Internal Phase Modulation Distortion

ΦM distortion is expressed as the square root of the ratio of the power contained in the harmonics of the demodulated ΦM waveform to the power of the fundamental component of the demodulated waveform.

This is essentially a total harmonic distortion (THD) measurement and is made directly by the 8903B audio analyzer. The 8902A measuring receiver simply demodulates the ΦM signal and supplies a baseband signal (sine wave) to the 8903B input. The THD indicated by the 8903B includes the distortion added by the measuring receiver.

Instrument

Critical Specifications for This Test

Recommended Model

Measuring Receiver

FM Demodulated Distortion < 0.1%

8902A

Audio Analyzer

Distortion <±1 dB

8903B

 

Connections and Setup Procedures

All test equipment requires a 30 minute warm-up period to ensure accurate performance.

 

  1. Connect all test equipment as shown.

  2. Connect GPIB cables to all GPIB-controlled test equipment.

  3. While performing this test, follow all instructions on the controller display.
     

Measuring Receiver Calibration Setup

Phase Modulation Distortion Test Setup