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RF harmonic distortion measurement basics

This page covers RF harmonic distortion measurement. It includes test tools, test equipments and test procedure for the measurement of RF harmonic distortion.

harmonic distortion

When any input frequency signal is applied to the nonlinear device, it will generate unwanted frequencies other than the input signal. This unwanted frequencies if present at integer multiple of input frequency then they are referred as harmonics. Figure depicts harmonics(i.e. 2fc), which is at twice of input frequency (fc). Refer harmonics definition.

Test Tools or Test Equipments Needed

Following test equipments are needed for the harmonic distortion measurement setup.
• RF Spectrum analyzer
• RF Power Meter
• Device Under Test (DUT)
• RF signal generator or CW source
• RF Attenuator (Fixed or variable)
• RF Directional Coupler

Test Procedure for RF harmonic distortion measurement

RF harmonic distortion measurement

Following test procedure can be used for the measurement of harmonic distortion:

➨Do the setup as shown in the figure-1.

➨Feed the CW frequency (say 'Fc') to the nonlinear DUT (either RF Transceiver or RF Power Amplifier).

➨Connect the RF attenuator at the output of DUT and feed the signal output to the directional coupler.

➨Connect one port output of directional coupler to the RF power meter and the other port to the RF spectrum analyzer.

➨Place the markers at point 'P', point 'P1' and point 'P2'. P is the reference center frequency(Fc), P1 is the first harmonics at 2*Fc and P2 is the second harmonics at 4*Fc.

➨Difference between power levels at P and P1 will provide first harmonic distortion measurement. Difference between power levels at P and P2 will provide second harmonic distortion measurement.

➨It is measured in dBc. Greater the difference between the points better is the system.

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