LW-MW-SW Relay Tuned 15' Noise Reducing Vertical Antenna

Useful information regarding antennas for SDR products.
glovisol
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Location: Piedmont, Italy

Re: LW-MW-SW Relay Tuned 15' Noise Reducing Vertical Antenna

Post by glovisol » Wed Jul 10, 2019 7:22 pm

Hi Paul, I wish to correct my statement on the abnormal difference in sensitivity between the HI Z and the 50 Ohm input. This has been caused by an unsuitable transformer used on the 50 Ohm input, because being far from home I have very limited resources here. I hope to get suitable 50 Ohm transformers soon. In any case this seems to point to the fact that the transformer termination of the antenna is extremely critical.

Apologies for this mistake.

Gianfranco

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vk7jj
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Re: LW-MW-SW Relay Tuned 15' Noise Reducing Vertical Antenna

Post by vk7jj » Wed Jul 10, 2019 11:52 pm

Hi Gianfranco,

You asked me to model your pallet, here it is over real ground at a height of 16m:

Overview showing current flow (the blue lines) is equal in all four sides
Feedpoint is the red dot.
modelview.png
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The pattern is omni with useful lowish angle lobes that are giving you all that nice activity
pattern.png
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40m (7.15MHz) antenna characteristics
7MHz.png
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Forgive my screen pic dump quality; the Mac 4K screen dumps at 144dpi resolution and those images get resampled to presumably 72dpi and become annoyingly unsharp.

Thanks for the kind comments from you and sdrom33 but the truth is VK7JJ is just another flawed wannabe standing on the shoulders of giants like Cebik, waving a little flag and pointing to things he's borrowed from them; much better to go straight to the giants themselves.

Its really great to see you and Paul going at it!

Phil

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vk7jj
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Location: Tasmania

Re: LW-MW-SW Relay Tuned 15' Noise Reducing Vertical Antenna

Post by vk7jj » Thu Jul 11, 2019 12:05 am

Here it is again at 6m (51MHz) and UHF (432MHz) to show how a loop is good for wide band work.

You'll note the gain, something you will not get from a vertical whip or groundplane, along with the improved radiation resistance and reactance.

The angle of radiation is actually better than a vertical, vertical patterns break up into even higher angle lobes as you go up in frequency. The old ham chat about a kite with a kilometre long wire being the ultimate HF antenna - maybe so if it was caught in a tree about one kilometre away.
Screen Shot 2019-07-11 at 10.00.44 am.png
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Screen Shot 2019-07-11 at 9.59.55 am.png
Screen Shot 2019-07-11 at 9.59.55 am.png (145.36 KiB) Viewed 3530 times
Phil

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Paul
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Re: LW-MW-SW Relay Tuned 15' Noise Reducing Vertical Antenna

Post by Paul » Thu Jul 11, 2019 4:58 am

Hi Gianfranco
Thanks for the update.

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Paul
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Re: LW-MW-SW Relay Tuned 15' Noise Reducing Vertical Antenna

Post by Paul » Thu Jul 11, 2019 5:12 am

Hi again Gianfranco
A further question if I may please:
Should this antenna work on a flat surface?
Pardon the obvious ignorance.

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glovisol
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Re: LW-MW-SW Relay Tuned 15' Noise Reducing Vertical Antenna

Post by glovisol » Thu Jul 11, 2019 5:57 am

Hi Phil & Paul,

1) Very many thanks for the modeling @ 7 Mhz, which is mid-band, as the antenna works fine down to 3.6 and up (best at 14 MHz). The transformer at present is 450 to 1000 Ohm. From your data, at last @ 3.6 MHz, it should be rather 200 to 1000 Ohm, but Z data up to 14 MHz should be necessary. Since noise is really low (with the transformer) the best match will surely increase antenna efficiency.

2) Best performance at 3.6 MHz is with antenn placed horizontally on the vertical metal railing you see in the photo.

3) On 7 & 14 MHz the antenna works both in a horizontal & in a vertical position l and exhibits some limited directivity. Limited probably because the narrow space on the balcony does not allow me to neatly manipulate it.

4) Yesterday evening I contated my supplier who is now sending me a few ferrite toroids & copper wire, so I shall be able to build suitable transformers, which seem the most critical part of the antenna.

5) The precision measurement of one side of the square (dictated by the salvaged planks) length is 88 cm.

Kind regards,

Gianfranco

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vk7jj
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Re: LW-MW-SW Relay Tuned 15' Noise Reducing Vertical Antenna

Post by vk7jj » Thu Jul 11, 2019 11:40 am

The modelling only takes a few moments, glad to help, here is 80 and 20m
80m.png
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20m.png
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80-20.png
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If you can find some zip cord or make a simple twisted pair feed from antenna wire or better still find some old TV ribbon, before you get the ferrites, it would be a waste to try to fine tune the ferrite with the coax feed. It looks like coax.

Phil

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glovisol
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Re: LW-MW-SW Relay Tuned 15' Noise Reducing Vertical Antenna

Post by glovisol » Thu Jul 11, 2019 3:18 pm

Phil,

It is not coax at all, it is a short section of electrical twin wire, like zip cord. I wish I had coax here, I have nothing!!

Thank you for your calcs. The picture I see is quite simple:
Antenna loop calc.png
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Attachments
Studying VLF underwater propagation....jpg
Studying VLF underwater propagation....jpg (138.17 KiB) Viewed 3424 times
Last edited by glovisol on Sun Jul 21, 2019 3:51 pm, edited 3 times in total.

vk7jj
Posts: 206
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Location: Tasmania

Re: LW-MW-SW Relay Tuned 15' Noise Reducing Vertical Antenna

Post by vk7jj » Fri Jul 12, 2019 4:54 am

Hi Gianfranco, fine on your twin wire, thank you for putting me out of my misery. But then you put me right back into a worse state of misery showing that photo of you in the water during our mid winter! Totally callous.

Fine on your matching considerations and hopefully your ferrites will meet expectations, that would be really good. I wonder if you have any other antenna available where you are or if you put the pallet to use because you had no other? A comparison with a known antenna would be interesting.

I hope you're still itching to build a decent sized loop when you get home and you can put that up against your low noise Beverage antenna.

Phil

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glovisol
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Re: LW-MW-SW Relay Tuned 15' Noise Reducing Vertical Antenna

Post by glovisol » Fri Jul 12, 2019 1:37 pm

Hi Phil, I slept on it and was even more convinced this morning, so here is my idea, which is probably the re-invention of the wheel, or perhaps there will be 999 reasons why it will not work. I only have to wait until I get back home in August and test it.

METHOD FOR PASSIVE BROADBAND MATCHING OF A SMALL LOOP ANTENNAS IN HF

This method is based on original work by Philip R. Geffe (Simplified Modern Filter Design) who, as far as I know, was the first (in the fifties) to publish the idea that filter networks can be used not only for frequency band limiting, but also for broadband impedance matching. In his book Geffe gives tabulations for normalized elements of filter neworks working between different input / output impedances. Far more complete tables have been published later by Saal and by Zverev. For complete reference information, look here:

https://www.sdrplay.com/community/viewt ... 026#p16026

Looking at the equivalent circuit of a small single turn loop, we see that it is represented by a resistor of a very low, sub-Ohm value, in series with an inductor. If we consider an useful frequency band extending from 3 to 15 MHz, we see that the median values are R=0.56 Ohm and L=4.6 uH and that the spread is relatively small. It must be noted here that I calculated the loop inductance with another independent formula (*) and I found the same value as given by Phil.

Now my idea is very simple:
a) if I take a simple Butterworth or Chebyshev prototype, say N=5 and
b) de-normalize it @ 15 MHz (or any frequency above the reception range I want from my loop) and
c) also de-normalize between 0.56 Ohm input and a convenient higher output impedance and
d) if the first series inductor has a calculated value higher than the antenna inductance,

THEN

e) I can incorporate the loop inductance into the value of the first network inductor and
f) Obtain perfect wideband match between 3 and 15 MHz without resonating the loop.

I shall now test the idea by calculation and if there is a significant number of simple networks that fulfill the conditions described above, I shall show them next.

(*) Inductance L = 0.008 * s * ln(s/l + 0.37942 + (0.333 * l/s)) = 4.29569 uH

Where:
L: inductance in uH
s: side length, cm = 88
l: coil length = wire diameter cm = 0.2

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