Acquiring Agilent 8970B Noise Figure Measurement Data over the GPIB Bus and VEE Question: Is there an example program for acquiring data from the Agilent 8970B Noise Figure Meter via the GPIB bus? Answer: Yes. Here will be shown the components of a VEE program that will acquire frequency, noise figure, and insertion gain or loss from the Agilent 8970 Noise Figure Meter. The program was developed in the VEE graphical programming language. The programming concepts can be used with most other programming languages. The following screens provide views of the various components of the program. These components include a user interface panel, a main program, eight user objects, and a single user function. The user objects and function are invoked by the main program and are listed below in order of execution within the main program: 1. See this screen showing the "declare_variables" section: This is a variable declaration section where the variables start_freq, stop_freq, step_size and freq_incr are declared and set as global variables. 2. See this screen showing the "data_label" section: This user function builds a string which is utilized as the "Frequency Noise Figure Insertion Gain" label for the data display and file save. 3. See this screen showing the "Define Start/Stop/Step/Increment" section: This section of the program queries the user for input related to the setting of variables declared in the "declare_variable" user object. 4. See this screen showing the "SetUp SRQ" section: This user object clears both the SRQ and the Extended Status Bytes. The SRQ is then set to assert on the data ready or data available condition. 5. See this screen showing the "SetUp NF meter" section: The noise figure meter is commanded to display the insertion gain in the left window and the noise figure in the right display window. Next the Stop Frequency, Start Frequency, Step Frequency, and the Frequency Increment are all set. Once the user objects above are executed the program will execute the "Message Box" object which advises the operator to: connect the noise source directly to the noise figure meter; perform a LOCAL - CALIBRATE - CALIBRATE keystroke sequence; and then insert a device under test (DUT) between the noise figure meter and the noise diode. A measurement is then triggered via the command WRITE TEXT "T2" EOL. The program executes a REPEAT Until Break loop that repeatedly calls the following user objects: 6. See this screen showing the "Data Available Detect via SRQ" section: This user object will execute until bit 0 is set to a value of 1 indicating that the measurement data is available. The data is then read out of the noise figure meter in the form of frequency, noise figure, insertion gain or loss. This type of measurement complete sensing is critical to ensure the data captured has been fully averaged or smoothed. 7. See this screen showing the "last_equal_stop?" section: This user object ensures that the last measurement frequency matches the user defined stop frequency. 8. See this screen showing the "output_CSV_sep_data_to_file" section: This user object that prompts the operator for a file name to store the noise figure measurement data to. The data is output as comma separated data with the first line being a label to indicate frequency, noise figure and insertion gain or loss. 9. See this screen showing the "another test?" section: A simple user object that prompts the operator for another test or to exit the application. The DUT for this example was a 10dB coaxial attenuator.
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