Moxon for 11 meters

[Bow]

Howdy All,

I have a limited space to put up my antenna, due to "Cosmetic Reasons"..

Right now, I am running a homebrew Ground plane: 102" Stainless Whip with 4 radials. It has been doing pretty well in the DX with 100 watts, but I'm getting a bit tired of being the hard to hear guy...

I am looking to build a Moxon. After reading a lot of articles/posts/etc on the internet, it seems to be the best bang in the smallest package.

I want to build one out of 1/2 copper pipe for strength, it will be about 5ft above my flat, composite roof and about 17 feet off the ground.

I want to go with copper because: I can get it local, the AZ sun will bake PVC in no time, and we get so serious wind out here in the desert.

According to the MoxGen Calculator, I will need about 34.5 feet of 1/2" copper pipe, but my question is, what should I use for the "Boom" to mount it to the mast, and the seperators between the elements?

I have not figured out the Antenna modeling software yet, so I am not total sure what to expect at this height. Any ideas what the bandwidth would be if it is centered at 27.555 MHz?

Can anyone provide any information I maybe missing?

Thanks

 

[Henry HPSD]

Hello,

I would definitly go for a higher placed moxon.
horizontal antennas have additional ground gain, much more than verticals do.
horizontal antennas need heigth in order to get a low take off angle.

Your just on the point where horizontal antennas start to get bennefit above verticals for Dxing. Going higher would be your first goal.
Im not saying you wont be able to take skip, im saying it is benneficial to go higher.
(at least if your into talking skip).

Copper is heavy...
Isnt there a aluminium supplier somewhere ?

You could make it out of copperwire and a couple fishingrods.
I know you said it will break, and heavy winds...
But the antenna will only cost a couple bucks, who cares if it brakes.

For element seperators we use fiberglass rod. (not tube)
Cant remember how many moxon's we already made...but all are still up.

Typical bandwidth is in the order of 1,6 MHz (2:1)


Kind regards,

H.

 

[Bow]

Hello Henry,

Thank you for the reply. I was wondering if a directional antenna would be worth my effort at the hieght I have to work with, and it sounds like it may not be...

I was afraid of that...

I figure anything with directional properties would be an advantage over my 1/4 wave ground Plane Vertical at the same height

 

[sp5it]

Hello Henry,

Thank you for the reply. I was wondering if a directional antenna would be worth my effort at the hieght I have to work with, and it sounds like it may not be...

Delta loop does not need as much height as Yagi.
DELTA LOOP Antenna 26-30 MHz, 10m-11m
Mike

 

[Henry HPSD]

Hello..

In my opinion its still worth the effort, especially with the high sunspot numbers.
Though it is wise to invest in a bit more heigth, with horixontal antennas The difference is noticable..

Ill see if i can provide some plots for u.

Kind regards...

H

 

[Henry HPSD]

Ps mike...

What makes you think the delta loop doesnt need that heigth ,?

Kind regards.

H

 

[sp5it]

Just practice with antennas Henry.
3m over mounting place it have 11dBi forward gain and elevation angle 25 degrees. Not that bad for 2 element antenna.
2 element Yagi at the same height will have 60 degrees elevation angle which is pretty useless for DX.
Mike

 

[Henry HPSD]

Hello Mike,

Thank you for responding.

Ah, i think i know what you are getting at.

What you have done (probarbly) is measured the delta loop at its lowest point at took that for "3 meters"
The top heigth of the delta loop in your case will probarbly be something around 6 meters ?
The bottum heigth around 3 ?

Where the 2el yagi is situated at just 3 meters in your example.

Think we had a discussion going on about :
antenna feedpoint heigth, antenna current heigth and antenna top heigth...etc..there are differences of course.

The topic starter is referring to 17 feet, roughly 5.2 meters.

Without having it verified yet, i think you will find the difference become less, and when placed higher one can say "neglible".

Pehaps a vertical polarisation one the delta loop would evan provide a lower take off angle ? At 3 meters heigth...worth giving it a try.

If he really want to take advantage of the heigth of an antenna system...
Perhaps we could recommend a 2el Hentenna, or a bi-square ?
Or maybe evan such a 2el jogunn thingy...would be something to try in antenna software.
We will have to find out what would be best..

No mather how we deal with the situation, the end solution will be ....placing the antenna higher of course.

But tnx, again

Kind regards,

H.

 

[Bow]

Thank you for the replies gents.

Henry,

If you could do some plots, that would be great. I would like to use 1/2in M copper because it is durable, will not wiegh too much, and can be found locally. Every thing I need should be less that $50. (10' of M 1/2" copper pipe is roughly $10 locally)

Mike,
I have looked at a Delta loop, but I have a height restriction. A horizontial moxon would be quite low profile compared to a Vertical Loop/Delta antenna.

I may be able to mount it as high as 20 feet AGL before visability becomes an issue, roughtly 1/2 a wavelength on 11 meters, but I said 17 feet as a more probably number, and the extra 3 feet probably will not gain much.

Thank you gents for your inputs, I have never built a directional antenna, several fan dipoles, loaded dipoles, and verticals, but this is my first adventure into a directional.

 

[sp5it]

Height above the roof is important in that case, not over the ground.
So, in every simulation height of your antenna will be 5 feet not 17-20.
Mike

 

[Henry HPSD]

Hello Mike,

Woudnt you agree with me that the far field of the antenna is made up to about 20 wavelengths away from the antenna ?
And yes, of course this also includes the proximity of the house.

Of course i dont know how "big" his house is, but i doubt if its 1200 feet in diameter and
believe his house is probarbly in percentage relative small.

Now, im not saying it wont have any negative effect....(especially when there is snow/rain etc) but i am saying...i do believe it is not as important as you think it is.
and that the ground around his house is important.

Kind regards,

H.

 

[sp5it]

Henry, practice shows it that building and roof is not netral when it is located below antenna. Height depends on frequency of course.

Simple example.
My friend have 8 element Yagi for 10m. When antenna is in specific direction 1/3 of it is over a building which is 8m below. In that direction it is easily noticable that resonance and SWR is changing.
Mike

 

[Bow]

Again, thank you for the help gents.

Right now, with only a 1/4 Wave GP on the same roof, I am just looking to build something that will get out better than what I have... and I believe "more Power" is not the answer, so the next logical thing to look at is the radiator of the power I have at the moment...

 

[Henry HPSD]

Ah but mike..

Youre confusing two different things....swr is easily influenced in the near field....something different to the far field where the radiation pattern is made up.

Kind regards

H

 

[sp5it]

Henry, yoy have Eznec, make a simulation with and without building please. We'll see what will be a diffrence. With 3 element Yagi for 11m.
Mike