End Fed 1/2 wave antenna

[Needle Bender]

Well Homer I've been reading around a lot, as well as a bunch of old threads here, and it just makes sense to me, but I'm not the know-all & end-all in the knowledge basket, just a learner walking through life watching & listening, trying to learn.

That's why I've devised a definitive test which will show beyond all possible questionable doubt just what that big aluminum ice cream cone really does.

I kinda hope I'm mistaken about it and that the whole bloody thing radiates, making it the biggest & bestest out there, but I have my doubts.

Also, I know it takes a full additional 1/2 wave mounted at least a half wave above the first in order to achieve 2.15dB gain from a 2 element colinear array and there's only a possible additional 1/4 wave below the top 1/2 wave on the vector, so there's nowhere near enough antenna nor element spacing to provide colinear gain of more than a small fraction of a dB, if that was how it operated.

Makes sense that it's simply a full 1/2 wave with the same 1/4 wave null below it that the end-fed 5/8 also has, helping it to achieve a lower TOA like the 5/8, except with 33% - 1dB more radiator.

Again, it's only my best guess and I'll know for certain once I get the test completed. :mellow:

Bob, like you, I just gotta try it for meself

 

[HomerBB]

I see. Someone else will have to take up.
I keep my debates simple:
@ 11 meters
9' =1/4
18 = 1/2
22.5 = 5/8
27 = 3/4

More or less . . .
Coils/traps/inductors can affect that,
And how much is trial and error for me.

 

[HomerBB]

I just put this one in the air at 36' this afternoon. So far it is doing a good job with DX. It is a 1/4 hooked to a 1/4 and fed normally. That should make it a common dye-poe with no gain to speak of, but my receive is full of DX this afternoon. I am hearing from Austrlia to New York and Toronto, CAN. I expect any moment now to bust out into Asia . . . Okay, just being silly, but the dipole is working it out surprisingly well. That's why you have to like them.

When I'm not so tired I may get to fiddling with that 1/2 wave, Marconi . . . maybe.

Another interesting graphic I ran across here: The Dipole at varying heights. I wish it would go a little slower.

 

[Needle Bender]

But wait, - it DOES have gain, ground gain!

Any horizontal has about 6 1/4 dB ground gain over a vertical of equivalent design, so you're reaping the benefits of horizontal polarization!

- But, you knew that!! :tongue::laugh:

 

[HomerBB]

I was teasing you on account of the run down of gain on several antennas you provided with your previous post.
I agree, there is something to gained with the horizontal over vertical at similar heights, at least in my experience.

 

[Needle Bender]

I was teasing you on account of the run down of gain on several antennas you provided with your previous post.
I agree, there is something to gained with the horizontal over vertical at similar heights, at least in my experience.

I HEAR that!

 

[bob85]

tv issue solved again, he had moved the tv, ferrite on the mains lead cured it,
for now

 

[Marconi]

But wait, - it DOES have gain, ground gain!

Any horizontal has about 6 1/4 dB ground gain over a vertical of equivalent design, so you're reaping the benefits of horizontal polarization!

- But, you knew that!! :tongue::laugh:

I think there is some misunderstanding created by the words where W8JI describes a 1/2 wave dipole as having 8.5 db ground gain over a isotropic, whatever the gain difference is Needle Bender. See here: End-fed Vertical and J-pole

Not only is W8JI talking about a 75/80 meter wire dipole that is very high due to the 1/2 wavelength at that frequency, he is referring to a horizontal dipole.

This may be technically what is happening, but IMO and to be clear, I see this difference is due to the directional qualities with a horizontal dipole vs. a vertical 1/2 wave dipole, so there is a distinction that has to do with the difference between a vertical and a horizontal...and that has to be considered in your thinking.

For me, this is exactly how CB BS gets started, taking things completely out of context.

Homer, you horizontal dipole probably does have some gain as NB notes. Here is a model as <gotproof> of the considerations I note above. I don't see 8.5 db
gain, but that could possibly be due to the difference in the frequencies and heights noted by W8JI. I have not modeled the 75/80 meter idea that W8JI presented, but I would suspect there might be differences in results vs. 11 meters.

NB, when you read those words stating that a dipole really has a 8.5 db gain...did you consider that W8JI was likely referring to a horizontal dipole?

Did he suggest in his words that he was referring to a horizontal dipole?

Can you tell in his 80 meter pattern example that he was referring to a horizontal dipole?


Do you think such a distinction should maybe be noted in his words?

I'm not always right, but IMO if you don't read the words, you aren't likely to get the full story...by just looking at the pictures. And, sometimes if the words don't tell the full story, you aren't likely to get the full story either.

View attachment Homer's CB .50 wave dipole.pdf

 

[Marconi]

tv issue solved again, he had moved the tv, ferrite on the mains lead cured it,
for now

So Bob, are you telling us your fix idea didn't work after all?

Did you ask him why he moved the TV, since the problem had been fixed?

 

[HomerBB]

I think Bob's fix worked. The efficacy of any particular solution is tied to the variables inherent to the location where the problem exists. Moving the TV changed the variables. New measures were called for.

Now, how that relates to this TVI/CMC fix in relation to the ground plane radials and antenna isolation on an EFHW is altogether another matter. It would seem the radial debate is not to be conclusively resolved using Bob's anecdotal example.

BTW, no animals were harmed in the typing of this post.

 

[Marconi]

I think Bob's fix worked. The efficacy of any particular solution is tied to the variables inherent to the location where the problem exists. Moving the TV changed the variables. New measures were called for.

Now, how that relates to this TVI/CMC fix in relation to the ground plane radials and antenna isolation on an EFHW is altogether another matter. It would seem the radial debate is not to be conclusively resolved using Bob's anecdotal example.

BTW, no animals were harmed in the typing of this post.

Well Homer, I posted an exception that W8JI highlighted in his piece on "RF in the Shack," so I guess now that shouldn't be ignored.

For me the logical thing for Bob to consider would be to place the coax choke as close to the problem as possible, at the feed point...assuming the problem was CMC, and not RF directly from the antenna.

I don't recall your answering me before regarding a some what similar idea, but I asked you what happened with your A/P when you removed the choke...that was well below the hoop by 8'-9' feet?

Do you think Bob's idea for just adding the choke 18' feet below the bottom of the A99 was similar to your thinking in that case?

IMO our buddies over there in England likely have heavy third party influence on whatever they do or don't do with their own physical property, so they tend to mount their antennas down real low, and that is probably what the exception idea that W8JI's warning was referring to.

So what do we do in light of this exception, just ignore it?

I know that chokes can work effectively where ever the antenna is placed, because I have a Gain Master and that one as <gotproof> if for me.

But, IMO very few even consider that a real feature with the GM, and most probably give no thought to an idea that the antenna itself can cause TVI, it's always something else. In my experience the fix on the GM has worked to produce no CMC...no matter where I placed it so far. I think that is the way a fix should work if CMC is the issue, and not the antenna.

 

[Needle Bender]

I think there is some misunderstanding created by the words where W8JI describes a 1/2 wave dipole as having 8.5 db ground gain over a isotropic, whatever the gain difference is Needle Bender. See here: End-fed Vertical and J-pole

Not only is W8JI talking about a 75/80 meter wire dipole that is very high due to the 1/2 wavelength at that frequency, he is referring to a horizontal dipole.

This may be technically what is happening, but IMO and to be clear, I see this difference is due to the directional qualities with a horizontal dipole vs. a vertical 1/2 wave dipole, so there is a distinction that has to do with the difference between a vertical and a horizontal...and that has to be considered in your thinking.

For me, this is exactly how CB BS gets started, taking things completely out of context.

Homer, you horizontal dipole probably does have some gain as NB notes. Here is a model as <gotproof> of the considerations I note above. I don't see 8.5 db
gain, but that could possibly be due to the difference in the frequencies and heights noted by W8JI. I have not modeled the 75/80 meter idea that W8JI presented, but I would suspect there might be differences in results vs. 11 meters.

NB, when you read those words stating that a dipole really has a 8.5 db gain...did you consider that W8JI was likely referring to a horizontal dipole?

Did he suggest in his words that he was referring to a horizontal dipole?

Can you tell in his 80 meter pattern example that he was referring to a horizontal dipole?


Do you think such a distinction should maybe be noted in his words?

I'm not always right, but IMO if you don't read the words, you aren't likely to get the full story...by just looking at the pictures. And, sometimes if the words don't tell the full story, you aren't likely to get the full story either.

View attachment 7443

I was referring to his horizontal 1/2 wave dipole pictured in his post.

 

[Marconi]

I was referring to his horizontal 1/2 wave dipole pictured in his post.

NB, I wasn't referring to anybodies antenna.

I was trying to suggest there is a distinction to be made when guys talk about the 1/2 wave dipole having 8.5 db gain over an isotropic. I remember saying those words in my post.

You noted the distinction in your post below, but W8JI never mentioned a word about the subject antenna being a horizontal dipole, he just said dipole.

But wait, - it DOES have gain, ground gain!

Any horizontal has about 6 1/4 dB ground gain over a vertical of equivalent design, so you're reaping the benefits of horizontal polarization!

- But, you knew that!! :tongue::laugh:

A vertical 1/2 wave dipole will not have anywhere near a 8.5 db gain, and I would be willing to bet that plenty of guys reading his article came away thinking all dipoles had 8.5 db gain over an isotropic just because W8JI said it...like it was something new in antenna theory that he just discovered.

I was reminded of this because Homer said his horizontal dipole probably had no gain. Some folks have recently suggested that a dipole had 8.5 db gain and didn't bother to explain this distinction. This is probably where Solarcon got their idea that the A99 have something like 9+ db gain by twisting the truth...

W8JI goes on to better explain what he meant toward the end of his article, but most guys probably don't even bother to read past the point that cements their own idea on a topic if they read the article at all.

Again I'm talking about more CB BS, and you'll find it is confusing and hard to understand just like the truth is at times.

Here are some results of a horizontal dipole with and without a mast at various heights. I think Home's dipole is probably isolated from the mast. I didn't isolate the models with the mast, but you will notice how similar the results are between the models with a mast vs. those without a mast. In this case there is no better isolation to be made in modeling. Of course in real life we would have to bother with the feed line.

View attachment Eznec's idea of Homer's Horizontal Dipole..pdf

 

[bob85]

eddie,
i can't see the sense in choking the feed-point then running coax down the mast that's not isolated for rf to couple back into the coax, that's why it was placed just below the mast, no point in isolating the mast if you have no radials as the choke won't work if there is nowhere but the coax braid for common mode currents,

did it work? yes at least to some extent as his rfi went away with 100w after weeks of trouble,
then he moved the tv closer to where the coax enters the house and closer to the mast on the side of the house, his trouble came back worse than ever.

try modeling homers dipole 1/2wave @27mhz above ground, you won't see 8db gain if its much higher.

 

[Marconi]

eddie,
i can't see the sense in choking the feed-point then running coax down the mast that's not isolated for rf to couple back into the coax, that's why it was placed just below the mast, no point in isolating the mast if you have no radials as the choke won't work if there is nowhere but the coax braid for common mode currents,

did it work? yes at least to some extent as his rfi went away with 100w after weeks of trouble,
then he moved the tv closer to where the coax enters the house and closer to the mast on the side of the house, his trouble came back worse than ever.

try modeling homers dipole 1/2wave @27mhz above ground, you won't see 8db gain if its much higher.

I was probably posting my results of what I see using Eznec as you were typing your post. Check the link out at the bottom of my previous post. I don't see 8+ gain, but I do see close at 7+ at 18' feet and this was in response to Homer's claim that his elevated horizontal dipole probably had no gain. The difference in 8+ and 7+ could be due to the difference in frequencies used to test.

I don't understand why you chose not to isolate either. I have considered that maybe when we effectively choke the feed line that the affect will also apply to the mast. I guess for that to happen, the antenna would have to have the need for a counterpoise resolved before hand, and that leads to my original conclusion that maybe the A99/Imax tuner provided all the return current needs in the matching device, and that need for the counterpoise was very small compared to the wavelength. That is what all that testing that Homer did at my request, to see if adding a radial made a difference on his setup.

For me, an easy way for your buddy to test this paradox would be to move the TV right back to where is was and see if the fix would repeat. Then remove the choke and move the TV to the new spot and then see what happens. A little imagination and "what if considerations" might help answer these questions. I know you and I both were surprised at such good results turning bad so suddenly.

Personally, I believe the antenna could be producing the TVI noted on the TV, but I doubt that will ever be proved no matter what changes are made.

Personally I have chased my tail trying to figure out similar anomalies here at my location, because I didn't understand what was going on, but I figure I'm wrong a lot more than you guys will ever be.

Again Bob, you didn't bother to answer my question regarding why your buddy decided to move the TV.