Simple directional antenna

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silent freq
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Simple directional antenna

Post by silent freq » Fri Jun 07, 2019 11:17 pm

I am researching the possibility of positioning the transmitter in the outskirts of my intended broadcast area. In that case a classic dipole antenna with a circular radiation pattern would spend more than 50% of its power broadcasting outside my intended reception area. I'm not good at making antennas, and a dipole is the simplest I've found.
I've found some paper that claims that if I mount the ground half of my dipole at a horizontal angle and the top half at a vertical angle, then the signal would be directional in the direction the ground half is pointing. Has anybody tried this? -Or do you have any other input on getting cheap and easy directionality?
Here is a link to the paper I found: http://folk.uio.no/tomvs/la4ln/dipole_en.pdf
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Re: Simple directional antenna

Post by nrgkits.nz » Sat Jun 08, 2019 1:33 am

What you need is stacked yagi’s for shaped coverage, a couple of 4 element yagis (including the reflector and driven element) will do the job

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Re: Simple directional antenna

Post by nrgkits.nz » Sat Jun 08, 2019 1:58 am

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Albert H
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Re: Simple directional antenna

Post by Albert H » Sat Jun 08, 2019 2:38 am

If you want hemispherical coverage, the simple "H" aerial works well and works better if you stack a couple of them. This will also give you gain in the direction you want to go in. That's extra radiated power at little added expense!

There are plenty of on-line resources for calculating the sizes of the elements, their spacing, and how far apart each aerial should be if you're stacking them. You'll also have to get into matching stubs and phasing harnesses.

It might sound complicated, but if you have a good SWR Bridge (or - even better - an antenna analyser) and you can test at low power, you'll have little trouble in constructing and aligning something that'll give you great results.
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radionortheast
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Re: Simple directional antenna

Post by radionortheast » Sat Jun 15, 2019 9:34 am

silent freq wrote:
Fri Jun 07, 2019 11:17 pm
I am researching the possibility of positioning the transmitter in the outskirts of my intended broadcast area. In that case a classic dipole antenna with a circular radiation pattern would spend more than 50% of its power broadcasting outside my intended reception area. I'm not good at making antennas, and a dipole is the simplest I've found.
I've found some paper that claims that if I mount the ground half of my dipole at a horizontal angle and the top half at a vertical angle, then the signal would be directional in the direction the ground half is pointing. Has anybody tried this? -Or do you have any other input on getting cheap and easy directionality?
Here is a link to the paper I found: http://folk.uio.no/tomvs/la4ln/dipole_en.pdf
Skjermbilde.JPG
I had sucess with a horizontal radial in the past, you have to coil the coax to stop it acting as an aerial. I have 1 turn of the coax and have also have a break so it isolated below the radial to stop interactions with the mast, its a very good aerial, I have the radial pointing at 45 degree angle, works very well in a receiver specially with it horizontal. For it been directional it is omidirectional, I found out where to coil the coax with low power using a scanner nearby and also find the best angle of the radial..

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Re: Simple directional antenna

Post by silent freq » Sun Jun 16, 2019 7:36 pm

First of all, thank you all for taking your time to answer my question. Even though I come with more questions it does not diminish the fact that I am very grateful.

@nrgkits.nz: I'm a fat construction worker, and plan to climb as high up in a nearby tree as I can get and fasten the aerial with cable ties. So the 4 element yagi seems out of the question. Are there any solutions that are more portable?
@Albert H: I can't seem to google my way to a DIY instruction on constructing a simple H Aerial. Could you please point me in the right online direction?
@radionortheast: Does this mean that the solution in the attached paper in the original post does NOT give a more directional broadcast than a normal Dipole? And a second question: Does the coil work as a balun? (not that I understand how baluns work, they seems like witchcraft to me)

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yellowbeard
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Re: Simple directional antenna

Post by yellowbeard » Sun Jun 16, 2019 9:30 pm

Did you want help or just bants? Assistance here is inversely proportionate to attitude. You are ripping on guys that know a lot more than you or me, they may not reply to your posts in future. Make one of these:
https://web.archive.org/web/20130910092 ... /hb9cv.php
Mounted vertically you should get a radiation pattern like this:
Image
Your alternative is to buy a receiving yagi and put a 4:1 coax balun on it.

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silent freq
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Re: Simple directional antenna

Post by silent freq » Mon Jun 17, 2019 12:40 pm

OH, I am so so sorry, I really didn't try to offend anybody, really I didn't. That's why i started by expressing my gratitude. I am really thankfull for the help they are offering, and I can only blame any unintended insults to the fact that I am not a native English speaker.

I really liked the characteristics of the yagi, but the physical size, did not fit my physical limitations (which I had not stated in the original post).
Given Albert H's track record I really wanted to follow his advise, but was unable to find anything useful. I asume this comes down to my lack of some basic knowledge.
And I simply wanted to ask Radionortheast some followup questions since he had worked with the antenna I originally planned to build.

I am now going to read all I can find about the antenna suggested by Yellowbeard. And I am very grateful for this sharing of your knowledge.

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Re: Simple directional antenna

Post by NOYB » Mon Jun 17, 2019 3:52 pm

Don't beat yourself up Mr Silent Freq. I re-read your post and could not see anything offensive.

Basically you have to trade more metal in the air to get gain - which may make the antenna more difficult to install, and more visible to inquisitive eyes. If you make your own, unless you know what you are doing it is quite possible you make things worse. I'm a bit sceptical about your original heath-robinson dipole idea - if it does give directivity there is a danger it gives directivity in the wrong direction - maybe up into the sky!

Remember "height is might" on FM - so if you get a nice high antenna location and get the coverage you need where you want it, to a certain extent "who cares" if it also goes in other directions that you don't need? 50% is only 3dB which is quite difficult to detect driving round on a radio.

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yellowbeard
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Re: Simple directional antenna

Post by yellowbeard » Tue Jun 18, 2019 5:21 pm

Yes apologies - you are right and I am wrong. I misread your phrasing, sorry bout that! :oops:
By way of a peace offering, you may want to see these 2 Metre antennas:
http://www.iol.ie/~yellowbeard/zlspecial.html
http://www.creative-science.org.uk/2m_5 ... ecial.html

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Re: Simple directional antenna

Post by teckniqs » Wed Jun 19, 2019 5:41 am

NOYB wrote:
Mon Jun 17, 2019 3:52 pm
50% is only 3dB which is quite difficult to detect driving round on a radio.
I thought 50% was 1.5dB

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radionortheast
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Re: Simple directional antenna

Post by radionortheast » Thu Jun 20, 2019 6:59 pm

silent freq wrote:
Sun Jun 16, 2019 7:36 pm
@radionortheast: Does this mean that the solution in the attached paper in the original post does NOT give a more directional broadcast than a normal Dipole? And a second question: Does the coil work as a balun? (not that I understand how baluns work, they seems like witchcraft to me)
I think the difference will problaly only be marginal, with mine with the radial at 45 degree angle moving aerial round theres hardly any change of the signal on my scanner. I did get the aerial working with radial in horizontal mode in the past, reception was very good over 4 surrounding towns, you couldn’t notice any directivity.

I do get a decrease in signal with the radial horizontal, if I tilt it the L shape over to 45 degree angle the signal gose up, if you really wanting to do it that would be the thing to try, to stop in raidiating to a higher elevation. In some ways the 1 radial aerial is very much like a dipole, not having a balun could give lower than expected performance.

Balus do work, i’ve coiled the coax behide dipoles in the past, it works for stoping the signal going back down the coax, I tend to find theres a sweet spot. When i’ve made dipoles and put a reflector be-hide them, I still get a signal in most directions, its very hard to stop a signal going where it shouldn’t be going..a big directional aerial will be better but you can't go putting that in a tree, it might be worth trying the L shaped aerial!

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Re: Simple directional antenna

Post by Albert H » Fri Jun 21, 2019 12:50 am

Get a map of the area you want to cover. Calculate the beam angle you need. Also calculate the downward tilt you'll need to get to the middle of the target area. Let us know what these angles are, and I'll be able to recommend suitable aerials that are easy to build and match.
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Re: Simple directional antenna

Post by NOYB » Fri Jun 21, 2019 10:57 am

teckniqs wrote:
Wed Jun 19, 2019 5:41 am
I thought 50% was 1.5dB
20log P1/P2

eg comparing 50w to 100w (50%):-
20 log(50/100) = -3.01dB

Sad radio engineers like me carry the key ratios around in their head:

2 - 3dB
3 - 5dB
4 - 6dB
10 - 10dB

Then you can combine these to work out other ratios. eg: 13dB is a combination of 2 and 10 - ie: a ratio of 20. 20dB is 10 and 10 - ie: 100
etc.

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