Analog modulations
R&S
®
SMA100B
83User Manual 1178.3834.02 ─ 09
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The external modulation signal must have a voltage of US = 1 V (UEFF = 0.707
V) to achieve the displayed modulation depth and range.
Note that the input voltage does not exceed 1 V, otherwise modulation distortions
can occur.
For more information, see data sheet.
Interactions and characteristics
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FM and PhiM modulations exclude each other and cannot be performed simultane-
ously.
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In sweep mode, LF frequency sweep is possible.
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The settings of the modulation signal affect all analog modulations that use an
internal modulation source.
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You can feed an external LF signal in each of the two paths.
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Considerations to AM when using an external modulation signal:
If external modulation is enabled, the RFoutput amplitude follows the external mod-
ulation signal with a scaling factor defined by the modulation sensitivity setting.
With Coupling (AC/DC) > DC, the RF output signal behaves according to:
– input signal = 0 V: the RF output amplitude corresponds to the level value set in
the R&S SMA100B
– input signal = +1 V: the output level increases up to the maximum value given
by the set modulation sensitivity
– input signal = -1 V: the output level decreases down to the minimum value
given by the set modulation sensitivity
With Coupling (AC/DC) > AC, the modulation input signal is internally highpass fil-
tered. Therefore, the DC content of the input signal is removed before it reaches
the amplitude modulator.
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Using exponential amplitude modulation with an external source, sets the coupling
of the corresponding input automatically to DC.
See also Chapter 5.4.7.2, "Source > external settings", on page 117.
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Scan AM
– Scan AM provides the scan mode, i.e. an amplitude modulation depth with an
extended dynamic range that automatically uses the exponential amplitude
modulation type.
– If you use Scan AM with an external modulation input signal, the voltage range
is adjusted to +/- 6 V (usually +/-1 V). Therefore, we recommend that you do
not use the external modulation signal for FM or PhiM in parallel, since the volt-
age affects the modulations.
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The amplitude modulation types linear and exponential derive the carrier signal
either linear in percent / volt, or as complex exponential in dB / volt.
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For pulse modulated signals, you can select between fast or smoothed transitions,
see "Transition Type" on page 86.
This setting is available over the entire frequency range for all instruments with fre-
quency options up to 6 GHz. For higher frequency options, the frequency range for
the smoothed setting is limited.
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Chirp modulation
Modulation types and signal sources
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