The PK Antenna Analyzer

Transcription

1 The PK Antenna Analyzer Figure 1. The PK Antenna Analyzer, PKAA. The PK antenna analyzer (PKAA) is a low cost, full-featured instrument with many unique features: VSWR measurements covering all amateur bands continuous scans can be done for any frequency between 1-30MHz. Predetermined band edges for quick entry of scan start and end points all lower and upper band limits serve as default scan points, fully adjustable with a simply turn of the encoder Large (3 x 2 ) color TFT display for scan plots a 262,000 color display with 480x320 pixels. Compare to other higher-priced units with 128x64 resolution. Save scan data. An optional 2Gb SD card allows you to save over 9000 scans! Others only allow limited scans (e.g., 10) that are save in memory. Turn the machine off and they are lost. Not with the PKAA!

2 Scan data export. The scan data are saved in the popular CSV format and can be exported via the USB port for use in other programs (e.g., Excel, graphics package, text editor, etc.) Scan overlays. Run a scan and save it to the SD card. Now make a change to the antenna, and run another scan and immediately overlay the previous scan plot to the current scan plot to assess the impact of your change on the antenna. 100 scan point resolution regardless of scan spread compare to other analyzers that use only 12 scan points. Fast scans, typically less than 5 seconds for a 100 step scan compare to 30 seconds with fewer scan points other units. Portable use with 9V battery or use a 9V wall wart when grid power is available; perfect for in the field or home use. Simple two control user interface...and one of those is the power switch! Monitor the VSWR for a given frequency in real time...perfect for tuning mag loop antennas The rest of this manual details how to use your PKAA. Getting Started This section describe the process leading up to your first antenna scan using the PKAA. Connecting the Antenna The first step is to attach the antenna that is to be analyzed. The PKAA ideally should be connected to a 50 ohm antenna load using the unit's BNC connector. Because antennas are rarely a perfect 50 ohm load, the PKAA can tell you how much your antenna deviates from the ideal match. If your antenna uses a different connector (e.g., a PL-259), you can use a BNC-Male to SO-239 UHF-Female Coaxial Adapter Connector, or a similar cable adapter. Applying Power to the PKAA On the front of the analyzer, is a toggle switch that allows you to select powering the unit from the internal 9V battery or an external power source. If you wish to use an external power source, the source should supply 9V at approximately 300 (or more) milliamps via a standard 3.5mm barrel connector. The power switch is a double-throw type. The center position turns the unit off. There is no power indicator as the display is blank when no power is applied. If you toggle the switch upwards, the unit turns on using the internal 9V battery for its power source. If you toggle the switch downwards, the units expects a 9V external power source to power the unit. Turning the Unit Off When the unit is turned off by returning the power switch to the center position, any scan data that was not saved to disk is lost. This would also apply to any other power interrupts (e.g., dead battery, loss of

3 grid power, etc.). The Main Menu Figure 2 shows the Main Menu that controls the options and features of the PKAA. The Main Menu has Figure 2. The Main Menu options three menu choices: 1) Analysis, 2) Options, and 3) View Mins. The Options and View Mins also have submenus that are discussed later. Moving Among Menu Options Menu options are changed by rotating the encoder control located near the bottom-right corner on the front of the unit. A clockwise motion moves the highlighted selection field (e.g., a white background as seen for New Scan in Figure 2) to the right. A counter-clockwise motion moves the highlighted selection field, or selection indicator, to the left. The selection indicator is defined by its blue letters on a white background. If you are turning the encoder control clockwise and are at the last menu option (e.g., at View Mins), the section indicator wraps around to the first menu item (e.g., New Scan). If you are at the first menu item (e.g., New Scan) and turn the encoder counter-clockwise, the section indicator move to the last item in the menu (e.g., View Mins). This wrap-around feature makes moving between menu options quick and easy. Making a Menu Selection Once you have the section indicator on the menu option you wish to use, simply press on the encoder

4 control. The encoder control has a built-in switch that is activated any time you press on the control. Therefore, moving the selection indicator to the desired menu option and pressing on the encoder control selects that menu option. Analysis Menu Option The Analysis option is selected any time you wish to perform a new antenna scan, repeat a previous scan, or monitor the SWR for a given frequency. Move the selection indicator to the Analysis menu option and press on the encoder control. Shortly you are presented with a submenu that looks like Figure 3. (The screen will look a lot better because I'm a bad photographer.) The highlighted menu Figure 3. Analysis Submenu option in Figure 3 is New Scan. You would select this option whenever you wish to perform a new scan or change the scan parameters (e.g., the start and end frequencies for the scan). Press the encoder shaft to select the New Scan option. Another submenu presents a list of amateur radio bands, M, as shown in Figure 4. Each band option stores the start and end frequencies for that band and simplifies entering the scan data. Note: the bands are simply provided as a convenience by presenting default start and end scan frequencies. You can perform a scan outside these bands if you wish to do so, provided it does not exceed the upper-limit scan frequency of approximately 30Mhz.

5 Figure 4. The New Scan submenu of Amateur Band Frequencies Submenu Choice Let's assume you wish to run a scan on a 40M antenna. In this instance, the submenu is organized in an up-down fashion. Turning the encoder clockwise move the selection indicator downward. Rotating the encode counter-clockwise moves the selection indicator upward. The same wrap-around feature applies to this and all other menus and submenus. Turn the encoder to the 40M option and press the encoder switch. This action presents the start-end scan input sequence. This can be seen in Figure 5. You are prompted to enter the starting scan frequency (start:). Because you selected the 40M option, the program defaults to the lower edge of the US 40M band, or 7000 KHz. If you turn the encoder shaft counter-clockwise one detent, the start frequency would change to 6900 Khz. If you turn it clockwise, it would advance to 7100 Khz. Each detent of the encoder changes the frequency by 100KHz. You can select a starting frequency outside of the normal band limits. When you have the desired start frequency entered, press the encoder switch. (I selected 6900 Khz.) This advances the selection indicator to the end: field, which defaults to 7300.

6 Figure 5. Entering the Start and End Scan Frequencies. Now enter the ending scan frequency, using the same means as you did for the starting frequency. You can enter a frequency above the normal band limit. When you press the encoder switch, the analyzer immediately begins calculating the VSWR for the frequency scan limits you entered. Figure 5 shows the display after the start and end scan frequencies of Hz have been set by the user, although I changed the 7300to 7400 to show that you can run a scan outside normal band frequencies. If you can't operate outside the band limits, why make them available? The reason is because, when you build a new antenna, it's quite possible (likely?) that the point of resonance will be outside the band limits on your first scan. By being able to plot where that resonance point is, you can shorten or lengthen the antenna to move it towards resonance within the band limits. Scan Plot When the scan is completed, the software immediately displays a plot of the data from the scan. Each scan will look similar to that shown in Figure 6, but with differing frequency data. We elected to set the maximum VSWR (SWR from now on) to 3.0. While operating with an SWR of 2.0 or less is desirable, anything above that SWR should be avoided if possible. For that reason, we decided to chop the maximum SWT in the plot to 3.0. Note in Figure 7 that the SWR is likely higher than 3.0 for frequencies below about 6.95MHz and above 7.37MHz. The scan plot shows the SWR for the range of the scan frequency you entered earlier. If you take the scan limits and figure the difference between them and divide by 100, you'll derive the frequency spread between scan points. This is because we always calculate 100 scan points for each plot. The time from entering the ending scan frequency to viewing the scan plot is typically less than 5 seconds. At the top of the plot you are given the minimum scan SWR and its associated frequency. This can be very useful when adjusting the antenna. You are also give a visual indicator of the approximate minimum scan position using a '+' symbol in red on the plot. You can also get an approximation of the usable bandwidth for the antenna by observing the frequencies that are at or below an SWR of 2.0. In Figure 6, it appears that the usable bandwidth spans from about 7.050MHz to 7.280MHz.

7 Figure 6. A Sample Scan Plot. Note: After a scan, the SWR and its attendant frequency data are held in memory until another option is selected or power is lost. This feature is important if you plan on doing overlay plots or saving the scan data to the SD disk. Repeat Submenu Option If you select the Repeat menu option (see Figure 3), a new scan is performed, but using the same start and end frequency as the most-recent scan. This is useful when you are tweaking an antenna for a set of frequencies and don't want to keep entering the band and frequencies between scans. The output is the same as Figure 6, but using the new data from the (modified?) antenna. Frequency Submenu Option This option is used when you wish to continually test the SWR at a specific frequency. For example, a mag loop antenna usually requires adjusting the tuning capacitor each time there is a small change in frequency. With this option, enter the desired frequency using the band selecion option (Figure 4) and the start frequency (Figure 5). Because you are only monitoring a set frequency, you do not need to enter an ending frequency. The program then begins to continuously report the SWR for that frequency. When you are finished tuning the antenna, press the encoder switch to terminate the frequency monitoring.

8 Options Menu Option The Options menu presents a list of actions that you can perform next. This option list is shown in Figure 7. Save Scan Submenu Option The first submenu option is Save Scan. This option can only be run immediately after you run a new scan. Recall that the PKAA saves the most-recent scan data in memory. If any menu option, other than Save Scan, is performed, the previous scan data are lost. Therefore, if you wish to preserve the mostrecent scan data, you should select the Save Scan option immediately after the scan plot is displayed. Push the encoder switch to activate this submenu choice. Once you press the encoder switch, the rest of the file saving process is accomplished without further input from you. Figure 7. The Options Menu All saved scan files begin with the name SCAN. The software then finds the last file saved, determines its file number (e.g., SCAN5.CSV as seen in Figure 8), increments the scan number by 1 and writes the data to the new file named SCAN6.CSV. The software tells you the name of the file and displays the message: File named SCAN6.CSV successful if the file is written to the SD disk. If the write fails, you are given an error message telling you the file was not stored on disk. The most likely reason for seeing an error message is that you did not place a micro SD card in the SD card slot on the back of the TFT display. The Micro SD Card Size The SD card hardware on the TFT display does not support cards with storage capability larger than

9 2Gb, so there's no point in buying a card larger than that. However, most larger micro SD card will work with the display even though the hardware cannot use the additional storage. You may have to do a little trial-and-error with larger SD cards. View Plot Submenu Option The View Plot submenu option is used when you wish to view a scan plot that has been previously saved to the micro SD card. When you select this option, the display presents you with a list of the currently-stored scan files, as seen in Figure 8. Use the encoder to move up and down through the list, moving the selection highlight to the file you wish to view. Once the file is highlighted, press the encoder switch. The software opens the selected file and displays the data stored in the SD card file. The resulting plot will be similar to the display seen in Figure 6. Figure 8. Select a Micro SD File View Table Submenu Option This option simply presents the plot data in numeric form rather than as scan plot. The data for the table is read from a selected SD file using the same selection process described in the View Plot option

10 discussed earlier. A typical run can be seen in Figure 9. First, notice that the table shows its first plot value as 3.15 at the frequency of The first number is the SWR number and the second is its associated frequency expressed in MHz. (The table view also lets you see values where the SWR is above 3.0.) Also note the orientation of the data: the data are presented across and then down. That is, the next data point in the table is the second set of data (i.e., 3.14, ) on the top line of the table. This was done to make better use of the pico acres of the display. It minimizes the need to scroll the data through all 100 scan points. Figure 9. Table View Submenu Option Overlay Submenu Option This option allows you to overlay the currently-active scan plot (i.e., the plot data currently stored in memory) with one that you have previously saved to the micro SD card. This is very useful when you are adjusting an antenna and would like to see what the latest adjustment did to the SWR measures. To activate this option, move the selection highlight to the Overlay option and press the encoder. You are now presented the Select File screen (see Figure 8) to select the earlier scan that you saved to disk. Once you select that file, the software plots the contents of the selected file and the plot data that are currently stored in memory. A typical overlay plot can be seen in Figure 10.

11 Figure 10. Overlay Plot Serial Submenu Option This option allows you to write the contents of the CSV scan data file to the PKAA USB port. A CSV (Comma Separated Variables) file is a standard file format that contains ASCII data, broken into fields where each variable is separated by a comma and each record is delimited with a newline ('\n') character. Most software programs (e.g., Excel, MySQl, etc.) can import such data files directly. You will need a program to accept the CSV data from the USB port (e.g., Telnet). If you do not have a USB reader-type of program, you can remove the micro SD card from the TFT display card slot and use a micro SD reader. Once the file is imported, you can manipulate that data as directed by your software. Delete Submenu Option This option is destructive. That is, once you delete a scan CSV data file, it is gone. (In theory you could recover it with a disk editor, but we wouldn't count on it.) Use this option carefully. Once you select this option, you are presented the same file selection submenu seen in Figure 8. Select the file you wish to delete by moving the selection highlight to the file to be deleted. Once the file is selected, press the encoder switch. The file is then deleted. When should you delete a scan file? It's up to you, but it gets tiresome scrolling through files that eventually become woefully out of date. Our preference is to delete unneeded files when the count exceeds 10 to avoid unnecessary scrolling. At the present time, the software is limited to 9,999 scan files even though the SD card will still have unused disk space. The reason is because the FAT file

12 names cannot exceed 8 characters under the current SD library code. Therefore SCAN9999.CSV is the last file name that can be accommodated. This ends the Options submenu option. View Menu Option The purpose of this option is to let you observe the minimum SWR's that have been recorded during all of your scan activity. This can be informative when you have one antenna performing on multiple bands. For example, a long wire antenna might be used on all bands but clearly will perform differently on the individual bands. If you run scans on each band, each scan records the minimum SWR figure for that band and writes it to EEPROM memory stored in the PKAA. This option provides a way to view those minimums. Submenu Options The submenu options look similar to the submenu seen in Figure 2, except the first submenu option in the list is All. If you select the All submenu option, you are presented a list of all of the recorded minimum SWR's that have been run. A typical display using the All submenu option can be seen in Figure 11. The All Submenu Option Figure 11. Note that the 10M bar does not plot a minimum SWR bar nor does it display the SWR value

13 at the end of the bar. The N/A simply means that no scan has been performed on the 10M band. You can also elect to display the bar graph for a single band by making a submenu selection of the band of interest rather than All. The bar graph is identical to those shown in Figure 11, but without any of the other (non-selected) bands. This completes the PKAA User's Manual directions.