The Great Antenna Story

Written by Irvin H. McKee Jr., Rockford, Illinois, United States of America
July 2005






 

After running my MACO M105c for five years, I felt it was time to go better.

I wanted an antenna that would be interference free for my neighbors, allow me to reach further around the world, and take advantage of the DX as it rolled across the skies.

The MACO M105c was a 25-foot boom, five elements, with a quad type reflector place on top of a 72-foot Rohn 25 tower. With the assistance of Mother Nature, the DX would allow me to talk to Mexico, Australia, Canada, Jamaica, and across the United States.

I decided I wanted to use an 8-element antenna. Using reference materials I have collect over the 30 years I’ve been in this hobby I mapped out an element pattern for a 42-foot boom. Being confident that this antenna would meet my needs I built it in the back yard last fall. Now it was a matter of waiting for spring to have it lifted onto the tower.

Having a few months of down time on this project I started looking on the internet to see what might be out there. It wasn’t until the beginning of May 2005 that I came across Paolo’s website, http://diana.bib.uniurb.it/arrl/yagi.htm. I became excited by the graphs he showed on this site. The patterns on his Yagi antenna were so tight front to back that it made me wonder what the pattern would look like with the 8-element antenna I had sitting in my back yard.

His website gave an email address and I wrote him asking what his thoughts were regarding the design I had. He ran the pattern using a software program Eznec. We were both disappointed by the results.

Many emails followed and with his help I have what I prefer to call THE SUPER TIGHT 7.


The Super Tight 7 uses a 42-foot 3-inch diameter boom on top of a 62-foot Rohn 25 tower. The elements are 72 inch 5/8 inch tubing on all elements for the director and driver they are inch diameter and will vary with the element length. The reflector uses inch diameter tubing for 66 inches and 3/8-inch diameter tubing which again varies with the reflector length. The spacing is right side.

Added by Paolo: diagrams for gain, F/B, SWR,


spacing
dia. 5/8". dia. 1/2"
dia. 3/8"
reflector at 00.0" 36" 66" 8.10"
driver at 43.0" 36" 70.0"
director at 64.6"
36" 67.55"
director
at 139.5"
36" 63.38"

director
at 260.0"
36" 62.46"

director at 373.5"
36" 62.07"
director at 500.0"
36" 54.13"


The antenna is now in place, and in operation.

The antenna is working great. The SWR is 1.13 at 27.4 MHz on both polarities. I used a MFJ brand SWR analyzer, the antenna tested at 2.1 at 26.6 MHz and again at 2.1 at 27.99 MHz.

In the past when talking with a person 50 miles away I would get a signal report of 3 to 4 "S" units, with the ST7 my signal reports are coming back at 6 to 8 "S" units. An increase of up to 4 "S" units. Looking back on the charts Paolo provided by email my SWR’s are very close.

I was concerned about the supports reflecting. If you look at the photos, you’ll see that I isolated them. They don’t seem to be effecting my signal at all.  This antenna is a great improvement over the 25 foot 5 element I was using. I couldn’t be happier with the results.

And on a more personal note. My brother Steve lives in the state of Tennessee, 600 miles away. If the conditions were right we might be able to catch each other maybe 2 or 3 times a year. In the first 3 days of running with this antenna Steve and I have talked twice. We look forward to many evening of sharing stories over the airwaves.

Many thanks to Paolo, without his help this project would not have been so successful. Thanks Paolo!