Rohde & Schwarz SMB100A - Amplitude Modulation (AM)

Instrument Function
R&S
®
SMB100A
169Operating Manual 1407.0806.32 ─ 13
The external modulation signal 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 1.1 Vs, otherwise modulation distortions might occur. With external pulse
modulation, the switching point is max. 2.4 V and the voltage at the input should not
exceed 5 V. The maximum modulation frequency is 10 MHz for frequency and phase
modulation.
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) R&S SMB-K22 (+) + + /
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).
Exponentional AM (Instruments with 12, 20, or 40 GHz frequency options)
Besides the linear amplitude modulation, whereby the signal voltage is proportional to
the modulation signal, instruments equipped with the frequency options (R&S SMB-
B112(L) /-B120(L) /-B140(L)) in addition provide a level-proportional power or amplitude
modulation.
In this case, the R&S SMB exponentially distorts the modulation signal, before it is output
at the LF CONNECTOR - regardless of the AM Source Int, or Ext . The AM Depth is then
indicated in dB.
Signal Sources for Exponential AM
You can perform exponential AM using either the internal, or an external modulation
signal. However, in contrast to linear AM, the signal at the LF output connector is distorted
in any operating mode. AM Source Int+Ext is not available.
Modulation