Made from bits from the scrap yard and a cheap plastic box.
This project gives me a nice excuse to buy an antenna tuner!
The two active elements are made from copper pipe. Cut to be 4'6" for resonance at 52MHz, which is the middle of the 6 meter band. The two halves will be mounted in a vertical polarization, due to the radiation pattern of this type of antenna.
I got the proper connectors to connect the antenna to my NanoVNA netwrok analyzer so I could start tuning the antenna. My plan it to tune it to 52MHz and hope that the copper pipe gives me enough bandwidth to keep under 1:1.5 SWR across the entire 6M band: 50-54MHz. I left the pipes long so I could trim them down until I get to the right length.
Before tuning, this is what my NanyVNA is reporting:
As you can see, that 0.50in changed the resonant frequency to about 42.5MHz or 1.5MHz per 0.50in. My -15dB signal loss bandwidth has stayed within desired parameters as well!
Next I cut off an entire inch from each pipe, expecting the new resonant frequency to be about 46Mhz and lo:
My prediction was not correct! I continued to make cuts in this fashion until I hit the sweet spot at 52MHz. In making these cuts, I found that having the slightest variance in length between the pipes made a big different in the reflected power. 1/8" longer on one pipe changed my VSWR from 1.09 to 1.22!
In the end I decided to settle after the following readings:
I had to cut the antenna a bit shorter than I had initially expects, and I think this is due to the length of the wires from the inside of the box, from the jack to the pipes.
I also noticed that the readings on my NanoVNA varied depending on the the position I was holding the antenna. I will do more analysis once I have it mounted, but I believe this is close enough to put on the roof tomorrow!