NOISE ADVANTAGE OF LONG WIRE ANTENNA FAR END TERMINATION

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

Post by glovisol » Tue May 14, 2019 7:34 am

No text in this first post due to amendment difficulties. Please look at posts following.

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glovisol
Posts: 662
Joined: Thu May 10, 2018 6:42 pm
Location: Piedmont, Italy

Re: NOISE ADVANTAGE OF LONG WIRE ANTENNA FAR END TERMINATION

Post by glovisol » Tue May 14, 2019 8:09 am

NOISE ADVANTAGE OF LONG WIRE ANTENNA FAR END TERMINATION

FOREWORD ADDED 24/05/20219

It is common knowledge that a receiving system is only as good as its antenna. In our times, when man made noise avoidance has become a most important issue, we can rightly say that an antenna is as good as its termination. In most general terms a receiver is a two input terminal electrical device and to function it must be connected to a two terminal output device: the antenna. So the long wire antenna must always be considered with two terminals: one is the antenna proper, the other is the counterweight. Note that I did not write "ground", but "counterweight". At the beginning of Radio Technology, there was little or no man made noise and reception had to cope with galactic and atmospheric noise only. In these conditions the counterweight terminal had no real importance, a good ground would suffice and the better or the larger antenna would deliver more signal + galactic noise + atmospheric noise to the receiver. In our times, with man made noise, this is no longer true, because the quality of the counterweight determines the amount of man made noise the antenna delivers to the receiver. A well designed antenna with the right counterweight will deliver not only more signal to the receiver, but also less noise: this is the paradox the present thread is all about.


In mid April a big storm broke at ground level the telephone pole supporting the end of my 135 m Beverage antenna. This antenna is described in detail here and has been used for most material published on this Forum.

https://www.sdrplay.com/community/viewt ... 2&start=40

A few days ago the antenna re-installation was completed and the antenna length was increased from 135 to 160 m, thereby making it a full wavelength @ 3.8 MHz. Here below are the characteristics of the modified antenna.

BEVERAGE ANTENNA MODEL CHARACTERISTICS & SPECIFICATIONS
Antenna length: 160 m.
Antenna supports: Receiving end, house wall with triple purchase tensioner & ceramic insulator.
Termination end: Telephone type wooden pole.
Antenna drop, receive side: 5m. Termination side: 5.5 m.
Antenna termination: 560 Ohm (10 resistors 5.6 KOhm in parallel). Termination is shown in Figure 1.
Antenna wire: plastic coated, 10 strand, brass plated steel wire. Each strand 0.3 mm dia. Total conductor diameter: 3 mm.
Total wire diameter with insulation: 4,5 mm. Wire resistance: 210 mOhm/m. Total antenna resistance:(160+5+5.5)*0,210 = 35.8 Ohm.
Average antenna height over ground between supports: 6 m.

I have uploaded here for convenience the original photo in Figure 1, as the antenna has apparently the same termination arrangement. In reality it was decided to dig a much deeper ground, using two 1.8 m long steel grounding stakes in series. The top of the first stake and the pointed bottom of the second stake were drilled to accept 8mm dia. screws. The first stake was hammered in place, then the second stake was joined to the first and the entire assembly hammered down to obtain a ground depth of 3.5 m.

The first test was done with no far end termination, followed by a second with the termination connected and with receiver termination switching. The antenna noise difference between terminations switching was so large as to become immediately apparent, and many more tests have been done in the last few days, as will be described in the following posts.


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Attachments
Termination.JPG
FIGURE 1. Beverage antenna far end termination.
Termination.JPG (213.98 KiB) Viewed 5879 times

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glovisol
Posts: 662
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Location: Piedmont, Italy

Re: NOISE ADVANTAGE OF LONG WIRE ANTENNA FAR END TERMINATION

Post by glovisol » Wed May 15, 2019 6:02 pm

At present I am collecting antenna noise data for the next two weeks, in order to compare with previous uploaded data. I have decided to proceed in this fashion, as data collected over only a few days could lead one to wrong conclusions.

In the meantime I have done Network Analyser measurements on the terminated antenna, that show how the Beverage is a true travelling wave, wideband device, covering the entire frequency spectrum from 100 KHz to 29 MHz with fairly constant impedance and quality return loss. Uploaded below results 0-600 KHz.
Attachments
3. TRM 0-600 KHz-Z.jpg
3. TRM 0-600 KHz-Z.jpg (106.82 KiB) Viewed 5778 times
2. TRM 0-600 KHz-RL.jpg
2. TRM 0-600 KHz-RL.jpg (87.59 KiB) Viewed 5778 times
1. TRM 0-600 KHz-SWR.jpg
1. TRM 0-600 KHz-SWR.jpg (80.07 KiB) Viewed 5778 times

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glovisol
Posts: 662
Joined: Thu May 10, 2018 6:42 pm
Location: Piedmont, Italy

Re: NOISE ADVANTAGE OF LONG WIRE ANTENNA FAR END TERMINATION

Post by glovisol » Sat May 18, 2019 6:04 am

Uploaded below results 500 - 2500 KHz.
Attachments
6. TRM 500-2500KHz-Z.jpg
6. TRM 500-2500KHz-Z.jpg (108.76 KiB) Viewed 5682 times
5. TRM 500-2500-RL.jpg
5. TRM 500-2500-RL.jpg (90.75 KiB) Viewed 5682 times
4. TRM 500-2500KHz-SWR.jpg
4. TRM 500-2500KHz-SWR.jpg (83.47 KiB) Viewed 5682 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 » Sat May 18, 2019 6:07 am

Uploaded below results 2500 - 7500 KHz.
Attachments
9. TRM 2500-7500-Z.jpg
9. TRM 2500-7500-Z.jpg (107.21 KiB) Viewed 5682 times
8. 2500-7500-RL.jpg
8. 2500-7500-RL.jpg (88.08 KiB) Viewed 5682 times
7. TRM 2500-7500 -SWR.jpg
7. TRM 2500-7500 -SWR.jpg (83.8 KiB) Viewed 5682 times

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glovisol
Posts: 662
Joined: Thu May 10, 2018 6:42 pm
Location: Piedmont, Italy

Re: NOISE ADVANTAGE OF LONG WIRE ANTENNA FAR END TERMINATION

Post by glovisol » Sun May 19, 2019 6:48 am

Uploaded below results 7500 - 15000 KHz.
Attachments
12- 7500-15000-Z.jpg
12- 7500-15000-Z.jpg (108.79 KiB) Viewed 5594 times
11. 7500-15000KHz-RL.jpg
11. 7500-15000KHz-RL.jpg (91.99 KiB) Viewed 5594 times
10. 7500-15000 KHz-SWR.jpg
10. 7500-15000 KHz-SWR.jpg (85.27 KiB) Viewed 5594 times

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glovisol
Posts: 662
Joined: Thu May 10, 2018 6:42 pm
Location: Piedmont, Italy

Re: NOISE ADVANTAGE OF LONG WIRE ANTENNA FAR END TERMINATION

Post by glovisol » Sun May 19, 2019 6:51 am

Uploaded below results 15000 - 29000 KHz. Comments and termination optimisation to follow.
Attachments
15. 15000-29000-Z.jpg
15. 15000-29000-Z.jpg (115.73 KiB) Viewed 5594 times
14. 15000-29000KHz-RL.jpg
14. 15000-29000KHz-RL.jpg (92.78 KiB) Viewed 5594 times
13. 15000-29000KHz-SWR.jpg
13. 15000-29000KHz-SWR.jpg (94.55 KiB) Viewed 5594 times

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glovisol
Posts: 662
Joined: Thu May 10, 2018 6:42 pm
Location: Piedmont, Italy

Re: NOISE ADVANTAGE OF LONG WIRE ANTENNA FAR END TERMINATION

Post by glovisol » Wed May 22, 2019 4:53 pm

BEVERAGE ANTENNA TERMINATION - 1

Contrary to general opinion, long wire antennas in general and Beverage antennas in particular are not easy to optimise, because their simple form is deceiving. The general optimistic belief is that, once you have the wire to spool out and the land to lay it on, then you have a good antenna, the best for optimal listening work in all of LF and HF range. Here below is a synthesis of the problems one must overcome to reach this end.

The Beverage antenna requires to be laid at a relatively low height on poor and lossy ground. At the two extremities we have the far end, away from the receiver, and the receiver end.The antenna is vertically polarized and because of the earth underneath it has a low radiation angle, ideal for long distance work in HF for wire lengths of one wavelength or more. The antenna has a good directivity out of the far end, provided it is terminated with a resistor of suitable value. Thus the first point requiring attention is the far end termination. The receiver end is connected to the receiver's input and here we meet the biggest difficulties, caused by the antenna return lead.

Somebody like me, with little experience in long wire antennas, in July 2018 planted two ground stakes, 1.8 m in depth (one at the far end, to connect the load resistor and another at the receiver end, to connect the N terminal on the HI Z input of my RSPduo) and happily started using his big "Beverage":

https://www.sdrplay.com/community/viewt ... 2&start=20

In the course of the first few tests it became evident that an isolation transformer was more than necessary and I immediately discovered the vertues of low capacitance ferrite transformers, but my antenna development stopped here. If somebody had come along telling me that with some study and care I could get a worst case received noise improvement of 6 dB (and much more when local noise gets really bad) by looking at the antenna terminations, I would have not believed it. I was so happy with my antenna I even decided to do noise measurements for assessing receiver system performance:

https://www.sdrplay.com/community/viewt ... 6&start=30

It is fortunate that we now have these measurements for comparison to assess the noise/sensitivity variations with the modified and improved antenna.
Attachments
7 MHz noise compare.jpg
Over 6 dB noise advantage with modified antenna terminations on 40 m.
7 MHz noise compare.jpg (198.93 KiB) Viewed 5301 times

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glovisol
Posts: 662
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Location: Piedmont, Italy

Re: NOISE ADVANTAGE OF LONG WIRE ANTENNA FAR END TERMINATION

Post by glovisol » Thu May 23, 2019 9:11 am

BEVERAGE ANTENNA TERMINATION - 2

- THE FAR END TERMINATING RESISTOR
Theory and software modelling place the impedance of the Beverage antenna at a value between 500 and 600 Ohm, depending on wire altitude over ground and soil characteristics. The previously uploaded test results, done with 560 Ohm at the far end, show that the parallel equivalent resistance is between 300 and 600 Ohm, depending on frequency and that the parallel equivalent capacitance is fairly constant and in the order of 10 to 20 pF. Both resistance and capacitance increase at lower frequencies, where the antenna length to become shorter than one wavelength. The test results show that there is a optimum value of terminating resistor which is the best compromise between the impendance value extremes.

The uploaded screens below and in the following post show what happens changing the terminating resistor from 560 to 390 Ohm: VSWR becomes worse at low frequency and better at 29 MHz, so probably the best compromise for an average antenna height of 6 m above ground is a value around 450 Ohm.
Attachments
F. Compare 0-500.jpg
F. Compare 0-500.jpg (58.37 KiB) Viewed 5234 times
G. Compare 500-2500.jpg
G. Compare 500-2500.jpg (60.04 KiB) Viewed 5234 times
H. Compare 2500-7500.jpg
H. Compare 2500-7500.jpg (57.36 KiB) Viewed 5234 times

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glovisol
Posts: 662
Joined: Thu May 10, 2018 6:42 pm
Location: Piedmont, Italy

Re: NOISE ADVANTAGE OF LONG WIRE ANTENNA FAR END TERMINATION

Post by glovisol » Thu May 23, 2019 9:14 am

BEVERAGE ANTENNA TERMINATION - 2

- THE FAR END TERMINATING RESISTOR


Here below VSWR results compared.
Attachments
A. Compare 0-500.jpg
A. Compare 0-500.jpg (46.91 KiB) Viewed 5233 times
B. Compare 500-2500.jpg
B. Compare 500-2500.jpg (47.78 KiB) Viewed 5233 times
C. Compare 2500-7500.jpg
C. Compare 2500-7500.jpg (49.54 KiB) Viewed 5233 times

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