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Moxon for 11 meters

Mike,
Since you are always trying to help others as well..
So here goes:

Attached a 3el with a very large metal roof ..
(just to be sure of worse caste scenario)
The antenna is 5 meters above it.

In this case it is actually "helping" a litlle bit :)

Of course there are situations where a house/roof etc will have worse behavior
But overall...you can see the take off angle isnt influenced by the house.

So it is fair to say:
...you can model with the heigth provided above ground instead of above the house.
With the restrictions i posted in earlier.

I hope this is helpfull...

Kind regards,

Henry
 

Attachments

  • sp5it.pdf
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@ Bow,

Attached a plot of the groundplane at 5,2 meters....(primairy)
inserted the moxon at 5,2 meters.
and inserted a moxon at 12 meters.

As you can see, it still is worth the effort.
And as we go higher we see that main lob going down.
Making it a better "DX" antenna.

heigth = migth.

hope it is of use,

Kind regards,

H.
 

Attachments

  • bow.pdf
    94.7 KB · Views: 37
Bow said:
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...
Click to expand...

Really it will. They work well at half a wavelength high or more which 17ft roughly is. I used one on 10m in the 2012 CQ-WW-DX SSB contest. It was just a few feet higher. With 100W I worked 502 contacts in 91 countries in 31 ITU zones in just 16 hrs setting a new country record for England.

CQ WW Contest - Searchable Score Database

Here's the Moxon. The height of the building the pole is bolted to is 8ft.

 
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sp5it said:
Bow, you can try to add second vertical an try Christman phasing. Dunno how it will improve on 27MHz, on 7MHz works great.
Click to expand...


Funny you mention that... I actually considered building a second 1/4 Wave Ground Plane and doing a Phased Array, aimed for East/West direction...
But looking through the old Antenna books, it didn't seem like the gain (~3db?) or Nulls would be enough to make it worth the effort...

Again, I can not find much solid information on 10/11 Meter phased Arrays with modeling. I understand staying Vertical might help my Take-off angle over Horizontal at the same mounting height...
 
Henry HPSD said:
@ Bow,

Attached a plot of the groundplane at 5,2 meters....(primairy)
inserted the moxon at 5,2 meters.
and inserted a moxon at 12 meters.

As you can see, it still is worth the effort.
And as we go higher we see that main lob going down.
Making it a better "DX" antenna.

heigth = migth.

hope it is of use,

Kind regards,

H.
Click to expand...

Thank you Henry. That is a very interesting thing you did on the Model.

It shows "Good", "Better", "Much Better" as far as signals go. it does show that a Moxon, even at 18 feet AGL would be worth the effort.

Taking into account what Mike was talking, with 2 phased Verticals, would it be possible to model and compare 2 - 1/4 Wave Groundplane Anteannas, mounted at 18 feet, and phased for an End Fire Array to a Moxon at the same height?
 
M0GVZ said:
Really it will. They work well at half a wavelength high or more which 17ft roughly is. I used one on 10m in the 2012 CQ-WW-DX SSB contest. It was just a few feet higher. With 100W I worked 502 contacts in 91 countries in 31 ITU zones in just 16 hrs setting a new country record for England.

CQ WW Contest - Searchable Score Database

Here's the Moxon. The height of the building the pole is bolted to is 8ft.
Click to expand...

Well guys here is an Eznec model I did of Homer's 11 meter Moxon at 36' feet. This is not to suggest that these models will show the exact result Bow and M0GVZ might experience with their physical antennas, but these models might give us a clue for the effects and the differences due to a simple change in height. I lowered the model to 17' feet in order that Bow might get some idea of the change in performance he could experience.

You will notice a little difference in the maximum gain of 11.39 dbi at 14* degrees on the 36' foot mast vs. 10.26 dbi at 28* degrees for the 17' foot mast, a really big change in angle.

For an additional comparison, I added a pattern of the 17' foot model with the angle cursor set at 14* degrees above the horizon. This compares the maximum gain and angle of the 36' foot model to the 17' model at the same 14* degree angle.

Good luck Bow.

View attachment Moxon for Bow.pdf
 
M0GVZ said:
Really it will. They work well at half a wavelength high or more which 17ft roughly is. I used one on 10m in the 2012 CQ-WW-DX SSB contest. It was just a few feet higher. With 100W I worked 502 contacts in 91 countries in 31 ITU zones in just 16 hrs setting a new country record for England.

CQ WW Contest - Searchable Score Database

Here's the Moxon. The height of the building the pole is bolted to is 8ft.
Click to expand...

That is a hell of a testamonial! Thanks for the vote of confidance
 
Marconi said:
Well guys here is an Eznec model I did of Homer's 11 meter Moxon at 36' feet. This is not to suggest that these models will show the exact result Bow and M0GVZ might experience with their physical antennas, but these models might give us a clue for the effects and the differences due to a simple change in height. I lowered the model to 17' feet in order that Bow might get some idea of the change in performance he could experience.

You will notice a little difference in the maximum gain of 11.39 dbi at 14* degrees on the 36' foot mast vs. 10.26 dbi at 28* degrees for the 17' foot mast, a really big change in angle.

For an additional comparison, I added a pattern of the 17' foot model with the angle cursor set at 14* degrees above the horizon. This compares the maximum gain and angle of the 36' foot model to the 17' model at the same 14* degree angle.

Good luck Bow.

View attachment 13170
Click to expand...

Wow, thanks Marconi.

I've got to find some time to learn that antenna modeling software....
 
sp5it said:
Bow, you can try to add second vertical an try Christman phasing. Dunno how it will improve on 27MHz, on 7MHz works great.
Click to expand...

AHH the christman forced current phasing method, it does indeed work on 7mhz.
 
Marconi said:
You will notice a little difference in the maximum gain of 11.39 dbi at 14* degrees on the 36' foot mast vs. 10.26 dbi at 28* degrees for the 17' foot mast, a really big change in angle.

For an additional comparison, I added a pattern of the 17' foot model with the angle cursor set at 14* degrees above the horizon. This compares the maximum gain and angle of the 36' foot model to the 17' model at the same 14* degree angle.

Good luck Bow.

View attachment 13170
Click to expand...

The important bit about those graphs is the 10-15 degree ToA angle as statistically that's the one thats going to be around the most common angle of arrival for signals up to around 7000 miles. Even at 17' you have 5dBi of gain at 10 degrees take off and whilst that is 5dBi less than it is at 36' it'll still give you more gain over a vertical.

However what is more important than absolute forward gain is the ability to null out signals that you don't want. If you're trying to talk to someone in Europe the problem you have with a vertical is that you get to hear everyone in the USA which makes working Europe a lot harder. Because of the nature of the antenna, signals coming in from the rear and the sides are massively attenuated making it easier to hear what you're actually wanting to work.

So whilst 36' would be great if you can get it up there, its still worth putting up at 17'.
 
Bow said:
So my next question:

How do you tune the Moxon for the desired frequency?

Do you shorten the "tails" on the Driven?
Increase the gap between the elements?
Adjust the width of the long side?

Thanks
Click to expand...

A good question Bow. I don't have a good or specific answer for how to tune to a particular frequency on a Moxon, but I would guess a lot depends on the material used and if you provided for adjusting the elements or not.

The Eznec model of Homer's antenna that I posted above shows an almost perfect match at 26.955 mhz. I think I remember naming that model with word "New" in the model name, because Homer, at some point, made a change in the dimensions he used or he happened to build a new antenna...maybe using a different Moxon calculator.

When I fix his old model with the new dimensions I can remember being a little surprised that I had to change frequency to get the good match. When I did that to my model the frequency was much lower...near Channel 1.

I don't recall if I we ever talked to about that...but I think he would have wanted to set his resonance higher rather than lower in frequency. I also think Homer used one of the Internet Moxon calculators to get his dimensions.

What is you source for your Moxon dimensions?
 
Bow said:
I'm using the MoxGen software.

Center Freq: 27.555
Material: 0.5 in. Copper pipe

I figure 4 sticks of copper will give me plenty to work with, 90 Copper elbows for the corners, PVC for the spacers.
Click to expand...

Homer will be a good source for info on what he thinks about this software. I would guess however, that he used the dimensions he generated for his Moxon at his frequency of choice. That is why I was surprised when I saw the model I made resonating down at channel 1 for CB. Homer might have a better recollection of what happened back then...if we had any further discussion about the model.

This is also not to say that I believe the models I make are absolutely Gospel and are providing perfect results. In fact I hear folks that do models and then build the physical model according to the software results...discover the resonance can be off a bit from the software results.

So, modeling may often be close, but it ain't perfect and it cannot account for obstructions, soil conditions, and terrain at your location.

I just hope Homer did not suffer the storms that went thru parts of Arkansas recently. If not, he may just be very busy this time of year.
 

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