Sunday, February 14, 2016

160 m Horizontal Loop Analysis

Here are some plots generated from the NEC analysis of a square horizontal loop at 45 ft above fertile ground, consisting of 540 ft of 12-gauge copper wire.

Below are 3-D radiation patterns for selected frequencies. 2-D plots in the horizontal plane or vertical plane can also be produced for any azimuth or elevation angle. These are based on the source (transmitter) being connected at the midpoint of one side of the square loop. The default NEC modeling of a feedline assumes no radiation, so the patterns are unaffected if a feedline is included.
Click on any graphic for a magnified view.

1.8 MHz
3.6 MHz

5.357 MHz

7.2 MHz

10.1 MHz
14.2 MHz

18.1 MHz
21.2 MHz

24.9 MHz
28.5 MHz

Below are plots of SWR and feed point impedance (magnitude in ohms) for 3 different lengths of the loop:  528, 540 and 552 ft. The legend at upper right identifies each case by color of the plotted data curves. Each curve is based on 188 data points. Click on any image for a magnified view.

SWR vs frequency

Impedance at feed point

I've also analyzed the effects on SWR and impedance of including a feedline length with various lengths, but need to validate the results further before posting here. Previous analysis and measurements of an actual 80 m loop indicated that the SWR dips shifted toward higher frequencies as the feedline was shortened.

Friday, December 11, 2015

HF Radio Propagation Modeling

Today's antenna modeling programs, like EZNEC and 4nec2, use the decades-old NEC program code to calculate the electric and magnetic fields produced by an antenna in 3 dimensions. (They also model parameters like impedance to assess the power efficiency of the antenna and transmission line combination.) We normally look at the radiation pattern results for the far field, considered to be greater than 2 wavelengths away from the antenna. NEC-based software is not equipped to model the fields at a great distance. The software does not model what happens to the electromagnetic energy as it propagates over a long distance.

To complete the picture of radio communication between two HF transceivers we need to look at radio propagation tools. Here are two links that list some of the available resources:
Both links make reference to VOACAP, which I became aware of while using 4nec2. I have not yet tried to use it, but I saw that VOACAP has both online and downloadable versions. 4nec2 has a utility for exporting an antenna design in the format required by VOACAP to model the propagation. Common pre-built antenna models can also be used as inputs to VOACAP. For point-to-point propagation modeling the design of the antenna at each end should be known. The first link above has a nice primer on VOACAP and a quick guide with lots of information.

The second link above also lists a program HFWIN32 which is said to contain 32-bit versions of three published propagation modeling tools: ICEPAC, VOACAP and REC533. Some more recent instructions and links are available at this web site.

A newer, freeware program HamCAP is designed to interface with VOACAP to predict HF radio propagation.

Playing with these propagation models may contribute to a better understanding of which antenna types should work best for a given frequency, time of day, geographic locations and solar conditions.

Friday, November 20, 2015

The History of Southern Regional Center (SO) and the WEDIXIE ARC

by G. Warren Coleman / WD4NIT

The WEDIXIE Amateur Radio Club began in 1968 at the Western Electric Southern Regional Engineering Center in Atlanta, GA. WEDIXIE was a prefix that applied to all of the corporately-sponsored employee clubs at the site, including an active scuba club, a personal computer club, an indoor and outdoor recreation club, and of course, the ham radio club. The WE in WEDIXIE stands for the Western Electric Company. The DIXIE portion of the name of course refers to the location's southern heritage.

Western management provided the club with a room in the facility to serve as a ham shack. It was located on the first floor and was about 12-15 ft square. The antennas were located on the roof, and included both wire and beam antennas fed with runs of coax and 7/8 inch Andrews Heliax cable.
In 1984 the American Telephone & Telegraph Company (AT&T), the original owner of Western Electric, changed the WE-CO name to AT&T Network Systems. In 1996, AT&T spun off the company, which then became Lucent Technologies. Around 2002, a greatly downsized Southern Regional Center moved from 6701 Roswell Rd in Sandy Springs, GA, to Alpharetta, about 15 miles to the north. The original property was sold and most of it was eventually demolished. In 2006, Lucent was purchased by and merged into the French-based company Alcatel, which changed its name to Alcatel-Lucent.

By the time the Regional Center was moved to Alpharetta, only two active employees of the radio club remained and the company decided they would not sponsor a club there. Not wanting to let their beloved club call WB4MZO be reassigned elsewhere, the club's retired members reincarnated the WEDIXIE ARC as a retiree club and received permission from Lucent management to continue to use the WE trademark in its name. We still fondly remember the "Good Old Days," and strive to keep the club active and to preserve the Western Electric Company spirit.
Our members, though still active amateurs, now move a little slower than they once did, but we remain ready and able to assist the community in times of need. We have elected club officers and a trustee, and our club members especially look forward to participating in the annual Field Day exercise each year, a contest which has had a WB4MZO presence since well before the turn of the millennium.

Friday, October 30, 2015

Google Hangout Setup for Radio Patch

This document presents the steps for setting up a Google Hangout for voice patching to a transceiver or other applications. It assumes that you have already established the required transmit and receive audio interfaces between a transceiver and a computer that runs the Google Hangout Internet application. It is convenient for the control operator of the transceiver to join the Hangout with a separate computer, tablet or smart phone for the purpose of monitoring the patch audio and speaking to other participants on the Hangout.
Updated 11/02/2015

Sunday, October 18, 2015

TPWINLOG File Locations

If you are using Windows 7 or Windows 10, and:
  • if you directed the TPWINLOG 2015 program to install in C:\TPQ then all the files you need (including TPLogOut.txt if you print to file) will be located in that folder.
  • if you allowed TPWINLOG 2015 to install in the default folder:
    C:\Program Files (x86)\TPQ
    then your files (including TPLogOut.txt if you print to file) will be located at:
    C:\Users\name\AppData\Local\VirtualStore\Program Files (x86)\TPQ
    where 'name' is the Windows user name under which the program was run.
In Windows 7, if you navigate to the program's folder C:\Program Files (x86)\TPQ
you can reach the data folder by clicking on Compatibility files, as shown in the screen shot below.

click above to enlarge
The Compatibility files button shown above for Windows 7 does not appear to be available in Windows 10, but you can open the file explorer at C:\Users and 'drill down' to 
C:\Users\name\AppData\Local\VirtualStore\Program Files (x86)\TPQ
where 'name' is the Windows user name under which the program was run.

Another option is to search for tpqsolog using the search box near the upper right corner of the file explorer in either version of Windows. However, since AppData is a hidden folder, you may need to start your search there, rather than at a higher level in the folder (directory) tree. I found that a standard (non-admin) user search starting at C:\Users would not find the file tpqsolog.txt, but the same search starting from C:\Users\name\AppData does find the file.

Tuesday, September 15, 2015

Map of Members on Saturday Net

Here are two views from Google Earth that show the locations of Bell Ringer members who have checked into our Saturday morning net during the past two years, according to records kept by W4BXI. The first view covers a wide area to show all station locations. Four circles show a range in miles from W4BXI's location. The legend at top right gives the radius for each circle.

Click on map for enlarged view.

The second view covers a smaller area to expand the view of the many stations located in Alabama and Georgia. Three circles show the range in miles from W4BXI's location.

Click on map for enlarged view.

These map views may help us to better understand the variation in reception among our members according to their ranges and the radio propagation experienced by frequency band and time of day.

I can easily add and remove stations and generate range circles centered on any point on the map.

Sunday, May 31, 2015

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:

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.