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20 N9069C Noise Figure Measurement Guide
Making Noise Figure Measurements
Making Frequency Converter Measurements
Making Frequency Converter Measurements
This chapter describes how to make noise figure measurements involving
frequency converters. Frequency converters are necessary when:
— The frequency conversion is part of the DUT. For example, the DUT is a
mixer or a receiver.
— The frequency conversion is part of the measurement test setup. The DUT is
to be measured at a higher frequency than the analyzer’s frequency range
covers, hence an external Block Downconverter and local oscillator are
added to the measurement test setup to convert this higher frequency to a
frequency within the analyzer's range.
The noise figure measurement application can support multiple frequency
conversions, in the DUT (including multi-stage converter) and/or as an added
System Downconverter, which configures the analyzer as a frequency range
extender. Refer to “Accounting for Frequency Conversion” on page 50 for
details about what needs to be considered carefully in the frequency converter
measurements.
Making Frequency Converting DUT Measurements
An example is provided on the following pages using the analyzer to make a
noise figure measurement on a downconverter, which is upper sideband. The
specifications for the DUT are listed in Table 2-2 on page 22 . The LO is set to
sweep in a frequency range and the IF is fixed at 60 MHz frequency.
The calibration of the measurement system is similar to a basic calibration, the
noise source is connected directly to the RF input of the analyzer and a
calibration is made. The DUT is then placed between the noise source and the
analyzer, and a corrected measurement is made. The DUT performs frequency
conversion in the measurement setup. However, there is no frequency
conversion in the calibration setup, as is shown in
Figure 2-3 on page 21
. The
purpose of the calibration setup is to allow the analyzer to measure its own
noise figure and sensitivity with the noise source. The calibration must be
performed across the frequency range to which the analyzer will tune when
performing the measurement.
If the DUT has a low or negative gain, it is recommended to use a USB
preamplifier together with the signal analyzer to get more accurate
results. For more details, refer to “Using the U7227-Series USB
Preamplifiers in Noise Figure Measurements” on page 37 .
The RF input section on the X-Series analyzers has a built-in 3.6 GHz Low
Pass Filter. This filter needs to be accounted for when planning the filter
requirements during calibration and measurement when working in low
band <3.6 GHz.