 2 is
positioned at this point. 99% of the power is now between the two markers. The distance between the
two frequency markers is the occupied bandwidth which is displayed in the marker field.
To ensure correct power measurement, especially for noise signals, and to obtain the correct occupied
bandwidth, the following prerequisites and settings are necessary:
• Only the signal to be measured is displayed on the screen. An additional signal would falsify the
measurement.
• RBW << occupied bandwidth
(approx. 1/20 of occupied bandwidth, for voice communication type 300 Hz or 1 kHz)
• VBW
3 x RBW
• RMS detector
• Span
2 to 3 x occupied bandwidth
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