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 3-15 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 “Test Sequencing” located in Chapter 2.

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.

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:

nputting the network analyzer into tuned receiver mode

nsetting up a frequency list sweep of 26 points

nperforming a response calibration

nprompting the user to connect a mixer to the test set up

ninimg a loop counter value to 26

naddressing and configuring the two sources

ncalling the next measurement sequence

1.Make the following connections as shown in Figure 3-14. Set the HP-IB address of the external RF source to 19 and the external Ix) 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.

Note You may have to consult the User’s Guide of the external source being used to determine how to set the source to receive SCPI commands.

3.Be sure to connect the 10 MHz reference signals of the external sources to the EXT REF connector on the rear panel of the analyzer (a BNC tee must be used).

Note If the 10 MHz reference signals of the external sources are connected together, then it will only be necessary to connect one reference signal from one of the sources to the EXT REF connector of the analyzer.

Making Mixer Measurements 3-17

Page 159
Image 159
HP 8753E manual Fixed if Mixer Measurements, Tuned Receiver Mode, Sequence 1 Setup