Multi-instrument setups
R&S
®
SMM100A
452
User Manual 1179.1341.02 ─ 05
factor. For example, the crest factor of the external signal is important for the calcula-
tion of the RF output power.
Figure 9-2: Relation between the level settings
Test setups often involve an up-converter connected to the I/Q connectors of the gen-
erator or feeding of external signal to the digital input of the R&S
SMM100A. As a rule,
whenever an I/Q signal is transferred between two instruments,
the crest factor and the
peak levels of the two involved instruments have to be coordinated
.
To ensure proper signal settings and correct results, check if the peak level values and
crest factor values are equal. Equal values hold for the I/Q outputs of the
R&S
SMM100A and the I/Q inputs of the up-converter are equal.
In the R&S
SMM100A, level values are represented as relative to a full scale (see
Where to find the necessary values
●
Dialog "BB Input"
Why the instrument monitors the signal internally and how to avoid overflow
The R&S
SMM100A constantly monitors the input and output digital signal and indi-
cates an overflow status.
●
Overflow of the
input signal
(crest factor and peak level) is indicated if the entered
"Peak Level" (in dB full scale) value does not correspond to the real value
Tip:
The overflow status is indicated as long as the signal level is not reduced and
the peak level value corrected. Trigger "Auto Level Set" to collect the required val-
ues and adjusts the settings automatically.
●
Overflow of the
output signal
is indicated if the digital signal is clipped, i.e. if the
level of the output signal, or the noise level (AWGN) are too high.
Specific characteristics of the digital I/Q interface
What is a "digital channel" and how are the channels distributed to the base-
bands
The external digital signals supplied at the Dig I/Q interfaces of the instrument can con-
tain more than one, possibly even multiplexed, digital channels. The R&S
SMM100A
processes each of these digital channels as a separate signal.
The external digital signals supplied at the HS Dig I/Q interfaces of the instrument can
contain more than one, possibly even multiplexed, digital channels. The
R&S
SMM100A processes each of these digital channels as a separate signal.
Control and operation of external instruments
