I believe he said he arrived at this ratio by watching the reaction of the models at varying ratios while he tried to squeeze the best gain and match at various elevations
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Base Open Sleeve EFD
- Thread starter Marconi
- Start date
i just read Eddies original post where he set it to 3:1 as in the article and got a poor match, i can't explain that when the guy measured low vswr over the whole band.
putting the sleeve around the radiator electrically shortens it so it needs lengthening to restore resonance,
shortening it so there is significantly less than 1/2wave of radiator above the sleeve makes no sense to me, i would like to hear the explanation,
i know Cebik did it with none standard j-poles.
putting the sleeve around the radiator electrically shortens it so it needs lengthening to restore resonance,
shortening it so there is significantly less than 1/2wave of radiator above the sleeve makes no sense to me, i would like to hear the explanation,
i know Cebik did it with none standard j-poles.
Bob, in the blue hilite' above I tried to explain that I was also puzzled why my model reported so far off. Homer got my meaning. Do you remember the Vortex and the black and white pills?
I don't know the why, but I did the model over and it is still bad.This is why I won't be doing the model at 11 meter...until I understand exactly what is going on with the scaling feature. I been informed that it is a sin to ever get surprised in this business. But, I just follow my nose and what I can see in my minds eye, and for sure if I'm working on an article for information from the Internet.
When I use to build antennas around here with wire and wood...I think they were all failures. I might question a claim or two after that experience and for sure if the info comes from the Internet...the biggest lying tool known to man.
DB, do you have any scaling tricks? hehe!
Thanks Homer.
There are two model below plus one for the article out of the ARRL 19th Edition page 7-19 to 7-20.
I won't comment except to say I made notes that may help. I will make some models that hopefully will show the blow by blow when using the scaling feature.
Bob, this is what I started with. The fun and trouble had not started yet...but as I tried to say above...this model surprised me at every turn.
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Are you scaling the diameter as well?
I haven't done any scaling myself, haven't needed to.
Outside of modeling, when someone gives formulas for the lengths of various antennas, those formulas only work when so close to the original intended length of the antenna, although that is more because of the element diameter not changing along with the lengths of the elements, if you are allowing the diameter to change with everything else you should at least have a much wider range of adjustment.
I'll play with it this afternoon/evening when I get a chance.
The DB
Bob, the Skeleton Sleeve model is all better now. I have not done anything to directly control the AGT so far. The Fee Space model shows the model is a little out of range for an acceptable AGT. So, I'm using the Eznec AGT correction factor math to show us the corrected gain results.
See my notes to for dimensions and the math I used to get the resulting ratios I ended up with. I kept the wire diameter about the same as the 146 MHz model used.
I will try later to see if I can slowly make the diameter larger without crashing the model.
DB, I did not mess with the wire dimensions. I used segment count to hone in on this one. This way also allows me to use far less segment than I might choose otherwise.
It left me lacking in total control over the AG, but the match got really good and I figure the guys will like to see that from this SS model. I think this also prevented me from getting way off on the 3:1 ratio in the article.
I think now I can effectively consider other ratios and see predictable results...like the article is suggesting, and Bob has talked about, maybe 2 and >3.2.
This way I also don't have change the specs wire diameter or need to use the single segment wire for the source location. I can keep the model to specs just using the AG correction factor. This method might be more limited however.
Steve, this is the way I started doing this stuff back when I use to talk to you about doing Free Space models first...as a starting point.
See my notes to for dimensions and the math I used to get the resulting ratios I ended up with. I kept the wire diameter about the same as the 146 MHz model used.
I will try later to see if I can slowly make the diameter larger without crashing the model.
DB, I did not mess with the wire dimensions. I used segment count to hone in on this one. This way also allows me to use far less segment than I might choose otherwise.
It left me lacking in total control over the AG, but the match got really good and I figure the guys will like to see that from this SS model. I think this also prevented me from getting way off on the 3:1 ratio in the article.
I think now I can effectively consider other ratios and see predictable results...like the article is suggesting, and Bob has talked about, maybe 2 and >3.2.
This way I also don't have change the specs wire diameter or need to use the single segment wire for the source location. I can keep the model to specs just using the AG correction factor. This method might be more limited however.
Steve, this is the way I started doing this stuff back when I use to talk to you about doing Free Space models first...as a starting point.
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If I'm scaling a close by frequency I don't mind all the dimensions changing...but going from 2 meters to 11 will make the parts much larger in diameter and length...probably not so good.
I set the wires to wavelength, scaled the model, and then set the model back to inches or mm. A little trick I learned in the orient. hehe!
I'm working on setting the wires up so I can use the "group change feature" in Eznec...to change the wires pretty much all at once or close. If I figure it out and get it right...I'll send Homer the tool kit algorithm.
If Homer builds one these boggers...he will likely need to make some very difficult changes to the spacing in addition to the wire lengths to get the antenna to talk around corners and such.
It remains notable to me how the Nv4k continues to exhibit more gain than both the J pole and the SS. Either of these two antennas should have the same advantage of the current maxima being higher above the mounting point due to their lengths over all of 3/4^.
Seems to suggest more is going on with the Nv4k than meets the eye. Although the comparison of antennas of somewhat comparative structure proving the Nv4k is no more than a dressed up j pole should have been the results, so far, the modeling seems to support a different verdict.
The Nv4k continues to be better (than the "other" j-pole types). J-poles are not keeping up.
Seems to suggest more is going on with the Nv4k than meets the eye. Although the comparison of antennas of somewhat comparative structure proving the Nv4k is no more than a dressed up j pole should have been the results, so far, the modeling seems to support a different verdict.
The Nv4k continues to be better (than the "other" j-pole types). J-poles are not keeping up.
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Sorry I haven't gotten on this yet. A lot of things all happened at once and I'm still working on some of them. When it rains it pours. I haven't forgotten, I've just been busy. I'll get to it when I can, perhaps tomorrow, but with how my weekend ended up I don't want to make any promises.
The DB
Homer, a long time ago I told Bob something similar to your words above. I think it was before I was able to model the antenna to specs. I didn't have to depend on others for the dimensions, I own an S4, and I could test it in the real world too. So, later I was able to model it without grappling for good dimensions.
I wasn't totally wrong in my comment to Bob and neither are you in your comment above. But, everything I did with my S4 suggested to me it was closer to acting like a 1/2 wave monopole than a non-apparent colinear nor was it a mystery that could not be explained easily. As I recall, it was also said by an expert in antenna modeling that modeling would be difficult to impossible for such a design. Henry concluded differently from your idea in his report...see highlighted section in attached PDF file below.
This said, back in those days it was also quite common to hear the new 5/8 wave high gain antennas referred to as a colinear, probably because they had 2 current maximums in the current distribution.
So hearing all the CBBS of the times, I concluded that my S4 just happened to raise the maximum current lobe up higher than most other antennas that were also mounted on the same mount. Then after a while modeling with Eznec I was convinced the S4 was a very good antenna, and since most operators were likely limited to raising their antennas higher...the new longer antennas were probably a good deal for some that got the antenna installed correctly. I've heard plenty that complained too.
Later we heard well-informed folks (Elmers) adding a new wrinkle, saying if we compared two antennas and we don't get generally accepted results...then it is likely one of the antennas has a problem. And the story continues.
Homer, sometimes I'm guilty of the same thing...can't see the forest for the trees, or I'm wearing Rose colored glasses. These antennas are not that different. See the attached words by Henry HPSD on page #40, highlighted.
I think when Bob realized what Henry was going to report...he knew I was right all along. He even contacted me with the good news a few days before he posted his thread with the link to the article "The Avanti Sigma4."
The J-Pole has been around for a very long time and is woefully unappreciated, mostly due to a lack of good installation and/or construction skills.
More importantly, our own Bob85 has been sounding the woes and pit-falls for such problems that plague the J-Pole and other antennas...for years.
We know the J-Pole has a skewing issue, but you only see one side of the pattern...the pretty side that does not show the skewing. However, that is not the 1/2 of the antenna wave pattern that can produce the maximum gain at low angles.
If you check back I think you will find Bob and I were bantering about my showing him the antenna facing the X and Y axes. There you will see the difference that can make the J-Pole a player.
Don't take this personal Homer...IMO some consideration for the J-Pole is due. I have several 10-meter hams in my area that use a variety of J-Poles. Ever wonder why the S4 or the J-Pole design antenna are not listed in the Ham Catalogues? One is too expensive and one is too cheap.
I'm going to make a new thread for the J-Pole. Maybe something there will suggest why I consider the J-Pole a sleeper, plus I doubt many would ever notice its skewing flaw just operating on their radios...with typically flawed meters as is often said hereabouts.
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I hear you.
Yet, what I was referring to is your models with the three antennas overlayed. In each case it is your models, not my real world experience, to which I was commenting.
Some things I've learned over time.
Antenna aperture matters, but tip height really matters.
In your models all three are of equal aperture, and at the same tip height. My clear colored glasses see better over all patterns and slightly more gain from the Nv4k than the other two.
That's what I meant.
I do have a j pole on my 2m radio.
Seems to work well. I need to get it up higher to see how it compares to the homebrew 5/8 GP I was running. It did very well.
Yet, what I was referring to is your models with the three antennas overlayed. In each case it is your models, not my real world experience, to which I was commenting.
Some things I've learned over time.
Antenna aperture matters, but tip height really matters.
In your models all three are of equal aperture, and at the same tip height. My clear colored glasses see better over all patterns and slightly more gain from the Nv4k than the other two.
That's what I meant.
I do have a j pole on my 2m radio.
Seems to work well. I need to get it up higher to see how it compares to the homebrew 5/8 GP I was running. It did very well.
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Homer, I was all set to post my J-Pole idea in a new thread, but I noticed the model I had in line next was my End Fed prototype of the V4K without a radial hoop. I got it matched better today and showing a perfect AGT result = 1. The match is still of a bit, but it is a lot better than the previous 1.90 - 2.00> SWR earlier.
I will get to the heavy thinking part of your post for comment in a bit.
I have a real friend that lives about 40 minutes away from North of New Caney in some real woods...not like a few trees down the road at the park.
He and some of his buddies up in that area started using 2 meters and none of their various antennas work until...I bet Phillip if he used a J-Pole I had from Junior on Lake Marble Falls, Texas, them good-ole Boys could copy it...their problems could be over.
I use to talk to Junior of a morning on my Starduster when short skip was working. He is the one that builds copper antennas I've talked about here.
If the J-Pole worked like I though, then all those bootleggers/gin makers could really started working Tim's repeater near Plantersville, Texas big time. Tim is about 60 miles North of me...still in the woods where they don't ever get tourists...and them good ole country boys brag about it.
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I'de like to discuss two things about this discussion, starting with Henry's report. It may be just me, but when people refer to said report, I get the impression that they limit themselves to the parts of it that support the claims they once made (and still make), but not taking the report as a whole. The one thing that said report removed from the discussion was the collinear idea. That was it. Aside from this one thing that in todays sense is little more than a detail of history, it actually said that what both sides were saying was correct. It supported both Marconi's far field plots that never once showed 2 dBd gain figures, as well as Shockeave's real life measurements that showed 2 dBd gain over a dipole, and even suggested more was possible. No one seems to want to talk about what many before the report treated as a contradiction, everyone seems to be stuck on 'it said I was right', and they neglect to discuss other aspects of what the report actually said, and it said quite a bit. In addition, I can easily go back to when the report was released, their was more than one topic I discussed with Henry that no one payed any mind to, like said discussions were irrelevant. Seriously go back and read the thread and see for yourself. I find it sad that so much in that report is worthy of discussion, some pretty advanced stuff, and it seems to be ignored. Even when I brought part of it up, I got a like from Henry, but no one really said anything.
The other thing, when referring to the Vector antennas as being j-pole like. That is fine, I don't necessarily disagree, but that also comes with stipulations that are not being discussed. Its like a general statement is being treated as a fact, but the details that can disagree with said general statement are being ignored. As I recall, there were three different lengths for this antenna, ranging from 3/4 wavelengths to 7/8 wavelengths, as well as a few other recommended lengths thrown out as well. Can anyone honestly say that all of these lengths will act like a stub fed 1/2 wavelength antenna? I'm sorry, but to me at best that seems like a stretch, and my modeling of said versions of the Vector agrees with that statement.
Initially, after Henry's report was released, I was happy letting things in this discussion cool down, it is something that needed to happen. But then, as I watch essentially the same discussions and close to the same lines being used over and over with little to no progress being made, I guess I am disappointed. HomerBB said:
I agree with this statement 100%, however, I wonder if, when it comes to this antenna, be it past experience or whatever, we no longer seem to be able to push forward and learn or even fully discuss what we think is going on.
The DB
The other thing, when referring to the Vector antennas as being j-pole like. That is fine, I don't necessarily disagree, but that also comes with stipulations that are not being discussed. Its like a general statement is being treated as a fact, but the details that can disagree with said general statement are being ignored. As I recall, there were three different lengths for this antenna, ranging from 3/4 wavelengths to 7/8 wavelengths, as well as a few other recommended lengths thrown out as well. Can anyone honestly say that all of these lengths will act like a stub fed 1/2 wavelength antenna? I'm sorry, but to me at best that seems like a stretch, and my modeling of said versions of the Vector agrees with that statement.
Initially, after Henry's report was released, I was happy letting things in this discussion cool down, it is something that needed to happen. But then, as I watch essentially the same discussions and close to the same lines being used over and over with little to no progress being made, I guess I am disappointed. HomerBB said:
I agree with this statement 100%, however, I wonder if, when it comes to this antenna, be it past experience or whatever, we no longer seem to be able to push forward and learn or even fully discuss what we think is going on.
The DB
Personally, I was ready to let things cool off, too. However, the cooling off came a little late to save some well informed folks from abandoning a very good topic. Friendships and trusts seemed to have gone from warm, to cool, to cold...
I never changed my point of view. I said all along that my experience with the Nv4k gave me better results than other monopole antennas. I said I did not believe it was "just a j pole" meaning it was only a baseline 1/2^ with a really large matching section. To that end perhaps Eddie's sense of the j pole's "sleeper" status needs exploration, however, that the j pole is just an unremarkable okay antenna is how it is generally presented to be as if the S4/V4k are nothing special because they are 'just jpoles".
I really don't care what they are. Invent a new name. Call them pumpkins (I like artichokes)... what I do care about is honest appreciation for the exceptional performance it has been known to deliver.
If Marconi wishes to call it a j pole, then when his own models show it is better than either the j pole or the skeleton sleeved monopole decide to explore whether the j pole is under appreciated, I'm okay with that, too. If it's, back under examination from any angle I enjoy the conversation.
Saying it performs as it does only because it is sticking up higher in the air does not explain what is going on in Marconi's models.
There are potential reasons for why one antenna can do noticeably better for one person than another - topography, soil conductivity, interaction with structures, feed line losses, etc.
BUT, none of those exist in the models of the three antennas compared by Marconi.
To bring them up now whether directly or by inference is only a subterfuge and distraction.
I would be interested in more knowledgeable people than me discussing other aspects of Henry's thesis. Git ur dun.
I never changed my point of view. I said all along that my experience with the Nv4k gave me better results than other monopole antennas. I said I did not believe it was "just a j pole" meaning it was only a baseline 1/2^ with a really large matching section. To that end perhaps Eddie's sense of the j pole's "sleeper" status needs exploration, however, that the j pole is just an unremarkable okay antenna is how it is generally presented to be as if the S4/V4k are nothing special because they are 'just jpoles".
I really don't care what they are. Invent a new name. Call them pumpkins (I like artichokes)... what I do care about is honest appreciation for the exceptional performance it has been known to deliver.
If Marconi wishes to call it a j pole, then when his own models show it is better than either the j pole or the skeleton sleeved monopole decide to explore whether the j pole is under appreciated, I'm okay with that, too. If it's, back under examination from any angle I enjoy the conversation.
Saying it performs as it does only because it is sticking up higher in the air does not explain what is going on in Marconi's models.
There are potential reasons for why one antenna can do noticeably better for one person than another - topography, soil conductivity, interaction with structures, feed line losses, etc.
BUT, none of those exist in the models of the three antennas compared by Marconi.
To bring them up now whether directly or by inference is only a subterfuge and distraction.
I would be interested in more knowledgeable people than me discussing other aspects of Henry's thesis. Git ur dun.