height of 6 meter beam

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height of 6 meter beam

Postby VK4WTN » Thu Apr 29, 2010 7:12 pm

I am looking at modifying my mini tower (for want of a better word) from about 7m to about 11 m.I am using a YU7EF 6 el yagi. Is it worth increasing the height by 4 or 5 meters to get a lower angle of radiation? And what is the minimum optimum height for a 6meter yagi?
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Re: height of 6 meter beam

Postby VK6OX » Thu Apr 29, 2010 7:39 pm

Hi Wayne,

The short answer is - "the higher the better".

Longer answer: The farther away you can get the beam from any other interfering obstacle, be it trees, buildings, other antennas etc. etc., the more likely you are to have a pattern that is close to design. This is the case for ANY multi-element beam and in general is NOT frequency dependent.

I seem to recall some discussions on minimum "useful" heights which suggested 2-3 wavelengths above ground.

So to return to the short answer - push it higher! :mrgreen:

73 Andy
73
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Re: height of 6 meter beam

Postby VK4TS » Fri Apr 30, 2010 10:33 pm

The optimum height for a six element yagi on flat ground is 30M..... allow for ground advantage at height eg ridges etc benefits disappear beyond 30M so on a site of quick drop off even 10M can be more than enough to obtain optimum performance...
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Re: height of 6 meter beam

Postby VK4WTN » Sun May 02, 2010 8:27 pm

Thanks for the feedback guys, the plan is to get the aerial up about 12- 13m and hopefully we will get a bit better performance.
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Re: height of 6 meter beam

Postby VK3AUU » Mon May 03, 2010 11:03 am

Going from 12 metre high to 30 metres will only give you about 0.25 db more gain in theory, but in practicall terms, the lower angle of radiation may lose you something in the ground clutter so you may mot be better off with the higher antenna. Taking the above into account, your suggestion of 12 metres high with its consequent main lobe at 7 degrees may actually be a better bet than trying to go to the 30 metre optimum height with main lobe at 3 degrees.

David
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Re: height of 6 meter beam

Postby VK4WTN » Mon May 03, 2010 5:40 pm

Thanks for the reply David, I think that 12 meters should be ok, it is also a manageable height at my QTH.Hope to see you on 6 meters over the next few weeks .I have been away working the past few days and missed some of the winter E upenings.Thanks Wayne
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Re: height of 6 meter beam

Postby YU7EF » Fri May 07, 2010 5:29 pm

Wayne

As David said, putting your antenna at 30m above the ground will give you very small benefit in gain and will produce much lower take off angle.
This, in some situations migh be even a setback considering take off angle of incoming signals but another benefit is that "gap" between lobes
in such position is very narrow so you don't have "blind holes" in tour vertical pattern.

Unfortunately can't post radiation pattern diagrams here so you can see the difference but, if you want them, can send them to your mail

In any case, 12m above the ground is more than sufficient (and far easier to handle as well as cheaper) so no real need for more

I worked EME with W7GJ with my antenna at only 6m and made it in just 5 minutes even though I had only 100w and didn't miss any station that
was worked by other guys on Es last Summer - actually worked far more USA stations than most of them, going all the way to mid states such as
Nebrasca. It is much more important to have clear and flat area arround your antenna for at least few km

73, Pop, YU7EF
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Re: height of 6 meter beam

Postby VK4WTN » Sat May 08, 2010 6:34 pm

Thanks for the information Pop.In a built up location it is hard to get aerials much over 15m.So I will get my aerial up to 12- 13m.Your yagi design was really impressive, the SWR curve was exactly as you predicted.They are starting to be a very popular design over here especially without having to use matching devices.If you could send me the lobe patterns at the various heights it would be greatly appreciated.My email address is wazzan1@bigpond.com. Regards Wayne.
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