G3SRO antenna
I received an e-mail with a contribution from Mira OM3CKU, which he supplied to us for this portal. Thank you very much and I am happy to publish:
The purpose of this post is not to describe any miraculous antenna. I just want to share my experience with the antenna I built and tested. I used to use Half sloper from W3DZZ. The main reason for using the half antenna was the area of the land. The full-size W3DZZ or G5RV would only fit in the diagonal of the plot and, despite XYZ's great understanding for my "scolding", was not willing to give its consent to the position of the mast in the middle of the plot and thus destroy its view from the window. Another disadvantage is the proximity of the electrified railway line Bratislava - Trnava. The end of the antenna at the boundary of the plot is only 13 m from the nearest track, which caused a large induced voltage, up to 100V, which managed to light up the incense which other end I held in my hand. A strong crack appeared on reception, which was very unpleasant. That's why I was thinking about some loop antenna, ideally without the need to use an adapting antenna member. The choice fell on the G3SRO antenna, which I found in 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 place on a pole, possibly at his heel. We will connect the live terminal with the antenna conductor, which we will stretch in a height suitable for us and in a suitable direction.. If the mast is conductive, it is suitable that the balun is at the top of the mast and we connect the grounded outlet of the balun with the mast. Fasten the other end of the antenna wire in a suitable place, or we just wrap it there and pull it further towards the ground. At a height of approx 1 meter on the ground we attach a load resistor. This has one end connected to the antenna wire and the other to ground. In case, that even this mast is conductive, Connect the ground end of the resistor to this at the top. The load resistor should withstand approx 30 % the power we use. Since such a resistor in a non-inductive design is difficult to obtain, it is advisable to assemble it from several pieces. I used to 16 kusov rezistorov 1k8 / 2W (MLT 2) so, that always two are connected in series, to create a value of 3k6 and eight such pairs are connected in parallel. In the end, I still connected the middle of the pairs, to reduce inductance. The resulting value of such a connection is 450 Ohm, which is suitable for TX power up to 300 W and yet, that the calculated power is only 32 W. Experiments have revealed this, that in normal operation CW and SSB these resistors withstand up to three times the overload. In case, that you prefer operations in which a brick is placed on the key, e.g.. RTTY, you can use power up to 150 W without damaging the resistors.
My antenna implementation is like this: balun on a high lattice mast 8 m. This is to ensure good grounding bridged from top to bottom by coax RG58 in which the middle conductor is connected at both ends with a braid. My mast is riveted and had far from good conductivity for RF signals. The antenna wire has a length 19 m and at the end of the load resistor is anchored to the wall at a height 2,2 m. The resistor ground is currently a pin with a diameter 8 mm and length 0,5 m. I'm preparing the ground using a ground rod 1,5 m, which I will supplement with horizontal radials buried in the ground, which will definitely improve the PSW. How does such an antenna behave. I measured PSW using MFJ 269. Ranging 1,7 to 35 MHz did not exceed the PSW value 2 except 26,3 to 27,2 MHz where was PSW 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 pointing to the original antenna S-meter S 6 to 7, after connecting the G3SRO antenna, the interference dropped to S 3, which is minimal 18 dB, or 1/8 original.
Conclusion. Don't expect miracles from this antenna, they don't even happen today at Christmas. "Gain" equals an approximately oblique beam, or as we are used to talking in the amateur practice of Half Sloper. However, it has a huge advantage in this, that it does not need an adapter and at the same time 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 can't ground any end, it is possible to use a counterweight, or connect the grounded ends to any conductor. Such a solution is also suitable in the case of, that there is a risk of a potential difference at the installation site due to high earth resistance (stony or dry soil). I wish everyone who is inspired by a lot of success.
Miro OM3CKU