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I tend to agree with you this is the best way to help minimize CMC.

Bob, I could be wrong, but I think this could be meaningful for consideration.

I'm sure you've seen and read the article below, written by W8JI. You might also recall our discussion back in 2010, where I proposed an idea base on this article. That idea suggested that maybe we could mitigate CMC on our antenna mast and feed line...simply by using some particularly suitable mast height and feed line length to the ground if we could determine what that length was.

The other day I posted a comment suggesting my Eznec5 modeling efforts indicated that the magnitude of CM currents seemed to vary along the mast in a sinuous curve rather than linear and, among other things, that was due to changes in height. I also noted that modeling indicated this at very small differences in height. This is not all there is to the issue, but IMO the following pdf file is in response to your comments above. I also think this might tend to agrees with what W8JI suggested below.

I used a portion of another modeling project where I compared a full 1/4 wave radiator vs. 1/4 wave that was shortened with a large Top Hat. In this case I selected the model that was a 1/4 wave resonant ground plan at 40' feet to support my point. I adjusted this model to 17' - 19' feet for your consideration. The purpose for my choosing these models was to see the affects of height on matching as well, and using a resonant antenna that matched to some numbers that we might expect, thinking that would be helpful in understanding.

Take note of the current magnitudes indicated in red at different heights, and the affects this has on the patterns. I was really amazed at what 19' & 20' feet showed. Sorry I forgot to include 20' feet in the pdf, but it was the worst of all.

[ATTACH]5530[/ATTACH]

By the way Bob, I agree that laying the coax on the ground will help minimize CMC into the shack, but they will still radiate from the feed line as it hangs from the antenna, and the feed line can still remain a problem.

<blockquote data-quote="Marconi" data-source="post: 311692" data-attributes="member: 903">I tend to agree with you this is the best way to help minimize CMC.&nbsp;&nbsp;Bob, I could be wrong, but I think this could be meaningful for consideration.&nbsp;I&#039;m sure you&#039;ve seen and read the article below, written by W8JI. You might also recall our discussion back in 2010, where I proposed an idea base on this article. That idea suggested that maybe we could mitigate CMC on our antenna mast and feed line...simply by using some particularly suitable mast height and feed line length to the ground if we could determine what that length was.&nbsp;The other day I posted a comment suggesting my Eznec5 modeling efforts indicated that the magnitude of CM currents seemed to vary along the mast in a sinuous curve rather than linear and, among other things, that was due to changes in height. I also noted that modeling indicated this at very small differences in height. This is not all there is to the issue, but IMO the following pdf file is in response to your comments above. I also think this might tend to agrees with what W8JI suggested below. &nbsp;I used a portion of another modeling project where I compared a full 1/4 wave radiator vs. 1/4 wave that was shortened with a large Top Hat. In this case I selected the model that was a 1/4 wave resonant ground plan at 40&#039; feet to support my point. I adjusted this model to 17&#039; - 19&#039; feet for your consideration. The purpose for my choosing these models was to see the affects of height on matching as well, and using a resonant antenna that matched to some numbers that we might expect, thinking that would be helpful in understanding. &nbsp;&nbsp;Take note of the current magnitudes indicated in red at different heights, and the affects this has on the patterns. I was really amazed at what 19&#039; &amp; 20&#039; feet showed. Sorry I forgot to include 20&#039; feet in the pdf, but it was the worst of all.&nbsp;[ATTACH]5530[/ATTACH]&nbsp;By the way Bob, I agree that laying the coax on the ground will help minimize CMC into the shack, but they will still radiate from the feed line as it hangs from the antenna, and the feed line can still remain a problem.</blockquote>

[QUOTE="Marconi, post: 311692, member: 903"] I tend to agree with you this is the best way to help minimize CMC. Bob, I could be wrong, but I think this could be meaningful for consideration. I'm sure you've seen and read the article below, written by W8JI. You might also recall our discussion back in 2010, where I proposed an idea base on this article. That idea suggested that maybe we could mitigate CMC on our antenna mast and feed line...simply by using some particularly suitable mast height and feed line length to the ground if we could determine what that length was. The other day I posted a comment suggesting my Eznec5 modeling efforts indicated that the magnitude of CM currents seemed to vary along the mast in a sinuous curve rather than linear and, among other things, that was due to changes in height. I also noted that modeling indicated this at very small differences in height. This is not all there is to the issue, but IMO the following pdf file is in response to your comments above. I also think this might tend to agrees with what W8JI suggested below. I used a portion of another modeling project where I compared a full 1/4 wave radiator vs. 1/4 wave that was shortened with a large Top Hat. In this case I selected the model that was a 1/4 wave resonant ground plan at 40' feet to support my point. I adjusted this model to 17' - 19' feet for your consideration. The purpose for my choosing these models was to see the affects of height on matching as well, and using a resonant antenna that matched to some numbers that we might expect, thinking that would be helpful in understanding. [SIZE=6][/SIZE] Take note of the current magnitudes indicated in red at different heights, and the affects this has on the patterns. I was really amazed at what 19' & 20' feet showed. Sorry I forgot to include 20' feet in the pdf, but it was the worst of all. [ATTACH]5530.vB[/ATTACH] By the way Bob, I agree that laying the coax on the ground will help minimize CMC into the shack, but they will still radiate from the feed line as it hangs from the antenna, and the feed line can still remain a problem. [/QUOTE]

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