Agilent Technologies N9010A, Руководство пользователя

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106 Chapter 14
Baseband I/Q Inputs (Option BBA) Measurement Concepts
Baseband I/Q Measurement Views
Baseband I/Q Measurement Views
Measurement result views made in the IQ Analyzer (Basic) mode are
available for baseband signals if they relate to the nature of the signal
itself. Many measurements which relate to the characteristics that
baseband I and Q signals have when mixed and upconverted to signals
in the RF spectrum can be made as well. However, measurements
which relate to the characteristics of an upconverted signal that lie
beyond the bandwidth available to the Baseband I/Q Input circuits can
not be measured (the limit are dependent on the installed options:
Standard – 10 Hz to 20 MHz, Option B25 – 10 Hz to 50 MHz, and
Option S40 – 10 Hz to 80 MHz).
At RF frequencies, power measurements are conventionally displayed
on a logarithmic vertical scale in dBm units, whereas measurements of
baseband signals using Baseband I/Q inputs may be conveniently
displayed as voltage using a linear vertical scale as well as a log scale.
Spectrum Views and 0 Hz Center Frequency
To view the Spectrum display of I only or Q only signals, use the
Complex Spectrum measurement capability in IQ Analyzer (Basic)
Mode.
I only and Q only Spectrum views are conventional, displayed with 0 Hz
at the left side of the horizontal axis. When upconverted or multiplied,
an I only or Q only signal could ultimately lie above or below the carrier
center frequency, but in either case it will only occupy half the
bandwidth.
Waveform Views for Baseband I/Q Inputs
For Waveform measurements, two displays are available for baseband
I/Q input signals; the I and Q Waveform view, which separates the
individual I and Q traces, and the RF Envelope view.
Waveform Signal Envelope Views of I only or Q only
To view the Signal Envelope display of I only or Q only signals, use the
Waveform measurement capability in IQ Analyzer (Basic) Mode.
The I and Q Waveform of an I/Q signal is very different from the
complex signal displayed in the RF Envelope view. That is because the
RF Envelope is a product of both the I and Q modulation waveforms.
However, an I and Q Waveform measurement of an I only or Q only
signal is exactly the same signal displayed in the RF Envelope view.
That is because an I only or Q only waveform determines the I only or Q
only signal envelope. Thus, the RF Envelope view can be used to