#antennas — Public Fediverse posts

TechTip #3 Improving the “Titanic” 40m field expedient backpack portable antenna

TechTips on Ham Radio Outside the Box are brief posts of a technical nature.

Back in October 2024 Ham Radio Outside the Box introduced an interesting design for a compact, field portable antenna for the 40m band. Named the “Titanic”, it was a T-antenna similar in appearance to the one used on the tragically famous ship that sank in the Atlantic Ocean in 1912 during its maiden voyage. I recommend reading the original post to get the background information.

Recently I was wondering whether there is some way to improve the design by eliminating the loading coil without sacrificing the portability of the “Titanic”. It is a very simple design in which a shortened vertical element is top-loaded with two sloping wires acting as a capacitance hat. The vertical element can be supported on a short telescopic fiberglass pole.

There are two possibilities to consider: increase the length of the vertical element or, increase the length of the top hat wires. Or maybe both. After some experimenting I chose both options. Here are the design changes I implemented.

The revised “Titanic” antenna’s sloping top hat wires are supported on trekking poles, although raising the ends higher does improve the SWR. In order to preserve the rapid deployment feature of this field antenna the trekking pole support option, at about 4 feet, worked sufficiently well for me. The SWR seen by the radio at the far end of 25 feet of RG-58U coax is around 1.2:1.

Note the very compact size of this antenna. It is a stealthy option when operating in busy locations like public parks. It uses far less space than a 40m dipole and, if the dipole is erected as an inverted-V, it will exhibit the same omnidirectional radiation pattern, but perhaps with a lower take-off angle.

The “Titanic” should be considered an experimental antenna since I have not subjected it to field testing in a live-fire RF exercise yet, but it is a promising design that others have spoken well of (references available in the original post here on Ham Radio Outside the Box). If you try this antenna please let me know what kind of results you get.

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Поставил свой личный рекорд - две навайбкоденных тулы для себя за день.

Предыстория: я в какой-то момент решил, что хочу побаловаться не только с LoRa антеннами, но и с LTE для дачи, продал свой NanoVNA-H4 и взял себе NanoVNA-F V3, который работает до 6 GHz.
Но в какой-то момент обнаружил, что в него нельзя вставить флешку и он не делает скриншоты фреймбуфера как это делал более простой и старый вариант.

Впрочем, это меня не остановило и я быстренько с Codex нафигачил две штуки:

• vnacg - генератор графиков в стиле NanoVNA по S1P/S2P входному файлу (их пишет NanoVNA), только в большом разрешении, без ограничения по маркерам и ещё пачкой других фишечек, которые делают демонстрацию замера именно в качестве графика ещё удобнее.
• vna-android - крайне примитивная, но полезная в поле штука, которая запускается на телефоне и по USB забирает фреймбуфер с NanoVNA, грубо говоря делая скриншоты извне.

Обе тулы работают только с NanoVNA-F V3, но если вдруг будет нужно, то добавить поддержку других моделей не должно быть большой проблемой.

Теперь я могу и прямо в поле пошарить скриншот, и сгенерить красивый детальный графичек уже дома.

#dev #agents #vibecoded #log #generated #Go #Kotlin #tools #NanoVNA #radio #DIY #automatization #Codex #pic #antennas #LTE