Rohde & Schwarz R&S SMU200A, Руководство по обслуживанию

Страница: 158 / 294

R&S SMU200A Troubleshooting
1007.9845.82 3.31 E-6
Faulty Signal Generation in the Baseband
•
Error: Vector Signal Generator does not supply correct baseband signal (at I+Q output
sockets on rear panel and/or digital modulation disturbed).
Normal action Test
Baseband signal is generated on the Universal
Coder (UNICOD) board and transferred via
motherboard to the DACIF board. Placed on this
board are the D/A converters (DAC board), which
feed analog signals to the rear panel sockets and
to module IQOP3. The Graphics facility takes
data from UNICOD for constellation diagram and
from DAC board for power spectrum. Setting on Vector Signal Generator:
Baseband/Custom Digital Modulation
Set acc. to standard TETRA
State On
Graphics/Graphic Settings
Mode Constellation
A set of 8 points, equally spaced on a circle with
0.7 radius should appear.
If not, UNICOD is faulty.
Setting on Vector Signal Generator:
Graphics/Graphic Settings
Mode Power Spectrum
A clean, nearly rectangle shaped power spectrum
should appear without sidelobes.
If not, DACIF board or DAC board (mounted on
DACIF) is faulty.
•
Error: Vector Signal Generator does not supply any baseband signal (UNICOD, FADER,
and DACIF).
Normal action Error and error cause
Same setting as above, but with FADER whereby
FADER should be set to OFF (i.e. bypass in the
first FGPA on the FADER). Select a modulation
(e.g. DIGMOD, QPSK) in the baseband. The
modulation is set on the UNICOD board and the
level and RMS are checked directly at the output
of this board. The expected constellation diagram (e.g. 4
scatterplots for QPSK) does not appear in the
graphical display:
Repeat test without fader:
Signal now OK:
Fault on fader
The data of the UNICOD is transferred to the
DACIF where it is received on the DAC boards.
From here the IQ data can be displayed in the
graphical window in the operator control window.
The FADER should be set to OFF. The expected constellation diagram (e.g. 4
scatterplots for QPSK) does not appear in the
graphical display:
Connection possibly defective.
Check plug-in contacts between UNICOD and
motherboard, between motherboard and
DACIF and DACB.
Connection OK:
DAC board is probably
defective.
No analog signal:
Check graphical display
Signal OK:
Check output of DACIF