Your ideas of optimum height for a 6m antenna

[VK4QB]

Hi Guys,
What are your feelings of the optimum height that a 6 metre antenna should be ? Obviously we can have it on a mountain top, but hey, lets be practical.
Brian 4QB

[VK3AUU]

That is an interesting question Brian. First of all, you need to consider what happens when you raise or lower an antenna above real ground. In my case, on 6 metres, at a height of 10.5 metres the primary lobe due to ground reflection is at 8 degrees with a theoretical gain of just under 21 dbi. The secondary lobe is at 22 degrees with a gain of 13 dbi. Actual gains will be something less. In the hemisphere from north west around through east to south east there is also a measured ground lobe, probable gain probably something less than 16 dbi due to the presence of trees. This low lobe is somewhat diminished in the other hemisphere due to the open nature of the terrain, so that the ground reflected lobes predominate.

If you double the height of the antenna to 21 metres, (no mean feat) the main lobe gain will increase by about 0.6 db and will come down to 4 degrees. Other lobes will then be found at 12 and 20 degrees with gains around 20 and 16 dbi respectively. (Sun noise measurements on two metres have shown that the second lobe may be better than the first lobe due to absorption of ground vegetation when the antenna is above 5 wavelengths above the ground))

Even higher will result in progressively lower angles and probably more useful lobes, so the answer to the question is probably, "The higher the better", but due to financial and physical constraints you do the best that you can under the circumstances.

Incidentally, the quoted angles are largely determined by the height of the centre of the array above the ground, regardless of whether the antenna is composed of stacked members or not.

[VK4QB]

Thank David ,
Funnily enough, Roger 2ZRH has a topic on the logger pertaining in a way to this question.
Brian 4QB

[VK2EM]

When I worked the USA, and up to 32 JA's in an opening in 30 minutes (several times), my 3 element yagi was only 6 metres high, and I only had about 50W reaching the antenna. I was on a block surrounded by trees. Its a case of "if they want to hear you, they will"

[VK2ZRH]

Returning to Brian's original question: the lower you can get the first (vertical plane) lobe, the better; this will help with low ray path angles on propagation types such as Es and TEP.

The drawback is that the first null between the first and second vertical plane lobes will be a disadvantage for signal ray paths coming in at slightly higher angles.

Modelling will illustrate the principles [see VK2ZTO posting at viewtopic.php?f=43&t=8251&start=15 ], but what you get in practice will very much depend on individual circumstances, as David VK3AUU has described.

What the heck. Erecting antenna is like other sorts of erection (flag poles, windmills . . .) - just get it up and then see what happens.

73, Roger Harrison VK2ZRH

[VK4QB]

Yes Roger,
It's what you do with what you've got that matters.
Brian 4QB

[VK4ABW]

The angle of elevation varies from location to location and even changes with the time of year! yes, when it rains, your angle changes.

But, there are situations where some ground reflection can be an advantage. A single yagi with ground reflection can exhibit up to 6db more gain when doing EME That's why my EME system is on a crank up tower

Many years ago i used to believe that putting my beam about 3mtrs above the treeline was optimum.....but things change with time and experience. Comparing my 11el yagi's (1 at 95ft and 1 at 125ft) they are worlds apart. Even allowing for the extra feedline, the top antenna consistently outperforms the lower yagi all year round. And not just on the local stuff. Who would think that another 35ft at that height would be worth it

For suburbian situations my recommendation would be 1 yagi at 2 wavelengths and another at 3 wavelengths AGL. This is off course providing that no buildings or trees hinder at those heights.

NOTE: in 1990 after building my first long boom yagi at 60ft agl, i was amazed to realise that a large tree 1 block away changed my swr

Gary

[VK3AUU]

What Gary said about ground gain is very true.

Back in my early days on EME on 144 with a single yagi, I could not hear echos with 1500 watts (permit required) with the antenna pointing up into the sky, but I could easily hear 500 watts on the horizon or just above. LZ2US reckoned I sounded like an 8 yagi station on my moonset. It used to be interesting listening to the European stations all coming up out of the noise on their moonrise and then they faded down again when the moon got higher and they lost the ground gain.

[VK4WDM]

During the last SS cycle Gary VK4ABW and I were about 18k apart. He had a 9 el yagi at about 100ft (Gary correct me if I am wrong) and I had a 7 el at 60ft. Most of the dx ended up in both of our QTHs.

What was very noticable was that Gary started working the Europeans about 30 to 45 mins, and sometimes as much as 1 hr before I did. Once the the band really opened up I could work most of what he could albeit a few S points down.

On the USA path Gary could work stns that I could not hear at all and that cannot be explained on antenna gain alone.

The only conclusion one can come to is that "more height the better."

Having said all that, I certainly worked a good deal of long-haul Dx with several hundred Eu contacts, and others into Central Asia, Central America, West Coast USA and long-path to South America, and West Africa heard but not worked. So an antenna at a modest height will work ok.

A lot of its comes down to a well set up station on both receive and transmit, the skills of the operator, the use of such aids as Spectran or Digipan, and a good system for monitoring beacons.

My plans for the coming SS cycle include an improved yagi (maybe 9el) at the same height, and very importantly, getting my CW back up to acceptable - that's a major mistake I made last time. CW is absolutely essential for the 6m dxer. It is going to be a major hurdle though as I have a progressive high-frequency hearing loss that makes copying CW very difficult. I hope that some of the newer computer programs may be able to provide some sort of backup for the computer that is between my ears.

I am also going to install a good system for monitoring beacons 24/7 with sound activated recording, and an alert alarm on 50.110 similar to that used in maritime radio rooms to wake me me if an opening occurs in the middle of the night (have to find a way to make it XYL friendly or I might be sleeping in the shack (or dog house! ).

73

Wayne

[VK4APG]

Last cycle I had a five element beam at 45ft and lived 1717kms south of Gary. Had an opening to Eu for every ten enjoyed by Townsville stations. Perhaps the critical height involved is distance from the south pole?