Build a 20m Dipole

Why a 20m dipole?

A squirrel chewed through my 40m EFHW and it was nearly right in half, so I trimmed one end, extended the other, and turned it into a 40m dipole.

Problem was that I forgot that a 1/2 wave dipole doesn’t resonate well on the higher harmonics, and I work 20m way more often than 40m. So I cut down the wire again and made myself a 20m dipole instead.

Incidentally, this is when I realized that there is a lot more to love about an EFHW than “Convenience of installation”.

Construction

Building this antenna couldn’t be simpler. I cut the end of a cheap patch cord, stripped the coax, and soldered 5m of wire to each of the inner conductor and the outter braid.

Sealed up with some heat-shrink

The completed antenna.

Installation

The feedpoint sits atop my pergola; you can just see the connector peeking over the top.

I attached insulators to both ends.

One end went up into the tree, with the twine secured near ground level, and the other was raised up with a roof-rake pole.

Testing

I put the nanoVNA onto it and at first things did not look good; the antenna seemed far longer than it should. I realized that I should probably install a choke at the feedpoint, otherwise the coax braid would be part of one of the radiating elements. This ended up looking a bit short, but it was good enough that I didn’t bother with any additional tuning.

Very low SWR around the SSTV range, and still very usable near the bottom of the band with the tuner built in to my rig.

The FT8 test was reasonable looking.

I’m definitely getting out, but signal reports were all very weak, after all my antenna is barely 12ft off the ground at the highest point! Propagation has been a bit soft lately anyways, I heard it’s D-layer absorbtion season. All those factors aside, I still made an 8900km QSO w/ RK9UN, but maybe that just proves that FT8 is magic.