Field Day 2021

Posted by Fred C (W6BSD) on Jul 01 2021

Field Day 80/40-meter antenna

The 2021 Field Day was the first time member of the San Mateo Radio Club met in person since the pandemic. It was nice to see friends again after so long, but the most enjoyable part was to be in a group of people working toward the same goal.

Smith Chart dipole on 80/75-meter
Smith Chart dipole on 80/75-meter

A few months before this event, I designed a multi-band antenna to work the entire 80/75-meter and 40-meter. You can read more on the design of that antenna in my previous post. Field Day was, for me, the opportunity to see how that antenna was working.

SWR on 40-meter
SWW on 40-meter

The antenna has been installed between 2 tall trees 400 feet apart. There were more than 150 pounds of tension on the 80/75 meter branch of the antenna. Despite that amount of force and the long distance between the two trees, the antenna was still sagging. In the end, the feed point was at 50/55 feet in the air. It was too low, and the dipole on the 80-meter band was acting mostly as an NVIS1.

SWR on 80/75-meter
SWR on 80/75-meter

The 40-meter branch was set up as an inverted Vee. It behaved like a conventional dipole at the height of 55 feet with a take-off angle between thirty and forty degrees.

The three graphs on the right side show the Smith Shart and SWR after installation of the antenna. As you can see, the antenna has a low SWR almost all the 80-meter band. It allowed the operators to work CW and Phone without using an external tuner. The internal tuner of our rigs could easily fine tune the antennas and present a 1:1 SWR.

The following pie chart shows 20% of the QSOs are were made 80-meter. You cannot see that on these graphs, but half were using CW, and the other half were on Phone. This year, we didn't use digital on the 80-meter band. As the graph on the right side shows, most contacts were on the west coast, CA, OR, and WA. It confirms the antenna, at that hight, is NVIS1.

Contacts on 80M and bands worked
Contacts on 80M and bands worked

The antenna has been working exceptionally well across the entire 80-meter band. The problem we need to solve for next year is the height. To increase the number of contacts on the east coast, we need a lower take-off angle. By putting the antenna in a different part of the park, we could use two eucalyptus 20 to 30 feet taller. It is not much, but anything will probably help.

Pictures


80-meter antenna during installation
80-meter antenna during installation

San Mateo Radio Club field day setup
San Mateo Radio Club field day setup

  1. Near vertical incidence skywave 


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