Rohde & Schwarz R&S FSP Series, Operating Manual

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Operating Manual 1164.4556.12 - 06 2.39
R&S FSP Getting Started
Measurements on Modulated Signals
2.5.3.4 Measurement Example 4 – Measuring the Transient Spectrum in Burst Mode
with the Fast ACP function
In addition to the modulation spectrum or adjacent channel power from the modula-
tion of the RF carrier, the spectrum or adjacent channel power generated by burst
edges is also to be measured in TDMA systems. The spectrum is a pulse spectrum
and must be measured with the peak detector. With the usual IBW method, only the
power of the continuously modulated signal can be measured properly. Even if the
modulation spectrum is transmitted in the TDMA mode, the measurement of the
modulation spectrum will work because the burst edges are blanked out for the
measurement by means of the Gated Sweep function. The R&S FSP performs mea-
surements only if the modulation spectrum is continuous when the burst is on.
However, the IBW method fails for the spectrum created by the burst edges. As the
measurement is carried out with resolution bandwidths that are very small compared
to the signal bandwidth, a spurious amplitude distribution is obtained in the defined
measurement channel because of the resolution bandwidth. The small resolution
bandwidth cannot settle to the peak amplitudes of the test signal. This problem is
avoided in the R&S FSP by performing time domain measurements with the root
raised cosine filter specified in the IS136 standard.
If the peak detector is used instead of the default RMS detector (which is selected
when the standard is selected), the true adjacent channel power generated by the
burst edges can also be measured.
Test setup:
The test setup for this example and the settings for R&S SMIQ are identical to those
in the previous example.
Measurement with the R&S FSP:
1. Set the R&S FSP to its default state.
➢
Press the PRESET key.
The R&S FSP is in its default state.
2. Synchronize the R&S FSP to an external reference frequency.
➢
Press the SETUP key.
➢
Set the REFERENCE softkey to EXT .
3. Set the center frequency to 850 MHz
➢
Press the FREQ key and enter 850 MHz .
4. Configure the adjacent channel power measurement for IS136 signals in
Fast ACP mode.
➢
Press the MEAS key.
➢
Press the CHAN PWR ACP ! softkey.
The selected sweep time is the net sweep time, i.e. the time during which the
R&S FSP is actually measuring. The complete frame of an IS136 signal takes 40
ms. In the above example, measurement only takes place for 2x5 ms within a
frame. The R&S FSP is therefore only measuring for 25% of the frame duration.
The total measuring time is therefore four times that for the CW mode.