External FM Frequency Response

FM frequency responseverifies that a selected FM deviation remains constant within ±1 dB as the FM rate is varied from 80 Hz to 100 kHz and the DUT CW frequency is varied from 500 MHz to 1.0 GHz. If the DUT meets the frequency response specification in this CW frequency range, frequency response in all other frequency ranges will be assured.

FM deviation is set to 100 kHz at an FM rate of 1 kHz. The actual deviation is measured with a measuring receiver and stored as the reference deviation. While the deviation setting remains at 100 kHz, actual deviation is measured for FM rates between 80 Hz and 100 kHz. If the measured deviation at any test rate is more than 1 dB different from the reference deviation at 1 kHz, the test fails. Each frequency is tested with this sequence:

  1. A reference signal is measured.

  2. The set deviation is measured for each applied rate change.

  3. Each deviation measurement is compared to the reference deviation.

The comparison is a calculation of the difference in the deviations relative to the reference rate. The relative value is the FM frequency response.

Required Test Equipment

Instrument

Critical Specifications for This Test

Recommended Model1

Spectrum Analyzer

FM Deviation Accuracy

E444xA2 Opt 1DS, 1233

Function Generator

  

33250A

Digital Voltmeter

  

3458A Opt 002
  1. Refer to the main equipment list for alternate models.
  2. Depending on your frequency range needs, choose either an E4440A, E4443A, E4445A, E4446A, or E4448A. (E4447A is for Power Level Accuracy adjustment only.)
  3. Options 1DS and 123 are for ESGs > 3 GHz.

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

FM Frequency Response Test Setup