Internal FM Distortion

(E8257D/E8267D/E8663D Option UNT without H5K, and E8257N Only)

FM distortion is defined as the square root of the ratio of the power contained in the harmonics of a demodulated FM 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 a spectrum analyzer with analog demodulation measurement application or an 8903B Audio Analyzer. The THD indicated includes the distortion added by the measuring receiver in demodulating the FM signal from the DUT.

This test is currently performed in only one frequency band. Due to the signal generator’s design, this band is also representative of the signal generator’s full frequency range.

Equipment Setups

This test supports two equipment setups using either a spectrum analyzer or a measuring receiver. The spectrum analyzer is the preferred solution.

Preferred solution

A spectrum analyzer with analog demodulation measurement application is used to demodulate the signal and measure the deviation.

Test Equipment

Recommended Models

Alternative Models

Spectrum Analyzer

N9030B Opt 5xx1, N9063EM0E Analog Demodulation Measurement application

N9030A2 Opt 5xx1, N9063EM0E Analog Demodulation Measurement application

E444xA3 Opt 233 Measuring Receiver Personality

Select any option of PXA spectrum analyzer (503, 508, 513, 526, 543, 544, 550) that has a maximum frequency greater than or equal to the maximum frequency of the unit under test. The N9030A/B Option 550 is required for units with Option 567. The N9030A/B Option 550 frequency range is adequate for all PSG-D frequency configurations.
To use the PXA N9030A with N9063EM0E Analog Demodulation Measurement application functionality above 3.5 GHz, the N9030A must be upgraded with either Option MTU or TES. Refer to the section in the Required Test Equipment topic.
Select any model of PSA spectrum analyzer (E4440A, E4443A,E4445A, E4446A, E4447A, E4448A) that has a maximum frequency greater than or equal to the maximum frequency of the unit under test. An E4448A is required for units with Option 567. The E4448A frequency range is adequate for all PSG-D frequency configurations.

Alternate solution

Alternatively, an 8902A measuring receiver is used to demodulate the signal and measure the deviation.

Test Equipment	Recommended Models
Measuring Receiver	8902A
Audio Analyzer	8903B

Connections and Setup Procedures

All test equipment requires a 30 minute warmup period to ensure accurate performance.
In the following test setup, cables are designated as solid lines and direct connections are designated as dashed lines.
This performance test has a smart connection feature.

Connect all test equipment as shown.
Connect GPIB cables to all GPIB-controlled test equipment.
While performing this performance test, follow all instructions on the controller display.

Spectrum Analyzer Test Setup

Setup for Internal FM Distortion

Measuring Receiver Test Setup

Setup for Measuring Receiver Calibration

Setup for Internal FM Distortion

In Case of Difficulty

If this performance test fails, perform the following steps in order:

Check the equipment setup (see above). If the setup is incorrect, make the necessary corrections and rerun the Performance Test.
If this test fails with the equipment set up properly, refer to the troubleshooting section of the signal generator's service guide. If you do not have a printed copy of the service guide (Option OBW), one is available either on the CD-ROM that came with your signal generator shipment or on the Keysight Website.
If you cannot correct the problem using the troubleshooting procedures in the Service Guide, obtain service from Keysight Technologies. Refer to Contacting Keysight Technologies.