twa.ninja | Tim's Site for Stuff

20m Dipole

I just made a very simple 20m dipole. It's two lengths of wire connected to an SO-239 connector in a PVC enclosure, and tied off to the swamp cooler on top of my roof and a nearby tree. I cut each wire to 18'-0" long initially, and folded it back ~9 inches to ~17'-3" of wire on each leg. After testing, I folded it back and wrapped it around at the ends to ~16'-7". In testing it, I get an SWR of ~1.67 to ~1.77 over the 20m ham band, so good enough for me. I was curious to see if removing the folded back wire would cause any issues, and it caused my center frequency to go up to ~14.6MHz, resulting in a measured SWR of ~1.75-2.0 in the 20m band. I soldered the extra length back on and left it wrapped on there to get the tuned chart you see below. I am able to hear lots of traffic using my new uBitX, as well as my LimeSDR Mini. See below for photos of the swr testing and waterfall on the LimeSDR. I definitely need to get an fm filter for the LimeSDR, as it picks up a ton of FM harmonics in the 20m band. Luckily iirc the uBitX has a filter to block everything above 30MHz, so I shouldn't have this issue on there.

Image: 2018-05/swr-for-dipole-first-attempt.png

SWR Without Tuning

Image: 2018-05/swr-for-dipole-tuned.png

All HF - Tuned

Image: 2018-05/swr-for-dipole-tuned-20m.png

20m Band - Tuned

Image: 2018-05/20m-waterfall-pre-fm-filter.png

FM Harmonics Waterfall

Permalink - Tags: hf, ubitx, antenna - Categories: Electronics, Radio
Written by Tim on 2018-05-28 20:53 UTC