Configuring the Internal Baseband Source
R&S
®
SMW200A
247User Manual 1175.6632.02 ─ 16
The signal generation starts simultaneous in all basebands but you can still delay the
basebands compared to each other.
In test setups that require the signal of two or more baseband sources but that do not
use the advantages of the coupled trigger setting, trigger the baseband sources from a
common trigger source. Use for example an external trigger source or to distribute the
internal trigger signal of one of the basebands to the other.
For a step-by-step description, see Chapter 4.5.3.1, "Trigger the Baseband Sources
with a Common Signal", on page 262.
4.5.1.4 Supported Modulation Types
The R&S SMW supports a range of predefined digital and analog modulation types.
This section focuses on the possibility to digitally modulate the baseband signal. The
analog modulation methods provided for shifting the frequency bandwidth of the RF
signal are described in Chapter 7.7, "Analog Modulations", on page 493.
In the communication techniques, the commonly used digital modulation schemes are
based on keying. From the several existing keying techniques, this instrument supports
ASK (amplitude shift keying), FSK (frequency shift keying), PSK (phase shift keying),
and QAM (quadrature amplitude modulation). The digital modulation procedure is
described by mapping. That is, by the assignment of I and Q values (PSK and QAM) or
frequency shifts (FSK) to every modulation symbol. The resulting modulated signal is
graphically represented by a constellation diagram, in that each possible symbol is rep-
resented by a discrete point on a complex plane. The number of used bits per symbol
is a modulation parameter. The exact position of the symbols on the constellation dia-
gram is determined by the used coding and can be influenced by additionally applied
rotation.
Most of the provided modulation schemes are implemented according to a communica-
tion standard. The QAM procedures 16QAM, 32QAM, 64QAM for instance have been
produced in accordance with ETSI standard ETS 300429 for digital video broadcasting
(DVB). The QAM procedures 256QAM and 1024QAM are not specified in this stan-
dard, but have been produced according to the same basic principles.
In the case of all FSK procedures, you can set the symbol rate f
SYMB
up to a maximum
value (see data sheet). The frequency deviation (FSK deviation) of the MSK modula-
tion is permanently set to ¼ of the symbol rate.
In addition to the common modulation schemes, a variable FSK modulation with defin-
able deviation per symbol is available and for even greater flexibility, a user-defined
modulation mapping can be applied (see "User mapping" on page 247).
Predefined modulation types
Refer to Chapter 4.6.5.1, "Predefined Modulation Types", on page 292 for an overview
of the available modulation types.
User mapping
A user-defined modulation mapping file can also be selected as modulation mapping
source. The user modulation mapping file must have extension *.vam and can be cre-
Common Functions and Settings in the Baseband Domain
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