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

The choice fell on the G3SRO antenna, which I found on a photocopy from RadCom magazine, unfortunately, I don't know the number or year. Electrically, the antenna is shown in the figure. The practical implementation is very simple. balun we place it on the mast, or at its foot. We connect the live outlet with the antenna wire, which we stretch at a suitable height and in a suitable direction. If the mast is conductive, it is advisable for the balun to be at the top of the mast and connect the grounded outlet of the balun to the mast. We fix the other end of the antenna wire in a suitable place, or we just bend it there and pull it further towards the ground. At a height of about 1 meter on the ground, we fix the load resistor. This has one end connected to the antenna wire and the other to ground. If this pole is also conductive, we connect the grounding end of the resistor to this one at the top. The load resistor should withstand about 30% of the power we use. Since it is difficult to find such a resistor in a non-inductive version, it is advisable to assemble it from several pieces. I used 16 pieces of 1k8/ 2W resistors (MLT 2) so that each time two are connected in series to make a value of 3k6 and eight such pairs are connected in parallel. In the end, I connected the centers of the pairs to each other to reduce the inductance. The resulting value of such a connection is 450 Ohm, which is suitable for a TX power of up to 300 W, despite the fact that the calculated power is only 32 W. It was found through experiments that in normal CW and SSB operation, these resistors can withstand up to three times the overload. If you prefer operations where a brick is placed on the key, e.g. RTTY, you can use power up to 150 W without damaging the resistors.

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