NOISE ADVANTAGE OF LONG WIRE ANTENNA FAR END TERMINATION

Useful information regarding antennas for SDR products.
glovisol
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Re: NOISE ADVANTAGE OF LONG WIRE ANTENNA FAR END TERMINATION

Post by glovisol » Mon May 27, 2019 3:48 pm

THE MODIFIED BEVERAGE ANTENNA PLANT - 1

As previously mentioned, the modified antenna has a 450 Ohm termination and a 3.6 m deep ground stake at the far end. At the receiver's end the antenna is terminated by the primary of a low noise/low capacitance 450 to 1000 Ohm transformer. The secondary is kept floating and is connected to the P and N input terminals of the RSPduo, as shown in the schematic below.

The return of the isolation transformer primary is connected to the counterweight. I am lucky enough to have a very long wire fence made with spaced and painted steel posts holding a painted steel wire mesh. These posts are held into the ground by means of small & shallow concrete foundations, so to all intents and purposes they are insulated from earth and from one another. The counterweight wire is simply treaded every two meters inside the top of the wire mesh, so the entire counterweight is insulated and floating, running at a height of 2 m approx.

The uploaded pic gives a fair idea of my plant.
Attachments
Modified long wire station plant.jpg
Beverage antenna schematic
Modified long wire station plant.jpg (86.21 KiB) Viewed 2841 times
Fence.JPG
Wire mesh fence supporting the counterweight.
Fence.JPG (305.65 KiB) Viewed 2841 times

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glovisol
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Location: Piedmont, Italy

Re: NOISE ADVANTAGE OF LONG WIRE ANTENNA FAR END TERMINATION

Post by glovisol » Mon May 27, 2019 4:32 pm

THE MODIFIED BEVERAGE ANTENNA PLANT - 2

I now wish to underline the following extremely important points:

1) The ground connections (points A & B) shown in the plant schematic are definitely NOT necessary for receiving system operation (with the counterweight limitation mentioned in point 2 below). They are only safety connections which make sure that the galvanically grounded system does not present a shock hazard to the user. In fact an antenna system, under most local noise conditions, is always best isolated from earth ground. If an antenna system requires an earth ground to deliver the signal, it means that the antenna has technical problems, which, once solved, would make the earth ground connection unnecessary for reception.

2) As we have seen, the input transformer return is made with the counterweight and the receive efficiency of the counterweight, once is properly floating from ground, depends on its size. In other words the counterweight at any frequency should have the same length as the long wire for best efficiency, but this is not always possible. So at LF, say 200 Khz, the earth ground is more efficient than the 80 m counterweight and when at this frequency I use the earth ground as return.

3) The SDRpaly receivers in general and the RSPduo in particular with its balanced input, have proven themselves invaluable for developing the modification of my antenna system. For instance I started testing with a counterweight 20 m long and the receiver provided immediate true received signal strength and noise strength, as well as S/N ratio. As soon as earth ground was disconnected, noise went down, but the same happened with the wanted signals. Consequently the counterweight was increased by adding wire in steps of 10 m: I could see the signal increasing more than noise at every step, until I had to stop at 80 m...because I had run out of wire. At around 40 m I was thrilled to see that the noise had stopped increasing on 14 MHz, but the received signal was increasing. I am sure planning to carry on increasing the counterweight to greater lenghts in the near future.

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sdrom33
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Re: NOISE ADVANTAGE OF LONG WIRE ANTENNA FAR END TERMINATION

Post by sdrom33 » Mon May 27, 2019 6:35 pm

Hi glovisol, thanks for your reply!

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glovisol
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Re: NOISE ADVANTAGE OF LONG WIRE ANTENNA FAR END TERMINATION

Post by glovisol » Tue May 28, 2019 8:41 am

THE MODIFIED BEVERAGE ANTENNA PLANT - 3

The two plant schematics, for balanced inputs and for coaxial inputs, immediately show the value of the balanced input at HF. Not only the balanced input is best fit for the purpose, but by specification and by practical tests (look at my posts on the subject) is significantly more sensitive than the coaxial input. At risk of repeating myself, I judge the balanced input of the RSP Spectrum Processors a notable stroke of genius of the SDRplay Design Team. A long wire antenna trimmed for low noise in many istances shows the balanced input at its best, because of its lower noise figure. In addition the balanced input exhibits a ready made natural rejection to common mode disturbances and makes any connection to noisy stake ground unnecessary.

The receiver termination photo uploaded below shows the antenna arrangements at the receiver's end. Near the building the fence turns at right angles just below the window of the radio room, so it is natural to bring the counterweight wire right into the building with a hole trough the wooden window frame. Another hole brings the antenna lead inside. Both wires go directly to the low noise toroid transformer: simple and effective arrangement.

The aerial 4 photo gives a clear idea of the counterweight arrangement, which now covers all the fence for a length of 80 m. The photo shows I have plenty of room to extend the counterweight along the wine field, something I am planning to do in the near future.
Attachments
Receiver termination.jpg
Antenna & Counterweight arrangenment at the receiver's side.
Receiver termination.jpg (334.02 KiB) Viewed 2752 times
Aerial 4 - Modified antenna.jpg
Close up of the modified 160 m Beverage antenna system.
Aerial 4 - Modified antenna.jpg (216.71 KiB) Viewed 2752 times

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glovisol
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Location: Piedmont, Italy

Re: NOISE ADVANTAGE OF LONG WIRE ANTENNA FAR END TERMINATION

Post by glovisol » Tue May 28, 2019 3:17 pm

NOISE ADVANTAGE CONCLUSION

My experience with the activity described has evidenced the following points.

1) Even in a receiving site with medium to low man made noise and often under the ITU classification of "RURAL" or "QUIET RURAL" area, significant room for improvement can be obtained by careful attention to antenna termination details.

2) Impedance and Return Loss measurements are very useful to assess antenna performance, even though the antenna is used in receive mode only.

3) Antenna termination return to earth ground should be avoided as much as possible, also because noise performance of such terminations is normally unstable and may change at any moment, depending on a great number of factors outside of our control.

4) Most of the ground noise detected and in significant part eliminated by this work seems to be of the electric field, high impedance type: this is proved by the good results obtained by the use of balanced low capacitance ferrite isolation transformers.

5) Finally this antenna with a long counterweight appears similar to a "V" type long wire with two disymmetrical sides and unconventional flare angle. Using this concept there is perhaps room for further improvement.

I am now collecting daily noise readings and will publish 15 days data when available. It will then be possible to compare with data taken (original 135 m Beverage) in November/December 2018.

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sdrom33
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Re: NOISE ADVANTAGE OF LONG WIRE ANTENNA FAR END TERMINATION

Post by sdrom33 » Thu May 30, 2019 4:28 pm

Hi glovisol, I noted that on the schematics you draw one transformer for the HI Z input and two transformers in series for the coax input. Mistake? Why you do this?

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glovisol
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Re: NOISE ADVANTAGE OF LONG WIRE ANTENNA FAR END TERMINATION

Post by glovisol » Fri May 31, 2019 9:19 am

sdrom33, with the HI Z balanced input one balance provider is built inside the RSP 2/duo already, so the single external balancing transformer isolates the RSP receiver input from external dangers, as well as eliminating more common mode also because of its low capacitance between primary & secondary windings.

With the single ended, coaxial input RSP's you are well advised to use two transformers to try and come up to the level of isolation of the HI Z input. Furthermore two low noise transformers in series obviously further reduce the common mode. The RSP's equipped with the HI Z input have of course the additional big advantage of a significantly better sensitivity up to 30 MHz.

Cheers,

glovisol

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glovisol
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Re: NOISE ADVANTAGE OF LONG WIRE ANTENNA FAR END TERMINATION

Post by glovisol » Fri May 31, 2019 9:52 pm

ADVANTAGE @ 1.8 MHz

This evening we had excellent propagation on 1.8 MHz, a good chance to test the advantage on 160 m where the Beverage is just 1 wavelength long and the counterweight half a wavelength long. Noise level was also lower than normal, so there is a small advantage on noise (3 dB) as previously explained, but the advantage in signal strength of this ham station is remarkably high (more than 1 "S" unit) as shown in the screens uploaded below.
Attachments
1.8 MHz compare 1.jpg
Reception @1.8 MHz with counterweight termination
1.8 MHz compare 1.jpg (182.99 KiB) Viewed 2524 times
1.8 MHz compare 2.jpg
Reception @1.8 MHz with stake ground termination
1.8 MHz compare 2.jpg (187.27 KiB) Viewed 2524 times

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glovisol
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Re: NOISE ADVANTAGE OF LONG WIRE ANTENNA FAR END TERMINATION

Post by glovisol » Sat Jun 01, 2019 6:58 pm

Sometimes one is in doubt about the strenght of propagation on a certain ham band. If there are no signals one wonders if it is because of propagation strength being low or nil or perhaps because there are no stations operating. On 40 and 20 m it is easy to tell: if the lower end (CW stations, many with auto calling) is "boiling", propagation is strong in direct proportion to the signal levels here, as shown in the uploaded photos. These levels are low to medium now, but were taken at 19:00 GMT, they will grow to much higher levels in 2 to 3 hours.
Attachments
20 m propagation proof.jpg
Low to medium level propagation, 14 MHz.
20 m propagation proof.jpg (265.91 KiB) Viewed 2475 times
40 m propagation proof.jpg
Low to medium level propagation, 7 Mhz.
40 m propagation proof.jpg (268.59 KiB) Viewed 2475 times

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glovisol
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Re: NOISE ADVANTAGE OF LONG WIRE ANTENNA FAR END TERMINATION

Post by glovisol » Mon Jun 10, 2019 6:50 am

NEW Vs. ORIGINAL ANTENNA TERMINATION - COMPARATIVE RESULTS, 1.8 MHz

As planned, I am now uploading the graph showing the remarkable improvement in Beverage antenna noise floor obtained with the new termination. The new data is compared to original data for October and November 2018 uploaded here:

https://www.sdrplay.com/community/viewt ... 6&start=20

The very unstable and high intensity noise plot of October 2018 was due to exceptionally stormy weather and is not typical. For this reason measurements were repeated in November, with more settled weather and these results can be compared with data taken between the end of May 25 and June 9. The improvement brought about by changing the Beverage antenna terminations is such that now I can listen to the 160 m band daily, while before I could only a few days out of one month. Data for other frequency bands are also ready and will be uploaded next.
Attachments
Noise floor compare 1.8 MHz.jpg
Noise floor compare 1.8 MHz.jpg (81.56 KiB) Viewed 2362 times

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