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| Updated: Jan 30, '06
Click to check for program updates The color of each trace corresponds to the color of the label at the top of the Y-axis.
The most common commands use the buttons along the bottom edge of the screen: SCAN - Starts the frequency scan between the specified limits: Start_freq to the End_freq. (see Limits button below.) Each time the scan button is clicked, the graph is cleared and the new scan data replaces the previous data in memory. RESCAN - A new scan is started but the graph is not cleared. This makes it easy to see the before and after effects of changes to an antenna (or any discreet component being measured). The new data replaces the previous data in memory but both graphs can be viewed simultaneously. RESCAN can also be used to overlay new data on top of a scan that was loaded from a data file. See "File -> Load" below. RECYCLE - Scanning is repeated over and over until the RECYCLE or the HALT button is clicked. This makes it possible to continuously view the results while adjusting an antenna or tuning a stub. The resonant frequency is displayed above the graph and it's updated after each scan during recycle. The scan limits can be adjusted to narrow the scan range for a faster update rate. LIMITS - When this button is clicked, a dialog box pops up for entering the start and stop frequencies and the size of the frequency increment between measurement points. The start and stop frequencies range from 1MHz to 32MHz. For example, to scan the 40-meter band, you might enter 6.9MHz for the Start frequency, 7.4MHz for the Stop frequency and 0.01MHz for the frequency Delta (the spacing between measured points). This would result in a scan of 50 points across the band. The maximum number of scan points is 200 and the minimum number is 5. You don't have to worry about these details; the program will check the input data for reasonable values and adjust the frequency delta if necessary. Note that when using the cursor to read out numeric data (discussed in detail later), the displayed values are interpolated between the measured values. Therefore in some cases it may be desirable to use a larger frequency delta between steps for a faster scan rate. You can still read the parametric values at intermediate frequencies with the cursor. The scan rate is about 15 to 20 points per second, depending on the speed of the PC. The program can be run on older, slower computers with Windows 95 but the scan rate may be slower. SCALES - When this button is clicked, a dialog box pops up for entering the full-scale values for: SWR, Impedance_magnitude (Zmag), Theta and Return Loss. Theta is the phase angle of the load impedance. Return Loss is a negative number in decibels. If the actual measured value is off the scale (flat line at the top of the graph), the value readout by the cursor is still valid since it uses the raw data stored in memory. For example, you can set the Zmag scale to 500 ohms in order to see fine details but if the impedance actually goes up to 1500 ohms at some frequencies, the cursor can still read the true value and display it in the data window. CABLE - This command is used to measure several parameters related to the transmission line. A message box pops up to prompt that the cable should be either open or shorted at the far end for these tests to be valid. After this is ready, click OK to continue. Next, enter the Velocity Factor (typically in the range of 0.66 to 1.00). Next, enter the length of the cable if it is known. If zero is entered, the velocity factor previously entered will be used to calculate the length. If the length value is followed by the letter "M", the length will be considered to be in meters; otherwise, it's in feet. If the length is specified (greater than zero), then the velocity factor will be calculated and the value of velocity factor that was previously entered will not be used. Next, enter the frequency at which the cable impedance will be measured. Typically this value is in the band that you're most interested in. The cable wavelength will be calculated using this frequency and displayed with the "Measurement results". Some measurements are made and then a message box prompts to change the end of the line to the opposite condition: After the tests are complete, the results are displayed. SMITH - A window is displayed with a Smith chart showing a plot of the reflection coefficient versus frequency. As the cursor is moved with the mouse over the original plot, a marker dot is displayed at the corresponding point on the Smith chart and the relevant data is displayed in this window. COMMENT - A dialog box pops up for you to enter a comment that will be displayed at the bottom of the graph. This is very useful for documenting the test conditions. This comment will appear in a screen capture or a screen print and it will be saved in the raw data file on disk if this scan is saved. HALT - While the scan is in progress, you can stop it by clicking this button. This is different from the QUIT button (shown below). QUIT - This stops the program, saves the setup conditions (limits, scales, etc) and exits back to the Windows OS. When the program is launched again, the setup conditions and calibration data will be restored automatically.
FILE: Load - Load a raw data file for a previous scan. After this file is loaded its data is just like the original scan. The cursor can be used to readout the numeric values. When a data file is being displayed, the name of the file appears at the top of the graph. Save - Save the raw data for the last scan that was done. If you clicked the RESCAN button, the data that will be saved is for the last scan. Even though the earlier scan is being displayed on the graph, its raw data was replaced in memory by the new data corresponding to last rescan command. Print - Print the graph on the system printer. Quit - Stop the program and exit. This is the same as the QUIT button at the bottom of the screen. DATA: Measure point - Measure the impedance at a specified frequency. Data can also be sounded out in Morse code (see below). Constant Freq - output a constant frequency that can be used as a test signal. Initial frequency accuracy is +/-30ppm. At 1MHz, the output amplitude into 50 ohms is about 40mv-rms and somewhat less at higher frequencies. Measure Crystal - Measure the parameters of a quartz crystal automatically. SETUP: Plot Parameters - The parameters to be plotted on the graph can be selected. Calibrate Analyzer - calibrate the AIM430 using open circuit and short circuit conditions. The calibration data is saved in a disk file that's read each time the program is launched. Enter Zo - Enter the nominal impedance of the transmission line. This is used to calculate the SWR. This is a real number, no imaginary part. Cable Calibration - Properties of the cable are calculated and saved in files that are used when the "Refer to Antenna" mode is enabled. This involves taking two scans, one with the cable terminated by a small resistor (20-100 ohms) and another with it terminated by a large resistor (1K-2K). The data is saved in a file with a user-specified name. This data is recalled later when a measurement is refered to the antenna. Any number of cable data files can be saved in the same folder. Refer to Antenna - The impedance readings are transformed to be equivalent to readings directly at the antenna terminals. The cable properties are determined first using the "Cable Calibration" function shown above. The data file is selected first when this option is used. Comm Port - Enter the RS232 port used for communication. Port values can be 1,2,3 or 4. This is saved in the initialization file that's read each time the program is launched. Morse - Clicking enables/disables the Morse code output. Three values can be sounded out: Sxx.xx= SWR, Zxx.xx=Zmag, Txx.xx=Theta. The decimal point is coded as "R". This is active when the "Measure Point" function is used (see above).
AutoPwrOff - This button enables/disables the automatic power down feature of
the analyzer. The enable/disable flag is saved in the analyzer initialization data when you exit from the program (QUIT) and
restored each time the program is started again.
HELP: Help - Display the help file. About - Displays a message box with the version and date of the AIM430 programs in the PC and the microprocessor. HOT KEYS:
The following keyboard keys can be used
S - Scan (same as Scan button)
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