Configuring the Internal Baseband Source
R&S
®
SMW200A
410User Manual 1175.6632.02 ─ 30
Example: To calculate the maximum frequency offset
This example uses the following signal:
●
Standard: "Baseband > Custom Digital Modulation"
●
"Set according to Stanard > WCDMA-3GPP"
●
"Symbol Rate = 3.84 Msym/s" (3.84 MHz)
●
"Filter > Root Cosine"
●
"Roll Off Factor = 0.22"
The complex useful bandwidth of filtered signal is calculated as follows (see "Impact of
the Filter Parameters" on page 248):
●
f
use
= (1 + "Roll Off Factor") * "Symbol Rate"
●
f
use
= (1+ 0.22) * 3.84 MHz = 4.6848 MHz
For an instrument with a total available I/Q bandwidth of 160 MHz, the valid range of
values for the frequency offset is then:
●
-160 MHz/2 + 4.6848 MHz/2 ≤ f
offset
≤ 160 MHz/2 - 4.6848 MHz/2 or
●
-77.6576 MHz ≤ f
offset
≤ 77.6576 MHz
To observe the effect of offsetting the frequency
Use the built-in real-time graphical display ("System Configuration > Graphics > Power
Spectrum") and observe the power spectrum of the signal with and without frequency
offset:
●
See Chapter 3.3.6, "Verifying the Generated Signal", on page 69.
●
See "To set and verify a baseband frequency offset" on page 613.
5.14.1.2 Impact of the Phase Offset
The "Phase Offset" determines the phase offset between the different baseband sig-
nals. A phase offset rotates each point of an I/Q constellation diagram by the specified
phase offset.
Figure 5-34: I/Q constellation diagram: Effect after offsetting the phase by an angle of 45
°
Shifting and Boosting the Baseband Signal
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