Instrument Function
R&S
®
SMB100A
198
Operating Manual 1407.0806.32 ─ 21
Internal Modulation Sources
An LF generator and a pulse generator are available as internal modulation sources for
a fully equipped instrument. The LF generator supplies sinusoidal or rectangular sig-
nals.
The optional pulse generator (option R&S
SMB-K27) provides single and double pulse
modulation with selectable pulse widths and periods or a user-definable pulse train.
See also
Chapter 5.5.1, "Overview of LF Generator"
External Modulation Sources
The modulation input MOD EXT at the instrument front provides the external modula-
tion sources for amplitude, frequency and phase modulation.
The external audio signal for stereo modulation is input via the analog L and R inputs
or via the digital S/P DIF interface at the rear of the instrument.
The external modulation signal for AM, FM and PM at the input must have a voltage of
U
S
= 1 V (U
EFF
= 0.707 V) in order to achieve the displayed modulation depth and
range. The input voltage should not exceed 1
V, otherwise modulation distortions might
occur.
The PULSE EXT connector at the rear of the instrument controls the external pulse
modulation. The input shows some hysteresis with threshold levels of 0.5
V/1.5
V. The
voltage must not exceed 5
V.
Simultaneous Operation of Several Modulations or Other Operating Modes
The table shows the modulations and operating modes which can be activated simulta-
neously (+) or which deactivate each other (-).
AM
FM
PhiM
Pulse
Amplitude modulation (AM)
/
+
+
(+)
Frequency modulation (FM)
+
/
-
+
Phase modulation (PhiM)
+
-
/
+
Pulse modulation (Pulse)
(+)
+
+
/
5.4.2 Amplitude Modulation (AM)
An internal and/or external source can be selected for amplitude modulation. The LF
modulation generator is available as the internal source.
Two-tone AM is possible by simultaneously switching on the external and internal
source.
The MOD EXT input connector for external feed of analog modulation signals is at the
front of the instrument. The coupling mode of the input (AC or DC) can be selected.
The AM modulation depth is limited by the maximum peak envelope power (PEP).
Modulation
