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57
A
3
- refers to third harmonic amplitude (V)
A
n
refers to n
th
harmonic amplitude (V)
If the signal amplitude is carefully measured as shown in the above example, the obtained harmonic distortion
percentage is accurate.
8
Pulse RF signal measurement
1) Definition of pulse RF signal
The pulse RF signal refers to a RF pulse string of the same repetition frequency and constant pulse width, shape
and amplitude. This section introduces several methods of measuring pulse RF signal parameters, including how to
measure the center frequency, pulse width and pulse repetition frequency. In addition, the measurement of peak
pulse power is also discussed.
The resolution bandwidth has great influence on pulse RF signal measurement. You must understand the
relationship between the resolution bandwidth and pulse repetition frequency. If the resolution bandwidth is
narrower than the pulse repetition frequency, only individual frequency components of the pulse RF signal will
appear on the screen. This is known as the narrow band mode. The mode in which the resolution bandwidth is
broader than the pulse repetition frequency is known as the broad band mode. In this case, you can see the
spectrum envelope formed by pulse segments that are equalized by the tested pulse repetition frequency.
2) Center frequency, side lobe ratio and pulse width measurement of pulse RF signal
a) Set the output signal of the signal generator:
Set the frequency of the signal generator as 1GHz and power as -20dBm. Connect the output of the signal
generator to the input port of the spectrum analyzer, as shown in Fig. 4-1. Set the repetition frequency of pulse
modulation as 1kHz and pulse width as 900ns. Enable the pulse modulation and RF output.
b) Set the spectrum analyzer:
The pulse RF signal is generally measured in the broad band mode. In order to prevent the influence of the video
filter on measurement results, the video bandwidth should be set as 3MHz.
Press [Reset] key.
Press [Frequency], [Center Frequency] and 1[GHz].
Press [frequency], [Span], 10[MHz], [sweep], [Sweep Time Auto Man] and 60[ms].
Press [BW], [RBW Auto Man], 100 [kHz], [VBW Auto Man] and 100 [kHz].