How I found the best antenna for my SOTA/POTA activations

by Thomas (DM1TBE)

Intro

Until January this year I had a German “Klasse E” / CEPT-novice amateur radio license (equivalent to the US General Class), which limits the use of HF to the 10-,15-, 80- and 160-meter bands. When I started with SOTA I used homemade single band end-fed antennas most of the time. However, that is only feasible for the 10- and 15-meter bands.

Unfortunately, both bands are very moody and sometimes they have not worked at all. Unlike the UK for example, FM is uncommon for SOTA in my home association DM (i.e. Germany Low Mountains). You can be lucky and get your 4 QSOs, but I did not want to rely on pure luck.

Therefore, I bought an end-fed half-wave antenna for 10-, 15-, 20-, 40- and 80-meter bands, after some experiments with 10-80-meter end-fed half-wave antennas, from a small German company called ANjo.

Although I could not use the 20- and 40- meter bands at that time, the EFW80-10P (en: auto-translated) antenna gave me the possibility to use the 80-meter band. The antenna could also be tuned for 15. It has a mechanical length of 23.6 m / 77 ft and a coil for the 80-meter band. It is pretty lightweight with 0.4 kg / 14 oz and allows up to 30 watts PEP – more than enough for me. 80-meters is not the best band for daytime SOTA activations, but in 21 months doing SOTA activations, it worked 37 times and tipped the scales for an activation from time to time.

It was sometimes a bit tricky to raise the long wire into the air, but it always worked … better or worse …somehow … like here in the woods along a trail.

In January this year, I upgraded my license and a new world of HF-bands opened for me. Although I have learned a lot about propagation for the exam, I am in favour of a German saying: “The difference between theory and praxis is larger in the praxis than in the theory”.

So I wanted to know which bands work best for me at portable operations. My requirements were:

1. Coverage of short to medium distances
2. Antenna as small/short as possible
3. WARC would be a plus as I have often seen a friend struggle a lot with crocodile stations taking his frequency, especially during contests
4. All of the above during daytime

As you can see in the following map, the vast majority of hunters are within a 1600 km / 1000 mi radius around me. Extending the reachable distance would not help me a lot, as the ham radio operator density in Africa is low, and the Russians don’t fancy for SOTA – I don’t know why. If you do, please let me know in the comments.

The Test

For the test, I have used a WSPR transmitter from ZachTek. Unlike the transmitter from Sotabeams, it has GPS built in for exact time and the locator.

You can test several bands at once, as the transmitter loops over the selected bands.

So I selected the 10-, 12-, 15-, 17-, 20-, 30-, 40- and 80-meter bands and let in run for several days. For the analyses and the charts, I have used the website WSPR Rocks! which provides a wide range of different WSPR evaluations as a table, chart, map or statistic. I have chosen “distance vs time of the day”.

The Results

Some of the results were pretty much as expected. For example, the 80-meter band provided a reliable coverage over all distances – but only during the night. The 10- to 15-meter bands were quite good for DX during daytime but left a hole at short and medium distances. The 20-meter band did not work well on short distances, and is often very populated, especially during contests.

Overview, x-axis time, y-axis distance:

Only the 30- and 40-meter bands provided a pattern as I have hoped for. Both worked good during the daytime on short and medium distances. At the end, my favourite was the 30-meter band. As a WARC-band it is not available for contests, provides exactly the coverage as I wanted, and allows for smaller antennas than the 40-meter band.

30-meter band:

I am aware that the results differ with the antenna used, the environment and how you erect the antenna (i.e. takeoff angle), but it gave me a comparison between the bands and daytimes, and provided results that I can realistically archive. You can see all charts at the end of this post.

Luckily, the company that made my 10-80 end-fed half-wave antenna provides a wire drop-in replacement for 15/30-meter bands.

It has a mechanical length of 8.2m / 27ft and a coil for the 30-meter band. I usually pull the antenna up on a 10m / 33ft fibreglass mast.

If the environment does not allow a pole for any reason, I use the 30-meter band with the PAC-12.

So far, I have made six SOTA/POTA/WWFF activations since my license upgrade in January 2023 on the 30-meter band. The 167 QSOs during activations in total are right there where I wanted them to be – some QSOs are not displayed in the map below due to missing locators.

So, I am happy with my choice so far. Maybe I will focus more on DX during my activations when it’s become warmer and the time allows. The mentioned company also offers a 12/17-meter drop-in replacement. I will let you know ?

Appendix

10m

12m

15m

17m

20m

30-meter -see above

40m

80m