Short Dipole & Horizontal Loop for 3.5 - 30 MHz

A recurring discussion topic during our morning QSOs involves two of the multi-band HF antennas presented in the article Choosing the Correct Balun, by W8JI. The antennas are:

• Multi-band Dipole / Doublet - described on pages 7-10
• Horizontal Loop - described on pages 16-19

The focus of our discussions has been on versions of these antennas that are sized for 3.5 - 30 MHz. To gain some additional insights about how these antennas compare, I modeled each with antenna analysis software. I used a height of 70 ft above average ground conditions, to be consistent with some of the data presented by W8JI. The following PDF documents present the analysis results:

• Radiation Patterns
• SWR and Impedance

The radiation pattern graphics show only the total gain views. The software can also present the gain views for horizontal polarization or vertical polarization separately. I limited the radiation pattern analysis to the 80, 40, 20, 15 and 10 m bands, but any frequency can be entered to generate any desired patterns. Would anyone like to see what the patterns look like for an 80 m loop on 1296 MHz?

The SWR and impedance results cover the full range from 3.5 to 30 MHz. The last page shows the impedance for selected frequencies within the ham bands. Only the points are plotted on that graph.

Further analysis will compare the SWR and impedance results for 300 ohm and 450 ohm feedlines. I believe that the software can also provide an overall efficiency figure for the combination of feedline and antenna.

Update 7/4/15: Below is a graph of impedance (for the shortened dipole) calculated at selected frequencies within the HF ham bands (3-30 MHz). These points are for the transmitter end of a 300-ohm feedline for 3 different lengths: 1/8 wavelength, 1/4 wavelength and 3/8 wavelength (at 3.5 MHz).  The 1/8 and 3/8 wavelength cases correspond to the recommendations of the W8JI article referenced above.  I was a bit surprised at the high impedance values for the 3/8 wavelength case in the 75/80 m band, and turned to the venerable Smith Chart to double check the impedance transformation of the 3 feedline lengths. Its results agreed with the results of the NEC software. I can provide a table of the graph data to anyone who is interested.

It was interesting to see that the 1/4 wavelength feeder gave reasonable impedance levels on some of the bands, and that the 1/8 wavelength case was sometimes better than the 3/8 wavelength case. Impedance levels for a 5/8 wavelength feedline should be similar to those for the 1/8 wavelength case.

I plan to analyze 3 lengths of 450-ohm feedline in the same manner to include in this article. Also planned are studies of 300-ohm and 450-ohm feedline impedance for the loop antenna.

W4BXI - Net control on RV Service Net

Click here for an audio recording of W4BXI on the RV Service Net on 7191 kHz, as heard on my transceiver in Baton Rouge. This was at 0645 CDT this morning. John's signal was reading S9.

Baluns

Here are a few selected articles that were referenced during our recent on-air discussions of baluns, and voltage vs current baluns in particular:

Balanced - Unbalanced - Balanced, by VK5AJL
Lots of good definitions and illustrations.
See the comment posted below by N4NR. Other sources refute the author's contention that current baluns are only designed for 1:1 ratio.

Baluns: What They Do and How They Do It, by W7EL
An illustrated discussion by the author of EZNEC software.

Choosing the Correct Balun, by W8JI
An article that our group has consulted many times.

Broadband Baluns
Focus on air-core and ferrite-bead choke baluns.

Common Mode Chokes
A chart of impedance measurements

Special thanks to W4PRE who directed me to the Chattanooga Amateur Radio Club website that includes many good antenna-related topics on the Links page.

TPWINLOG Data Files

TPWINLOG 2015 creates the following data files to accomplish logging and scoring for the Telephone Pioneer QSO Party:

• BonusCall.txt
• Chapsworked.txt
• CWchapsworked.txt
• LogInFile.txt
• TPHistory.txt
• TPLogOut.txt
• tpqsolog.txt

If you need to edit any of these files independent of TPWINLOG, you must navigate to where they are stored on your system and use a plain text editor, such as Notepad, to make the edits. Be sure to make a backup copy of a file before editing.

The location of these files depends upon how you installed the program. Section 2.1 of the ReadMe file has the following information and suggestion:

THE INSTALL PROGRAM WILL INDICATE THAT IT IS GOING TO
WRITE THE FILES TO: C:\Program Files\TPQ
The install program will create the TPQ folder in the Program
Files folder. OR .. you can click the Change Directory command
button and install to some other folder. Those using Windows
Vista or Windows 7 may wish to change the path to C:\TPQ to
prevent file redirection. This makes finding program written (data)
files much easier.

CASE 1: If you follow this suggestion you will easily find all of the data files in C:\TPQ, as shown in the Windows Explorer screen shot below.

Click to enlarge.

CASE 2: If you allow the program to install to its default directory, the program and data files will reside in two separate directories. The program will be found in C:\Program Files (x86)\TPQ, along with initial copies of two data files that are write-protected, as shown below.

Click to enlarge.

To access the complete set of data files you must navigate to their directory by clicking the Compatibility files button as noted in red above. This will take you to the view that is shown below.

Click to enlarge.

The examples above are from my installations on Windows 7 PCs.

If you must know, the full path to this directory is:
C:\Users\John\AppData\Local\VirtualStore\Program Files (x86)\TPQ
and AppData is a hidden directory, but is easily reached using the Compatibility files button shown previously. Your username will be where "John" appears. You can edit and save the data files in this directory as discussed in the second paragraph above.

If you only need to add some new entries to TPHistory.txt, you can accomplish that from within TPWINLOG.  Enter the station's CallSign, Chapter and Name in the boxes near the bottom of the TPWINLOG window, then click HistoryFileAdd under the HistoryFile menu. Your new entry will be added to the end of the file.

Click to enlarge.

Send me an email or post a comment if you have any questions.

TPWINLOG 2015 -- History File

Based on some questions about how the history file is updated during contact entries in TPWINLOG, I performed some tests this morning.

When the program is installed, the original, default history file (from the downloaded zip file) TPHistory.txt is put into place. While the program is used, the first contact with new station that is not found in the original history file is added to the end of the history file.

We recommend that you practice using the program well in advance of the event, entering practice contacts. Before you start participating in the event you need to delete the log of practice contacts by choosing File, DeleteLog, as shown below.

My testing confirms that this delete function will clear out the following files:
   tpqsolog.txt
   Chapsworked.txt
   CWchapsworked.txt
It will not clear out the TPHistory.txt file. Subsequent use of the program will make use of any new station history data (not in the original history file) that was entered during your earlier use of the program. I tested this by entering a fictitious call sign that I knew was not in the original history file. 

Further testing reveals that changes (e.g. chapter #) made during subsequent contacts with any station will not be saved to the history file. However, TPWINLOG will (apparently) consult the tpqsolog.txt file first when subsequent contacts are made with the station whose details were changed on the previous contact entry. Naturally, those changes will be lost when the practice log file is deleted. Any station details that you wish to preserve need to be entered directly into the history file (using a plain text editor) so that they will be found when you start over with a blank log file. 

Also, if you do make changes to station data during the event, especially chapter changes, you will want to edit your final log file prior to printing results so that you don't end up with something like 2 chapter numbers recorded for the same call sign. 

Please send me email if anything above is not clear or if you have other questions.

Windows Computer Security -- Using a standard user account

By default Windows sets up the initial user account with full admin privileges. This makes it very easy for the user and for malware / spyware / adware publishers to install new programs on your computer. A study reported that of all the security patches issued by Microsoft in 2013, 92% of the vulnerability exploits would have been blocked by use a of standard user account.

Here is the process I have used successfully on 11 Windows 7 computers to convert an existing admin user account to a standard account:

Create a new admin account:

• Log in to your existing user account that has admin privileges
• Go to Control Panel, User Accounts
• Click Manage another account
• Click Create a new account
• Enter a name for the new account (e.g. Admin)
• Click the Administrator button
• Click Create Account
• Click on the new account icon
• Click Create a password
• Enter password (different from normal user password) in the two boxes
• Click the button Create password
• Return to desktop and log out of your normal user account

Downgrade normal user account to standard:

• Log in to your newly created admin account
• Go to Control Panel, User Accounts
• Click Manage another account
• Click on the normal user icon
• Click Change the account type
• Click Standard user
• Click the button Change Account type
• Return to desktop and log out of your admin account

Log in to your normal account and resume use

If you attempt to install a new program or an upgrade (other than Microsoft updates), you will be prompted to enter the password for an admin account. Pay close attention! If this appears for a program you don't recognize or did not choose to install, it may be malware attempting to install.

On rare occasions (in my experience) a program may need to be installed or updated when logged into an admin account. In most, but not all cases, you may be able to simply right-click on the program file and select "Run as administrator". 

Updates 3/27/15: 

• One example of a program that must be run from a logged-in admin account is Evernote. When I am using the program from my standard account and it announces an update available, it tells me to ask my administrator to install the update. It does not make the update available to install by my standard account.
• Many programs allow me to install updates by simply entering my admin password when the UAC pop-up box appears. In some cases the update downloads go to my admin user's download folder rather than to my standard user download folder.

I believe that the same or very similar steps would apply to Windows 8 computers.


Also see these three rules for online security published by Brian Krebs. 

3 Antennas Compared

Recently we discussed the comparative performance of 3 wire antennas, sized for 80 m, on 3.5 MHz and above. I used antenna modeling to compare the following antennas, all at 40 ft above rocky ground:

• W8JI 110 ft dipole
• Horizontal Loop of 287 ft
• 133 ft Off-Center Fed Dipole

I found that the shapes of the radiation patterns vary, but the peak total gain figures are similar among the 3 for the two frequencies I used: 3.5 and 7.2 MHz. Here is a summary of results:

	Maximum Total Gain (dB)
	@ 3.5 MHz	@7.2 MHz
110 ft dipole	5.53	6.59
Horizontal Loop of 287 ft	6.39	5.83
133 ft OCF Dipole	5.74	6.42

Radiation patterns for the 2 frequencies are shown in this PDF file. If you zoom in enough you can read the data on each graph.  Patterns for additional frequencies are easily generated.

I used a similar side-by-side presentation in this 2010 posting when comparing two antennas sized for 160 m (110 ft or 130 ft wire to each side of the feed point).

WA5MLF