antenna height vs number of elements

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antenna height vs number of elements

Postby VK6KFD » Thu Dec 10, 2009 8:11 pm

Hi - some help here please.
I have poor QTH being on the west side of a fairly large hill. Amateurs on the other side of the hill and who are within a few ks are consistently 5s points better than me (when I can hear anything). I am using a 5 element home brew antenna. I cannot really go much higher on my mast. Is it worth the effort / expense to get a better antenna or am I geographically doomed, so to speak? Relocating the qth is not an option at the moment. thanks - Frank VK6kfd
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Re: antenna height vs number of elements

Postby VK4MDX » Thu Dec 10, 2009 9:04 pm

Well, firstly I am just a beginner in the six meter realm, but I read lots :-). I would have thought height would not be that critical on 6m, and terrain while limiting would not be that big a deal, not the 5S points you mention anyway.

Have you optimised the antenna using a field strength meter? Are you sure it is working to maximum efficiency for the design?

David
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Re: antenna height vs number of elements

Postby VK6KFD » Thu Dec 10, 2009 10:58 pm

No David - I have not optimised it apart from tuning for minimum swr. I do not have access to a field strength meter and being just 1 km from the coast I am pretty well shielded from all other 6m operators in Perth from the NE to S so hard to do a comparison. Last summer season was particularly frustrating. Thanks for the suggestion i will look into it.
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Re: antenna height vs number of elements

Postby VK4MDX » Thu Dec 10, 2009 11:06 pm

OK. It could be worth your while, as I and friends have found critical differences can arise from even very slight design variances in yagis, particularly at 6m. Could be well woth your efforts. Perhaps a starting point would be to revisit your original design for the yagi and remove any, even slight variations.

Cheers

David
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Re: antenna height vs number of elements

Postby ZL1RS » Fri Dec 11, 2009 4:57 am

Hello Frank,

Depending on the radio, 5 "s-units" may not be many dB. The calibration on s-meters (especially below "S5") is generally poor ... some that I have measured had "s-units" around 2dB apart at the lower end of the scale .

Signals can arrive from the ionosphere at all sorts of angles, but it is generally accepted that a low horizon gives better results. To get a better idea of the obstruction, how high is the hill? ... and, how close is it?

Probably the most telling indication of what effect that the hill might be having ... have you compared with the other locals signals coming from directions where the hill is not in the way?

73, Bob
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Re: antenna height vs number of elements

Postby VK3AUU » Fri Dec 11, 2009 7:17 am

Just build a bigger bird perch, 9 or 10 elements on 6 metres should be within the competence of anyone these days. Go to VK5DJ's web page for details of a 10 element DL6WU and you can't go wrong.

David
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Re: antenna height vs number of elements

Postby VK3BJM » Fri Dec 11, 2009 7:20 am

Frank, perhaps you could also confirm for us what height above the ground the Yagi is, and length/type of feedline between Yagi and radio?

73,
Barry
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Re: antenna height vs number of elements

Postby VK4APN » Fri Dec 11, 2009 8:52 am

http://radiomobile.pe1mew.nl/ - RF propagation simulation software

Apart from ensuring your antenna, feedline etc are working properly ..... The software above will provide you with a picture of what is possible from your exact location. There is a quick start page on how to use the software by a G land amateur, if I can find the link I will post it.
The software takes a fair bit of work to start with, but in the end you can plug in antenna gain, height, power, feedline loss etc etc, alter freqency and bands and "see" on a map the likely propagation paths - it will even export an overlay onto google maps. The program loads topographical info automatically. You need to know your exact lat/long or locator. If you know the exact locator, lat/long of other staions of interest you can plot between them even multiple stations.

I have used it to accuratetly predict / confirm vhf/uhf paths in my area. It is an interesting tool and very informative.

And its FREE.

http://www.g3tvu.co.uk/Quick_Start.htm found it.....
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Re: antenna height vs number of elements

Postby VK4ABW » Fri Dec 11, 2009 11:13 am

great program there Paul. this is the picture it showed of what i can work:
picture.jpg
picture.jpg (14.62 KiB) Viewed 947 times

:D
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Re: antenna height vs number of elements

Postby VK4APN » Fri Dec 11, 2009 11:54 am

vk4abw wrote:great program there Paul. this is the picture it showed of what i can work:
picture.jpg

:D


Mea Culpa Gary - I should have been more specific regarding the software capability. Sorry.

The software mentioned in my original post is for "terrestrial" use only.
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Re: antenna height vs number of elements

Postby VK6OX » Fri Dec 11, 2009 11:56 am

Frank would be at most a km west of me, and I can understand his frustration. When looking East, he's beaming into a substantial sand hill, upon which I'm located.

Frank, I might be able to find some time to help you optimise your antenna - email or skype me, my details are under "Operator Info" on the VKLogger. :)

73
Andy
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Re: antenna height vs number of elements

Postby VK6KFD » Sat Dec 12, 2009 10:03 am

Thanks everyone for your feedback and suggestions which i will follow up now that I am on holidays (yay!) My antenna is 5 m high which takes it above the peak of my roof line by 2m. My "shack" is close to the mast so I have no more than 15m of RG213 coax feed. The height of the hill is a bit harder to quantify. I am 200m from the brow of the hill. My antenna barely clears the top of the roof of the house on the other side of the cul de sac. There would be another 2 houses on top of that as you go up the hill. The local beacon is S7 on both my IC560 & IC706. Thanks for the offer of help Andy - will be in touch. Frank
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Re: antenna height vs number of elements

Postby VK5PJ » Sat Dec 12, 2009 4:16 pm

Hi Frank,

VK6KFD wrote:Thanks everyone for your feedback and suggestions which i will follow up now that I am on holidays (yay!) My antenna is 5 m high which takes it above the peak of my roof line by 2m. My "shack" is close to the mast so I have no more than 15m of RG213 coax feed. The height of the hill is a bit harder to quantify. I am 200m from the brow of the hill. My antenna barely clears the top of the roof of the house on the other side of the cul de sac. There would be another 2 houses on top of that as you go up the hill. The local beacon is S7 on both my IC560 & IC706. Thanks for the offer of help Andy - will be in touch. Frank


I too have a "pesky hill" but mine is to the west of me, given that your antenna barely clears the roofline of the house, I think you may need to start there and for the time being ignore the hill (which you can not change) and concentrate on what you can alter and finding a few more metres of height would be of #1 concern, so you can at least clear the local roof tops. I am about 150 metres below my pesky hill top here and it is about 900 metres away from me. It realy hurts on 144 MHz but is just noticable on 50MHz BUT I suspect it would be far nastier if the antenna was not in the clear at home.

Good luck with your endeavours.
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Re: antenna height vs number of elements

Postby VK6KFD » Sun Dec 13, 2009 10:11 am

Hi Peter et al. Its not the height of the hill so much its the closeness of the QTh to the summit or pitch I guess. With summer approaching I am looking for a "quick fix" without having to drop the whole set up and put it back up. I think with suitable supports to the wall i will be able to push it up from the bottom and add another 2- 3 m to the overall height. At least I will be able to see if that makes any difference before I try any serious modifications or buy a crank up tower. Thanks to everyone for their comments. Look out for me on 6 (weak signal!) 73's Frank
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Re: antenna height vs number of elements

Postby VK3AIF » Sun Dec 13, 2009 1:12 pm

Hello Frank and others,

The following observation may give you something to consider.

I have 2 identical 2m antennas, one mounted at 6 M the other at 10 M. The terrain around here is substantially flat with the surrounding hills being only a few degrees at worst above the horizon, there are numerous trees in all directions of varying heights some above the level of both antennas.

The higher antenna outperforms the lower one by about 11 db and only 1 of the reference signals is higher on the lower antenna out of 11.

I assume the the increase in signal is more due to having less foliage in the path than the added height could account for alone. I was astounded by this result and to me it confirms the old adage "Height is Might".

Another possible consideration but untested by me is if you were to increase your antenna gain, perhaps more of the signal would be directed directly into the offending hill and be absorbed because of the narrower beamwidth and result in even less radiation in that direction?

Hope this is of some use and good luck with your problem.

Dave
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Re: antenna height vs number of elements

Postby VK4TS » Sun Dec 13, 2009 3:12 pm

Frank - its like this....no matter what we say if you cant go higher and you dont want to change location no miracle cure will work..

Dx and I am assuming you are referring to that; comes in best at low angles consistently and to achieve low angles you need height and clear horizons..anything else is a compromise..more gain will make a salesman happy but it will all be pushed into the side of the offending ridge...

Moving is your best option...preferably to the top of the hill and then get the antenna up and in the clear..I have done extensive modelling on this and optimum on HF bands is 2 wavelengths plus (surprisingly there is little difference in Yagi size vs optimum angle) - take into account slope of the land as well as that adds to antenna height..

Look at these really good stations EF8M, CR3E, D4B, HC8N and the common thing is they are on hill tops and this is why they are amongst the top HF contest stations..this does translate to 6M...if you want to work DX consistently you need at least 20M of height in the prevailing direction..this could be from 10M tower and 10M of ridge but it all adds up.

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