External FM Frequency Response

FM frequency response verifies 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.

Instrument

Critical Specifications for This Test

Recommended Model

Measuring Receiver

FM Deviation Accuracy

8902A

Digital Multimeter

 

3458A

Function Generator

 

33120A Opt 001, 33250A

 

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

FM Frequency Response Test Setup