Rohde & Schwarz R&S SMU200A, Service Manual

Page: 74 / 294

Test Procedures R&S SMU200A
1007.9845.82 1.48
E-12
Broadband Amplitude Modulation
Test equipment - Spectrum analyzer (Table 1-2, item 24)
-
Signal generator (Table 1-1, item 5)
Test setup
Connect the RF output of the DUT to the spectrum analyzer, connect
the signal generator to the I input of the DUT.
Note:
If the measurement of the modulation frequency response has
been successfully performed for I/Q modulation, only a functional
test is required here.
Measurement Settings on DUT:
RF On
Frequency 1 GHz
Level 0 dBm, ALC State OFF
Broadband AM menu:
State On
Functional test: Setting on signal generator:
- Level 0.20 V (Vpeak) corresponding to -4 dBm for a modulation
depth of 80%
Vary the frequency from 1 MHz to 30 MHz on the signal generator
and measure the sidebands referred to the carrier at SPAN 3 MHz.
They should be 8 +- 1.5 dB below the carrier level.
Repeat the measurement at a frequency of 30 MHz on the signal
generator and SPAN 70 MHz on the analyzer. The sidebands should
now be 8 +-3.5 dB below the carrier level.
Complete measurement:
Setting on analyzer and measurement as for I/Q modulation,
modulation frequency response, but the level is first to be measured
as reference at the test frequency.
Since the sidebands have an offset of m/2 from the carrier, an offset
of -6 dB corresponds to 100% AM.
The modulation depth is calculated with the formula
m = 2*10
(sideband offset/20)
.
The frequency response is the difference between the greatest
and the smallest modulation depth.