What does Exnec say about a couple of Moxon Calculators?

[HomerBB]

BI found the F/B to be remarkable on my Moxons.
How did the indoor wire do?
I put a fixed wire Moxon in the attic and hardly used it. Not so good being spoiled by outdoor antennas.
I made and used at least two 2el yagis, ref/driven. They worked well. My sense of things was the moxons were better.

 

[711]

BI found the F/B to be remarkable on my Moxons.
How did the indoor wire do?
I put a fixed wire Moxon in the attic and hardly used it. Not so good being spoiled by outdoor antennas.
I made and used at least two 2el yagis, ref/driven. They worked well. My sense of things was the moxons were better.

I climbed into the attic of my garage and mounted both a dipole and Moxon up there. They both didn’t tune very well. My ceiling was 9’ and shot skip from Hawaii to Christmas Island with just a 2950 . As with both Moxons , they didn’t do very well locally but was more suited towards skip.

 

[HomerBB]

I prefer the tubing Moxon. It tunes easier, and maintains the tune in high wind.

 

[Marconi]

BJ and Homer, I think the difference that BJ suggested about Bill Orr's book is considering the difference between results from a Free Space model, with all the losses removed, and a Real Earth model, with losses included in the model.

There is a bit of difference between modeling technology 44 years ago and today, but there is very little difference in the results.

I included two images of the end dimensions so we can calculate the Moxon spacing in this case. Add the mumbers to the 5.86" end gap and you get 57.25" inches for the spacing.

57.25 / 433.849 Eznec wavelength at 27.205 MHz and we see a compromise ratio of 0.13 wavelength spacing. IMO this is probably done to maintain the nice bandwidth to gain values with the caluclators.

The overlays at the end show the pattern differences.

 

[Marconi]

I climbed into the attic of my garage and mounted both a dipole and Moxon up there. They both didn’t tune very well. My ceiling was 9’ and shot skip from Hawaii to Christmas Island with just a 2950 . As with both Moxons , they didn’t do very well locally but was more suited towards skip.

Good observations 711, as you likely know that is probably due to the Moxon, in these examples, being horizontal and most local CB bring vertical.

Thank you for your Service Brother.

 

[711]

Good observations 711, as you likely know that is probably due to the Moxon, in these examples, being horizontal and most local CB bring vertical.

Thank you for your Service Brother.

My amp builder saw my wire Moxon I had up in the back yard at a stateside house I had and he put one up on my measurements and made it rotatable between horizontal and vertical, with a little higher reflect in the vertical plane , I suspect due to the tower , he worked locals very well also.

 

[Marconi]

My amp builder saw my wire Moxon I had up in the back yard at a stateside house I had and he put one up on my measurements and made it rotatable between horizontal and vertical, with a little higher reflect in the vertical plane , I suspect due to the tower , he worked locals very well also.

711, I would sure like to see this antenna, if you have any pictures or a drawing? I would like to model the idea.

 

[711]

711, I would sure like to see this antenna, if you have any pictures or a drawing? I would like to model the idea.

I don’t have any pictures, some wind took it out and he went with a super scanner

 

[wd8dsb]

Today I solved the mystery about the online Moxon calculators such as KG4ZOW and W4/VP9KF that return dimensions that do not model well on 4NEC2, whereas the program MoxGen generates dimensions that model correctly in 4NEC2. I found the problem to be an error in one line of the source code that KG4ZOW said he uses where there should have been a multiplication function but a division function was used instead. I am able to duplicate the incorrect values that these online programs generate by using the same mistake that they used. I have reported this error to KG4ZOW as well as W4/VP9KF since they both generate similar values which are not correct based on the work done by L. B. Cebik (W4RNL) who created the formulas being used.

 

[Marconi]

Thank for the new information wd8dsb. The problem sounds like some silly things I sometimes do.

Sometime back, i did some Moxon models using several calculators on the Internet. I found some difference in results among several, and my thought was to try and alert a few folks on this forum that had an interest in the Moxon design.

I used modeling with several of these tools and found some were lacking in results.

I could never have done the work you did in this case, but I think maybe a few might understand your explanation for what you found much better than I could ever manage using modeling to demonstrate the problem.

Thanks for the help.

 

[wd8dsb]

Hi Marconi,

The correct formulas were generated by W4RNL and his Basic program can be found at the website with a URL of http://on5au.be/content/a10/moxon/moxgen.html. The problem I found that causes values that don't model well is as follows: The error in the KG4ZOW online calculator source code reads: $d1 = 0.4342945 / log ( $dw )
but the constant 0.4342945 should have been multiplied by log ($dw) not divided by it.

Here is a copy of the correct code from the W4RNL basic program: D1=.4342945*LOG(DW)

I was able to create my own Moxon calculator spreadsheet using the W4RNL basic program and my spreadsheet generates values exactly as the downloadable program called MoxGen, and these values model just fine in 4NEC2. If I change my spreadsheet to include the error in the KG4ZOW program mentioned above, my spreadsheet then generates values like the KG4ZOW online calculator which model poorly. Simple but critical error for those building Moxon antennas. Since finding the error I have not heard back from KG4ZOW or W4/VP9KF but hopefully they will eventually respond and correct their online calculators or remove them from the internet.

P.S. the LOG function in the above mentioned code is a natural log function, not a base 10 Log function for those wanting to create their own Moxon spreadsheet.

Take care,
Don (wd8dsb)

 

[Marconi]

Thanks Don for the further explanation.

I have no idea how many folks suffered the consequences in trying to get dimensions and actually build a Moxon antenna using such tools...only to fail in frustration and not knowing why.

In my work with modeling I tried to suggest something was wrong with some of the calculators, and that based purely on my Eznec models.

That said, Eznec and possibly Modeling in general have received such bad reviews on these radio forums...that the idea of modeling and its results are pretty much a vain effort. Over time numerous operators that could model, to some degree or another and some just starting out using such tools, have just come and gone. I regret that.

Again, your description of these issues, and you're informing the members of some problems with the code in some Moxon generators...is pretty clear and makes very plausible sense for me. We need more members that have skills.

Thanks.

 

[wd8dsb]

Marconi,

I forgot to say that the proof is in the pudding. This past week I built a Moxon for 135 MHz and one for 146 MHz. I tested both antennas and their SWR plots as well as front to back ratio fall in line with what I expected based on their 4NEC2 models. I use 135 MHz for tracking down power line interference, and you can see a short video I loaded onto youtube yesterday comparing my 135 MHz Moxon with my 135 MHz 4 element Yagi at a known bad power pole. I'm impressed with the front to back ratio of the Moxon which is very useful for direction finding and it's much smaller than my 4 element Yagi.

Here is a link to my youtube video for those interested:

Great job to you trying to encourage folks to model.
Don (wd8dsb)

 

[Marconi]

Thanks Don. Very good video and impressive demonstration of both antennas in action.

I have no doubt that several members, here in the Antenna section, will get a kick at your work in producing these comparisons videos.

At the bottom of my posts, in the signature area, is a link to a list where I once upon a time made some "corny" videos of what I was doing trying to test my ideas on comparing a bunch of vertical monopole CB antennas I had accumulated.

In looking back, I don't know if I just had a zeal for comparing antennas and wondering how they worked, that is the way it all started for me. Or, if it was my being able to understand and produce little videos to help demonstrate what I was trying to do with the new technology. And baring to all the many mistakes I made in the process back in a time that seems like - way back to a bunch of like minded guys on this forum.

Fact is I'm still discussing related ideas about this very topic, comparing antenna performance with some of my favorite folks in the first thread in the "Sticky Threads" section at the top of the WWDX, CB Antennas at the top of the front page.

Don, please come join us. I need some help. Some of these guys are also heavy into "fox hunting," I think.............if I recall correctly.

I'm 84 and these young guys have the advantage over me sometimes, while I'm trying to remember how to spell "I" or is it "eye."

Marconi - Grampa on the air.

 

[Marconi]

Don, here is my Big bad Boy