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In this case, the amplitude reading of the noise marker is correct, as the averages of all points are at the same
frequency, which is not affected by the shape of the resolution bandwidth filter. The noise marker is calculated
based on the average of the interested frequency points. The power of discrete frequency points should be
measured in the zero span mode, with the spectrum analyzer tuned to the interested frequency point.
7 Distortion measurement
Mutual interference between equipment in common in crowd operating environment of the communications system.
For example, second-order and third-order intermodulation distortion is common in narrowband systems. When
there are two signals (F
1
and F
2
) in one system, they and second harmonic distortion signals generated by them
(2F
1
and 2F
2
) mix and become third-order intermodulation products 2F
2
-F
1
and 2F
1
-F
2
very close to original signals,
thus resulting in high-order intermodulation distortion. Such distortion products are mostly generated by devices
such as amplifiers and mixers in the system. Most transmission units and signal generators have harmonics and
their components need to be measured.
1) Identification of distortion generated by spectrum analyzer
In the case of large signal input, the spectrum analyzer may be subject to distortion, which will affect the distortion
measurement results of true signals. You can set the attenuator to determine which signal is a distortion signal
generated by the spectrum analyzer. This example shows whether the spectrum analyzer is subject to harmonic
distortion based on the input signal.
a) Set the output signal of the signal generator.
Set the frequency of the signal generator as 200MHz and power as 0dBm. Connect the output of the signal
generator to the input port of the spectrum analyzer, as shown in Fig. 4-1. Enable the ON state of the radio
frequency.
b) Set the center frequency and span of the spectrum analyzer.
Press [Reset].
Press [Frequency], [Center Frequency] and 400[MHz].
Press [frequency], [Span] and 500[MHz].
You can see on the trace of the spectrum analyzer that the harmonic distortion of the signal is subject to 200MHz
deviation from the original 200MHz signal, as shown in Fig. 4-11.
c) Set the center frequency of the spectrum analyzer at the first harmonic distortion location.
Press [Peak] and [Next Peak]