My HF-project has stalled since I do not have a decent antenna. I have limited space for a full-sized antenna on my roof. My friend LA8OKA has assembled a loaded 20m dipole, and I wanted to test a similar design so I could get on the air on 20m.
First I simulated the antenna in EZNEC+ 6.0. The antenna is about 6m with 9uH loading coils halfway on each dipole segment.
Above, the parameters in EZNEC. I created two coils at about 9uH, which I calculated as 0R+791j ohm.
This is how the antenna looks like in EZNEC.
The SWR minimum is 1.34 at 14.05 MHz, meaning that the antenna should be great for WSJT work at 14.0760 MHz.
Then I created the two coils using 32mm PVC and 23 turns of 1mm2 multicore copper wire. I calculated the inductance to be 8.8uH, and a prototype coil proved to be in the ballpark of the calculated value.
Picture of the coil (in the rain).
I used a cheap 1:1 China-Balun as the center isolator.
Then, I mounted the antenna on a test location on my balcony and tuned the antenna using a NWT150 scalar network analyser and a directional coupler.