| January 12, 2026 19:57 UTC | 3 | Progress update... | #hamchallenge week 3: Understand how your antenna works. ๐งต
Let's check out the lowband vertical antenna I built before #CQWW in November. It is 16.5m long, built with an 18m Spiderbeam mast minus the top element. About 18m of wire are coiled up on it (for stability), and it is tuned at the feed point with a CG3000 automatic tuner. There are 12 ground radials with an average length of 10m below it. When I built it and laid out the radials, I noticed that the feed point impedance stayed at about 37 Ohm at the resonant frequency of ~ 4.1 MHz any more after 12 radials, so I left it like that. HC03 @hamchallenge #hamradio #antennas
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| January 12, 2026 20:09 UTC | 3 | Progress update... | @hamchallenge HC03 - To gain some insights by simulation, I modeled this very simple antenna in MMANA-GAL. In order to achieve the same resonance frequency as I measured, I had to make the antenna a little longer, about 17m. On 80m, the main band of operation, simulated resonance is at about (20.5 - j166) Ohms at 3.5 MHz and (25.5 - j100) Ohms at the upper band edge. That is quite a difference in radiation resistance we see here! Considering ground losses, every Ohm gained in the real part is a win. Also, adding just 1m of wire to the top of the antenna adds about 4 Ohms to the real part. So I really should reconsider if it was a good idea to leave the top element of the mast out... On 160m the impedance is only about 4.5 Ohms. Therefore, a lot of losses can be expected by my less-than-perfect ground and losses in the tuner.
The simulation results for 160m - 30m are plotted below but the reality will be worse on the lower bands because ground losses are not included here.
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| January 12, 2026 20:19 UTC | 3 | Success! | @hamchallenge So, what is next? I think I will optimize this antenna for 80m by adding the missing last element to it, add some more radials, and build a tuning box that can handle more power than the CG3000 automatic tuner, so I can operate with high power. For 160m I will build an T-antenna in the trees behind the barn. It may have a shorter vertical part, but the top capacity will make up for it. HC03S |
| January 12, 2026 20:16 UTC | 3 | Progress update... | @hamchallenge What are the real-world results of this antenna? As expected, on 80m I feel pretty loud with this antenna and "only" 100W. Tonight I spent quite some time on 80m CW. Over the course of two hours I was copied five times by JN1ILK's CW Skimmer. Not loud, but despite quite a lot of CW activity on 80m in Europe, only a handful of those stations made it to Japan at all!
I didn't spend much time on 160m yet with this antenna but it was good enough to work K1LZ in the Stew Perry contest. The real test will come during CQ 160m CW in two weeks, but judging by the figures (low radiation resistance) I can already say that this antenna won't be a great performer for DX. HC03
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| January 12, 2026 20:32 UTC | 5 | Progress update... | #hamchallenge HC05 - Use HAMNET!
This is something I should have done a long time ago already - especially since I have line of sight to the Olympiaturm in Munich, which hosts DB0TVM (picture shows the view from my flat). However, according to hamnetdb.net it is currently under renovation... https://hamnetdb.net/index.cgi?q=db0tvm - I will observe the status. Would be much nicer to access the hamnet via radio rather than some VPN... #hamradio #hamnet @hamchallenge |