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Distortion measurement with a Spectrum Analyzer(Part 2)
Release time :2017.12.17 Reading quantity:5 source:Salukirf, original

In this artical, harmonic components are measured of a signal with frequency of 1 GHz and power of -10 dBm generated by the signal generator.

1)       Set the output signal of the signal generator:

Set the frequency of the signal generator as 1GHz and power as -10dBm. Connect the output of the signal generator to the input port of the spectrum analyzer, as shown in Fig. below. Enable the ON state of the radio frequency.

1-spectrum analyzer pulse measurement.png

2)       Set the starting frequency and stop frequency of the spectrum analyzer.

l  Press [Reset] key.

l  Press [frequency], [Start Freq], 800[MHz], [Stop Freq] and 2.5[GHz].

As shown in Fig. 1, the fundamental wave and second harmonic will be displayed on the screen.

Fig.1 Input Signal and Harmonic.png

Fig. 1 Input Signal and Harmonic

3)       Set the video bandwidth to smooth noise so as to improve the resolution.

l  Press [Bandwidth], [Video Bandwidth Auto Man] to enable auto off.

l  Use [↓] key to reduce video bandwidth.

4)       In order to improve the measurement accuracy, set the peak level of the fundamental wave as the reference level.

l  Press [Peak] and [Peak Search], and read the peak power.

l  Press [Amplitude] and [Ref Level], and set it as the peak power. Results are shown in Fig 2.

Fig. 2 Setting of Signal Peak as Reference Level for Maximum Accuracy.png

Fig. 2 Setting of Signal Peak as Reference Level for Maximum Accuracy

5)       Activate the second marker.

l  Press [Delta], and [Next Peak].

In this case, the fixed marker is on the fundamental wave, while the mobile marker is on the peak point of the second harmonic, as shown in Fig.3

Fig. 3 Second Harmonic Measurement based on Marker Difference.png

Fig. 3 Second Harmonic Measurement based on Marker Difference

6)       Measure the harmonic distortion (Method 1).

The fundamental wave and the second harmonic as shown in the figure has am amplitude difference of about -60 dB, or a harmonic distortion of 0.1% (see Fig. 4).

Fig. 4 Conversion of Percentage of Harmonic Distortion Amplitude.png

Fig. 4 Conversion of Percentage of Harmonic Distortion Amplitude

To measure the third harmonic, press [Next Pk Right] and read the amplitude ratio of other harmonics to the fundamental wave.

7)       Measure the harmonic distortion (Method 2).

l  Press [Amplitude], [Units] and [Volt].

In this case, the unit of the differential marker will automatically change into volt. An easy way to determine distortion percentage is to change the unit to volt. Move the decimal of the proportion indicated by the differential marker rights for two places to obtain the distortion percentage. The minimum ratio that can be displayed is 0.01 or 1%.


Now Saluki has following 5 series of spectrum analyzers to fit all your need on spectrum measurements.

S3302 series handheld spectrum analyzer (9kHz -20GHz / 44GHz)

S3531 series spectrum analyzer (9kHz - 1.8GHz / 3GHz)

S3532 series spectrum analyzer (9kHz - 3.6GHz / 7.5GHz)

S3331 series handheld spectrum analyzer (9kHz - 3.6GHz / 7.5GHz)

S3503 series spectrum analyzer (3Hz - Max 50GHz)