2-27
Making Mixer Measurements (Option 089 Only)
Fixed IF Mixer Measurements
Fixed IF Mixer Measurements
A fixed IF can be produced by using both a swept RF and LO that are offset by a certain
frequency. With proper filtering, only this offset frequency will be present at the IF port of
the mixer.
This measurement requires two external RF sources as stimuli. Figure 2-22 shows the
hardware configuration for the fixed IF conversion loss measurement. This example
measurement procedure uses the analyzer’s test sequence function for automatically
controlling the two external synthesizers (with SCPI commands), and making a conversion
loss measurement in tuned receiver mode. The test sequence function is an instrument
automation feature internal to the analyzer. For more information on the test sequence
function, refer to "Using Test Sequencing to Test a Device" on page 1-114.
Tuned Receiver Mode
The analyzer’s tuned receiver mode allows you to tune its receiver to an arbitrary
frequency and measure signal power. This is only possible if the signal you wish to analyze
is at an exact known frequency. Therefore, the RF and LO sources must be synthesized and
synchronized with the analyzer’s time base.
Since the analyzer is not phaselocking in this configuration, you can use it to measure
conversion loss of a microwave mixer with an RF frequency range output.
Tuned receiver mode also increases dynamic range. Broadband techniques like diode
detection have a high noise floor, while narrow band techniques like tuned receivers are
much less susceptible to noise.
Sequence 1 Setup
The following sequence initializes and calibrates the network analyzer. It then initializes
the two external sources prior to measurement. This sequence includes:
• putting the network analyzer into tuned receiver mode
• setting up a frequency list sweep of 26 points
• performing a response calibration
• prompting the user to connect a mixer to the test set up
• initializing a loop counter value to 26
• addressing and configuring the two sources
• calling the next measurement sequence
1. Make the following connections as shown in Figure 2-21. Set the GPIB address of the
external RF source to 19 and the external LO source to 21.
2. Confirm that the external sources are configured to receive commands in the SCPI
programming language and that their output power is switched on.
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