Linked Dipole

Multiband Dipole for 80/60/40/30/20m – matching the (tr)uSDX Low Bands configuration

I used https://www.sotamaps.org/extras as baseline, but deviated quite a bit from it.

First of all, I added a 1:1 Balun to prevent common mode currents. As we all know: A Dipole is a symmetrical Antenna, while coax cable is asymmetrical, so we need a BalUn (which stands for “Balanced / Unbalanced”)

This was done by winding a coax Balun on a FT140-43 core according W1JR Scheme:

The BalUns Attentuation on the outside (coax-shield) was confirmed by measurement

37-40dB of Attenuation on the desired Bands is more than enough

A 3D-printable housing was designed, so it would not waste any space and had a cover that would close tightly without need for screws:

2mm connectors as inlets, so it´s waterproof.
The lid snaps in the housing and is tight !

Labelled “link insulators” for ease of use

Then it was time to figure out the wire lengths.

Source: https://www.sotamaps.org/extras

I was planning to use it with my 7m pole (10m “Mini” pole without top 4 segments) and 3m rope extension, so the ends do not need support poles and are off the ground. This is important, as the height of the ends above ground extremely influences the behavior of the Antenna. Watch the Video (on Top of the page) where I show 80m Band measurement at nominal height and with pole lowered !!!!

Long story short: The suggested lengths did not work, and after carefully measuring and shortening all the elements in the field, I came up with the following working lengths:

This pic shows why we need the additional lengths for creating the loops at the links (10cm on each side of wire/15cm at feeding point)

Here are the measurement results:

Here are all the printables for this project, so you can build one for yourself:

3D Printable HASP. You can scale it up or down, to fit your personal needs. I´ve scaled it to 120mm width for the linked dipole. Credits to oxyge65 for designing and sharing.