Internal Phase Modulation Distortion

ΦM distortioni s 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.

Required Test Equipment

Instrument

Critical Specifications for This Test

Recommended Model1

Measuring Receiver

FM Demodulated Distortion < 0.1%

8902A

Audio Analyzer

Distortion <±1 dB

8903B
  1. Refer to the main equipment list for alternate models.

Connections and Setup Procedures
  • All test equipment requires a 30 minute warm-up period to ensure accurate performance.
  • In the following test setup, direct cable and adapter connections are designated as solid lines. Changeable cable and adapter connections are designated as dashed lines.
  • Connect all test equipment as shown.
  • Connect GPIB cables to all GPIB-controlled test equipment.
  • While performing this test, follow all instructions on the controller display.

 

Measuring Receiver Calibration Setup

Phase Modulation Distortion Test Setup