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The main window Launching the program, the main window is presented:
Different areas can be identified:
The command area of the main window allows user to select the START and the STOP frequency, the sweeping mode and to run the measuring cycle.
Click it, the program will present the value without the "decimal" separators, enter the new frequency in Hz. Press the "TAB" key or click anywhere in the window, program will verify that the new value can be accepted and will present it formatted. The START frequency is the frequency always generated by the DDS, if you want to use the sweeper, as a fixed generator, just enter here the frequency you want to output. When the program is launched the generator is activated, a reset command is issued to the DDS, and the device is initialized to the START frequency. Every time the START frequency is changed, the appropriate command is addressed to the DDS forcing to generate the new frequency. The STOP frequency can be less or greater than the START frequency. The sweeping run will always begin at the START frequency and the output will be increased or decreased until the STOP value is reached. Then cycle restarts. The SWEEP ON button starts the sweeping run. The number of steps managed by the program is 400 per each cycle, resolution is 1 Hz. Before to initialize the cycle, the program tests that the difference between the START and the STOP frequency is at least 400 Hz, in case of error request to select new frequencies is presented.
While the SWEEP ON button is pressed his label is changed to SWEEP OFF. Press it again will stop the sweeping process. Three sweeping modes are available:
Sweeping modes are available only when the h/w is interfaced via the parallel port. This is the area where the output of DUT is plotted.
When the sweeping cycle is running the program reads back from the AD/C the 400 samples per cycle and real time plots them on the screen. Different scales can be selected for the Amplitude Y axe:
"SetUp/Preference" menu allows forcing the pointer to follow the path of the graph (white crossing lines) when moved. The analysis of the graph can be also done with the help of markers. Select the "View/Marker" from the menu or press the button "Marker". The program presents the position of 4 markers: 2 for the Frequency axe (blue vertical lines) and 2 for the Amplitude axe (blue horizontal lines). The value of the "Frequency" and "Volt/dB" of each marker are shown in the "Marker" windows Position the marker moving the cursor over the graph then press the mouse button:
or click over the field "Frequency" for the marker M1 and M2, "Volt/dB" for the marker M3 and M4 and enter the new value. Two auxiliary windows (menu "View/AUX1" and "View/AUX2") allow interfacing:
Command buttons were created here to manage the attenuator circuits that control the output of the DDS unit and the input from the AD/C. The I2C standard protocol has been also implemented, this can interface several devices like digital potentiometers that are useful to control the gain of a linear amplifier. The auxiliary command windows are very flexible and can be fully personalized, via the "SetUp/Configuration" menu. It is possible to assign to the windows any title like "Generator out" or change the description of the buttons and their values. The Configuration paragraph details the different options available.
8 output lines are connected to the 8 buttons (see the Hardware Interface paragraph), in order to drive 8 on/off devices. The original design was focused to drive a couple of digital attenuators (Macom AT200, 4 bits, DC to 2GHz, 30dB att.) or an array of solid state rele.
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