Antenna G3SRO

I received an email from Miro OM3CKU with a post he gave us for this portal. I sincerely thank him and am happy to publish:

The aim of this post is not to describe any miracle antenna. I just want to share my experience with the antenna that I built and tested. Previously I used Half sloper z W3DZZ. The main reason for using a half antenna was the size of the land. Full size W3DZZ or G5RV it would fit only in the diagonal of the plot and despite XYZ's great understanding of my "craziness", she was not willing to give consent to erecting a pole in the middle of the plot and thus ruining her view from the window. Another disadvantage is the proximity of the electrified railway line Bratislava - Trnava. The end of the antenna at the border of the property is only 13 m from the nearest track, which caused a large induced voltage, up to 100V, which was able to light the fuse, the other end of which I held in my hand. There was a strong crackle when receiving, which was very unpleasant. That's why I was thinking about some sort of loop antenna, ideally without the need to use an adaptive antenna element.

Antenna according to G3SRO

Voľba padla na anténu G3SRO ktorú som našiel na fotokópii z časopisu RadCom, žiaľ, neviem číslo ani ročník. Elektricky je anténa znázornená na obrázku. Praktická realizácia je veľmi jednoduchá. balun umiestnime na stožiari, prípadne pri jeho päte. Živý vývod spojíme s anténnym vodičom ktorý natiahneme v nám vyhovujúcej výške a vo vyhovujúcom smere. Ak je stožiar vodivý, je vhodné aby balun bol na vrchole stožiara a uzemnený vývod balunu spojíme so stožiarom. Druhý koniec anténneho vodiča upevníme zasa na vyhovujúcom mieste, alebo ho tam iba zalomíme a ťaháme ďalej smerom k zemi. Vo výške cca 1 meter na d zemou upevníme zaťažovací rezistor. Tento má jeden koniec spojený s anténnym vodičom a druhý s uzemnením. V prípade, že aj tento stožiar je vodivý, zemniaci koniec rezistoru spojíme s týmto na vrchole. Zaťažovací rezistor by mal zniesť cca 30 % výkonu ktorý používame. Keďže takýto rezistor v bezindukčnom prevedení ťažko zoženieme, je vhodné ho zložiť z viacerých kusov. Ja som použil 16 kusov rezistorov 1k8/ 2W (MLT 2) tak, že vždy dva sú spojené v sérii, aby vytvorili hodnotu 3k6 a osem takýchto dvojíc je zapojených paralelne. Stredy dvojíc som nakoniec ešte vzájomne pospájal, aby som znížil indukčnosť. Výsledná hodnota takéhoto zapojenia je 450 Ohm, ktorá je vhodná pre výkon TX-u až do 300 W a to napriek tomu, že spočítaný výkon je iba 32 W. Pokusmi bolo totiž zistené, že v bežnej prevádzke CW a SSB znášajú tieto rezistory až trojnásobné preťaženie. V prípade, že preferujete prevádzky pri ktorých je na kľúči položená tehla, napr. RTTY, môžete používať výkon do 150 W bez poškodenia rezistorov.

My implementation of the antenna

My implementation of the antenna is as follows: a balun on a lattice mast 8 m high. To ensure good grounding, this is bridged from top to bottom with RG58 coax in which the middle conductor is connected at both ends with braid. My mast is riveted and had far from good conductivity for vf signals. The antenna wire has a length of 19 m and is anchored to the wall at a height of 2.2 m at the end of the load resistor. Resistor grounding is currently an 8mm diameter 0.5m long pin. I am preparing the grounding using a 1.5 m ground rod, which I will also supplement with horizontal radials buried in the ground, which will certainly improve the PSW. How does such an antenna behave. I measured the PSW using the MFJ 269. In the range of 1.7 to 35 MHz, the PSW did not exceed the value of 2, with the exception of 26.3 to 27.2 MHz, where the PSW was up to 2.5. In the amateur bands, the values ​​were around 1.4 to 1.7. The suppression of industrial interference from electric traction proved to be very good. While he was pointing at the original antenna S-meter S 6 to 7, after connecting the G3SRO antenna, the interference dropped to S 3, which represents at least 18 dB, or 1/8 of the original.

Conclusion

Don't expect miracles from this antenna, they don't even happen at Christmas these days. "Gain" is approximately equal to the slanted beam, or as we are used to say in amateur practice Half sloper. However, it has a huge advantage in that it does not need an adjusting member and at the same time it is less susceptible to static electricity. This makes it particularly suitable for "field" conditions and where we cannot install a full-size antenna. If you cannot ground either end, it is possible to use a counterweight, or connect the grounded ends with any wire. Such a solution is also suitable if there is a risk of a potential difference at the installation site due to high ground resistance (rocky or dry soil). I wish everyone who gets inspired much success.

Miro OM3CKU