Residual FM

Residual FM is unwanted frequency modulation of the ESG CW output.

The 8902A measuring receiver measures the deviation (in Hz) of the residual FM. Because the display resolution of the measuring receiver is not high enough to discern low deviations (i.e., low residual FM), the FM deviation signal from the 8902A is passed along to an audio analyzer, where the AC level is measured.

The 8902A FM deviation output level is 1 mV per Hz of deviation.

The measuring receiver has an internal L.O. to down-convert the RF Input to its 1.5 MHz I.F. Unfortunately, this internal L.O. does not have optimum phase noise for a residual FM measurement. For this test, the carrier signal is externally down-converted to 1.5 MHz and injected into the I.F. input of the measuring receiver.

 

Instrument

Critical Specifications for This Test

Recommended Model

Measuring Receiver

FM Demodulated Residual FM ≤ 0.1%

8902A

Audio Analyzer

AC Level Accuracy:   ± 3% 0.3 mV to 50 mV

Display Resolution:    0.01 mV

8903B, Opt 011 or 051

Local Oscillator

The 8663A and E8663B Opt 503 can only be used with ESGs with frequency range <4 GHz. The E8663B Opt 509 can be used with all ESGs.

Frequency Range:      100 to 4000 MHz

Residual FM

E8241A
E8244A
E8251A
E8254A
E8247C
E8257C
E8257D
E8267C
E8267D
8663A
E8663B

Mixer

RF/LO Freq. Range:   1 to 2800 MHz

IF Frequency Range: 1.5 MHz

RF/LO Freq. Range:   500 to 9000 MHz

IF Frequency Range: 50 MHz

M/A-COM MDC-174

M/A-COM MDC-164

 

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.

 

  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

 

Residual FM Test Setup

In Case Of Difficulty

The actual Residual FM is the sum of the Residual FM in all components in the measurement system. Ensure that the Local Oscillator and Measuring receiver are not contributing excessive residual FM to the measurement. For example, make sure they are meeting their specifications.