Interesting Antenna Height Question...

[45 North Florida]

Hello, I'm a new member and this is my first post. My question/need of opinion is as follows:

I have a 4 element Sirio mounted at 50'. Would I benefit any lowering it down to 36ish feet to get it to the height or 1 wavelength, or just leave it at 50' and let it ride there? It would be easy to lower it, but just checking.

The tower is up against my house with a metal roof, and currently the boom is right at 36' above the roof.

Any opinions or suggestions are much appreciated!


45 North-Florida

 

[sp5it]

As high over metal roof as you can. 2 wavelength best.
Non conductive is a different story.
Mike

 

[45 North Florida]

Just what I was thinking myself Mike, thanks. So the myth of landing exactly on the first wavelength is not necessarily better than just above it, if I can't quite make it to the second?

 

[sp5it]

Conductive objects, especially big ones affect antenna, usually bad way. Vertical, horizontal. Skew antenna pattern, affect gain, resonance freq and so on.
2 λ is considered as safe distance.
M

 

[BC Coyote]

For skip work there is no point in going higher than 36 feet unless you have objects such as buildings that the antenna needs to "see" over the top of.

For local, the higher the better! Raising an antenna 20 feet will be roughly equivalent to doubling your power.

So to answer your question; lowering from 50 to 36 feet will make zero difference for skip, but will cut local signals by about 3dB.

 

[45 North Florida]

Thanks guys these replies make perfect sense and clears a lot up!

 

[Henry HPSD]

You wont benefit anything by lowering the antenna, most likley the opposite is true.
There is no "magical" optimal height for horizontal Yagi antennas.

I have a different opinion then BC Coyote...but maybe it depends a bit on your personal situation, the ground around your antenna certainly has influence.

For me ( and in most cases)
It can make a difference to go higher then 36 feet, especcially for that "long haul" skip work.
As going higer will lower your TOA (take off angle). With that said...you most certainly can work the entire world @ 36 feet..no doubt about that.
I used to have a stack at at say 70 and 35 feet.
The top antenna always had the edge compared to the bottom one when it came down to "real" DX. In other situations (E-skip) the results could vary.

How high should i place my beam ? – 19DX348 CB Antennas

cb-antennas.com

Kind regards, Henry

 

[45 North Florida]

Very valuable info, as well as the link that you attached Henry, thank you!

 

[Mustang 131]

I've run Yagi's at 6' off the ground to 120' off the ground. In my stupid uneducated experience....anything above 36' is good enough.
Running a quad at 50' now..seems good. But it also worked just fine a 12'.

 

[sp5it]

Ground distance influence on quad is totally different than for a Yagi.

 

[DXman]

For the last 49 yrs now, I have run a 5 element horizontal beam at 36' (11 meters), my altitude is 24' (7.32 meters) above sea level and the only thing that I would do different would be to go higher.
From what I have understood, is that going higher can also give more forward gain (to a certain point).

I have spoken with Henry HSPD in the past on the radio, and he has some great knowledge about antenna working. He even ran my Maco 5 element though his modeling program to get the resonating freq. where I wanted it.

I don't run anything but the 100 watts that the radio puts out, a good tuned antenna at a good height is the secret.

 

[Crawdad]

From what I have understood, is that going higher can also give more forward gain (to a certain point).

The gain a Yagi can create is not a function of height above ground but by the amount of director elements and element spacing. The largest affect of height above ground is the raising or lowering of the take-off angle of the strongest lobe of the radiation pattern. Depending of course on the earth or objects beneath the antenna and their conductivity.

7 3

 

[AudioShockwav]

Very valuable info, as well as the link that you attached Henry, thank you!

Henry has a awesome website full of good information, I keep it in my bookmarks.

73
Jeff

 

[Captain Kilowatt]

The gain a Yagi can create is not a function of height above ground but by the amount of director elements and element spacing. The largest affect of height above ground is the raising or lowering of the take-off angle of the strongest lobe of the radiation pattern. Depending of course on the earth or objects beneath the antenna and their conductivity.

7 3

DX Man is probably talking about the extra 5 to 8 dB gain a horizontal antenna can achieve from what is called ground reflection gain. The take-off angle changes with height. The angle that the signal strikes the ground and is reflected, combines with the incident wave signal and actually adds gain at a distant point. This can be used to optimize a signal at a specific target area.

 

[Crawdad]

DX Man is probably talking about the extra 5 to 8 dB gain a horizontal antenna can achieve from what is called ground reflection gain. The take-off angle changes with height. The angle that the signal strikes the ground and is reflected, combines with the incident wave signal and actually adds gain at a distant point. This can be used to optimize a signal at a specific target area.

Thought that's what I said...........