User`s guide

296 Agilent E5505A User’s Guide
11 AM Noise Measurement Fundamentals
Method 2: Double-Sided Spur
Method 2, example 1
Advantages
• Requires only one RF source (DUT)
• Calibration is done under actual measurement conditions so all
non-linearities and harmonics of the AM detector are calibrated out. The
double-sided spur method and the single-sided-spur method are the two
most accurate methods for this reason.
Disadvantages
• Required that the DUT have adjustable AM which may also be turned off.
• Requires the AM of the DUT to be extremely accurate; otherwise a
modulation analyzer, for manual measurement of AM sidebands is required.
Procedure
1 Connect circuit as shown in Figure 227, and tighten all connections. If the
N5500A Option 001 or N5507A is available, use one of the connection
diagrams described in “AM noise measurement block diagrams" on
page 287.
2 Measure the power which will be applied to the AM detector. It must be
between 0 and +23 dBm.
3 Measure the carrier-to-sideband ratio of the AM at the AM detector’s input
with an RF spectrum analyzer or modulation analyzer (Figure 228 on
page 297). The source should be adjusted such that the sidebands are
between –30 and –60 dB below the carrier with a modulation rate between
10 Hz and 20 MHz.
Figure 227 Double-Sided spur AM noise setup (method 2, example 1)
DUT
AM detector
Noise
input
Test set