R&S SMB Test Procedures
1407.0806.82 1.21 E-5
Residual FM
Test assembly Connect spectrum analyzer to RF socket of the DUT.
Test method The FM demodulator of the analyzer is used to FM-demodulate the
CW signal of the DUT. By setting the AF-low-pass and high-pass-
filters the RMS value in the desired bandwidth can be measured. The
v
alue displayed is the sum of the analyzer residual FM and the DUT
residual FM. Because they are uncorrelated, the displayed result is
worse than residual RMS of the DUT alone. Therefore, if the sum is in
tolerance according to the data sheet the DUT is also in tolerance.
Measurement Settings on DUT:
- frequency: 1 GHz
- Level: 0 dBm
Settings on analyzer:
- CENTER: 1 GHz
- REFERENCE LEVEL: 1 dBm
- FM DEMOD
- FM DEMOD MEAS TIME: 100ms
- FM DEMOD DEMOD BW: 200 kHz
- FM DEMOD AF-FILTER HIGH PASS AF FILTER: 300 Hz
- FM DEMOD AF-FILTER LOW PASS AF FILTER: 3 kHz
The Residual FM in the frequency range 300 Hz – 3 kHz is the
RMS value displayed.
Repeat the measurement with setting the HIGH PASS AF FILTER:
to 20 Hz and the LOW PASS AF FILTER to 23 kHz.
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