End Fed 1/2 wave antenna

[Marconi]

Perhaps it misses your point.
1. I believe an ounce of prevention is worth a pound of cure.
2. If there is no reason not to have one there is no harm.
3. In my experience using a choke flattens the sharpness of my SWR curve. No, it does not lower the SWR on the center frequency, it causes it to be less sharp having a broadening effect.
4. No, I did not test for TVI/CMC. I simply pulled it from behind the shed in the junk pile and put it in the air so as to see if the flatside would improve my opportunities for DX.

I will go back and look for your models for a dipole at various heights. I will assume it modeled a 27 MHz dipole until I look at it.

Right before I posted the recap of my horizontal 1/2 wave dipole, I did post two models of my idea for your dipole antenna. Maybe you missed it. You can easily see what Eznec shows might happen with the mast/feed line currents noted in red...at 36' feet in height, connected direct to ground, and isolated.

I get it that you weren't looking at CMC issues, and I didn't know you had a choke, I wasn't even sure it was isolated either. I did the recap just to show that isolation might not make that much difference, and to try and show what might happen at different heights. My height issue thing was a consider for me because my Eznec results fly in the face of a common belief... that 1/2 wave and multiples in antenna height is the best height for installing CB antennas.

I understand all of your common sense points, but I tend to explore things a little more in depth looking for information that might support or refute some of my ideas and experiences. Example is my discussing a choke with Bob who brought up the issue for his buddies scenario...which unfortunately may never be resolved.

Contrary to popular belief, I don't make this stuff up. I just try and figure out what it all means, and I don't depend on tried and true CB ideas...especially when I see conflicts in my own results.

Bob and I have discussed my idea that CMC may be somewhat affected by the length of the mast/feed line. I sited W8JI's idea of "...worst case scenario." I think he disagreed with me on that idea back then, but I'm not sure of his views on that subject now.

With some exceptions all of my models are done at 27.205.

Homer, I didn't wish you to go to any trouble in testing, and that is why I asked you what you saw when you removed your coax choke from your A/P, but you tell me now that didn't happen, so I was wrong in my recollections.

I often see this resistance to answer questions as soon as I start to ask.

 

[nav2010]

I've just done an important test Between an Antron99, an Imax and the new Gainmaster. Having watched Marconi's tests on you tube and being impressed by the way he conducted the tests, I decided to do my test the exact way that Marconi did his. This is a breakthrough I believe and important data.
Antron99 v Imax2000 v gainmaster - YouTube

 

[Marconi]

Nav2012, that is funny. Reminds me of a Benny Hill skit.

One problem though you didn't show the meter responses. So, what does you test show us, that you have sense of humor?

Nav has <gotproof>

 

[Henry HPSD]

Lol...nice vid!

so much text...it is difficult to read the questions.
(dont worry it is because of me..)
If i may ask..what is the question (s) needed to be answered ?

Kind regards,

Henry

 

[HomerBB]

Marconi, of all people I try to answer as many of your questions as I can. Sometimes I don't know the answers. Sometimes I do.

Right now I do not have an AP. Someone needed an antenna to get on the air and was willing to part with an exorbitant amount of cash - $35 - to own the homebrew AP. I couldn't refuse so much money so I let it go. I still have a dipole and an EFHW to play with, and parts of others lying around.
I will build me another AP.
And I will fit some silly GPs from a previous experiment on the EFHW, and I will rebuild my V4k, and I will remount my 4el Yagi, and I will . . . answer as many questions as I know the answers to along the way. When I can't do that I will help you scratch your head by scratching mine. Just tell me when it is time to scratch my head.

 

[Marconi]

Lol...nice vid!

so much text...it is difficult to read the questions.
(dont worry it is because of me..)
If i may ask..what is the question (s) needed to be answered ?

Kind regards,

Henry

Henry, I just discussed in a post to NB, what I thought about this thread and it has become complicated by our trying to discuss several topics.

Homer posted the thread talking about his end fed 1/2 wave antenna. Then it got off into an elevated horizontal 1/2 wave dipole.

Bob raised an issue about a buddy with TVI problems on an end fed 1/2 wave I think.

And I was trying to reply to all points and then I brought up the subject of the gain for a 1/2 wave dipole per Homer's response that his horizontal dipole had no gain.

Like I said it is confusing for me too, and I played a part in such confusion.

Did you ever get the Eznec model of my I-10K with the trombone matcher I sent you?

 

[Marconi]

Marconi, of all people I try to answer as many of your questions as I can. Sometimes I don't know the answers. Sometimes I do.

Right now I do not have an AP. Someone needed an antenna to get on the air and was willing to part with an exorbitant amount of cash - $35 - to own the homebrew AP. I couldn't refuse so much money so I let it go. I still have a dipole and an EFHW to play with, and parts of others lying around.
I will build me another AP.
And I will fit some silly GPs from a previous experiment on the EFHW, and I will rebuild my V4k, and I will remount my 4el Yagi, and I will . . . answer as many questions as I know the answers to along the way. When I can't do that I will help you scratch your head by scratching mine. Just tell me when it is time to scratch my head.

I'll try to remember to remind you. I know it's hard to say, we don't have an answer, when we don't have an answer.

That's sounds to me like putting a choke on an antenna, when we don't even know we really need a choke. :headbang Did you read what Cebik said in the highlighted part of the link I posted?

Homer, my point is that this all has to do with a distinction for when CMC are bad vs. when good, or when they're low in magnitude and just don't matter. The bases of my idea is based on some experience, but primarily is supported with the two models I posted.

I'm not giving you just words Homer. I attempt to answer the question I always have, when guys tell me that adding a choke to their antenna made a difference.

If you look at how much difference these two models indicate, do you really think you could ever detect such a difference just using your radio? It could be in your location that the choke is helpful to stop TVI and that is good, but as a distinction take for example a station in the country side where these currents might not hurt at all, and that is what these models might be suggesting.

So, I ask, "...how much difference does adding your choke make?" You could try it and find out it made a big difference in TVI or maybe not, because I picked the worst case scenario according to my models, then you could tell me, "I told you so." This is the same situation that I posed to Bob earlier, hoping he could convince his friend to try an elimination process trying to figure out what is affecting what.

 

[Henry HPSD]

Hi Guys,

It is understood (at least for me) it became difficult to read.

No, it doesnt ring a bell Marconi
(your question.. if i got the model, i dont think i have..i migth have though.
If there is something you need to know just drop an email)

Well if there are quetions i am more than willing to think along...

Kind regards,

Henry

 

[Needle Bender]

Right now I do not have an AP. Someone needed an antenna to get on the air and was willing to part with an exorbitant amount of cash - $35 - to own the homebrew AP. I couldn't refuse so much money so I let it go.

Wait a minute, you sold a pvc astroplane covered with aluminum foil for $35?

If so that's gotta be the funniest thing I've heard in my 40 years of playing radio!! :w00t:

And Marconi, I am under the possibly mistaken impression that two stations 10 miles apart hitting each other with s9+10 while each is using a vertical dipole will see an s9+22.5 if both were to switch to a broadside horizontal dipole at the same relative height, each getting about 6.25dB ground gain over the vertical dipole.

Bob85, I've never had a CB type radio with FM, only amateur rigs, Yaesu, Kenwood and Icom, and their meter/AGC has always confounded me with it's propensity to want to jump to full-scale with only slight gain or the smallest improvements made over an s9 on FM. :glare:

 

[Marconi]

Hi Guys,

It is understood (at least for me) it became difficult to read.

No, it doesnt ring a bell Marconi
(your question.. if i got the model, i migth have though.
If there is something you need to know just drop an email)

Well if there are quetions i am more than willing to think along...

Kind regards,

Henry

I'm not surprised it is hard for me too, that is why I told NB, I didn't want to go back and try and decipher, and read his mind, trying to figure out what he didn't understand.

Here is my thread, where I try to explain the thread as I understand it.

NB, I can't be for sure what I said now, and I don't want to go back and try and decipher what might have corn'fused you, but I think my main point was regarding the W8JI idea about the gain of a dipole.
Homer told us his horizontal probably had no gain, and you questioned that.
So, I looked up the source of the claim that a dipole had 8.5 db gain. I think it was Bob that first mentioned this idea to me, and it was published by W8JI.

I then modeled a horizontal 1/2 wave dipole and did a recap of the details as I raised it up 4.5' each time from 9' to 54'. I did the model with a mast that was not isolated, and a model that had no mast at all. I was thinking to compare a 1/2 strung between two trees vs. one supported on a mast with a direct connection.

View attachment 7451

At that point in time Homer hadn't said how his horizontal dipole was supported, so I assumed it was probably isolated with PVC, but I ended up making his model grounded instead, and I discovered later that was an error.

So I messed up there.

If I could, I would do it over and delete the previous report or add a model with an isolated mast, but sometime when I make a mistake...the whole point gets lost in the added confusion trying to fix it. My whole point in doing these models was to try and prove what W8JI suggested about the 8.5 db gain using 75/80 meters. I didn't prove the 8.5 gain, but it surprised me a little that the horizontal dipole showed 7 db+ vs. about 3 db+ for a vertical dipole.

BTW, I wasn't even thinking about an isotropic comparsion like W8JI was discussing, a distinction that must be considered for his claim.

This is why sometimes trying to show evidence in support of my words can get out of hand, and then with the confusion nobody cares what the point is.

I don't know if Homer's dipole has any detectable gain or not, but he did later state his reason for saying that it had no gain. He said it was because the dipole is the standard of comparison for all antennas.

That stimulated me to wonder which dipole do we use then...as the standard, the horizontal or the vertical dipole.

We were talking about end fed 1/2 wave antennas for 11 meters, and W8JI just used the word "dipole" in his remarks, and then he showed us a model of a 75/80 meter horizontal dipole, so I was just trying to connect the dots.

I considered this recent report from W8JI needed to be fleshed out a bit, and I apparently ended up sounding like I was talking Greek.

I was also trying to discuss Bob's topic on his buddies antenna fix on a TVI problem.

Homer was talking about his end fed half wave (EFHW) which is the subject of his thread.

I was trying to talk about both subjects and then I interjected the W8JI idea.

So, is there any wonder you are confused?

I'm as guilty as anybody of getting off point in these conversations at times, but that's about the state of this conversation...me thinks.

Sorry NB, but you'll just have to take your pick, and if I mis-stated anybodies postion or idea here, then I'm sorry for that too.

Henry, like I suggested to NB, take your pick.

 

[Needle Bender]

Homer, I've made the claim that 36' feet of mast or coax to the ground is likely a worst case scenario for CMC on several antennas I've tested with Eznec. So, you're probably right to add a suitable working choke, but how do you really know the choke is working as intended?

I believe any odd multiple of a 1/4 wave (multiplied by about a 95%-98% vf for casing impedance) would tend to do more errant radiating since a straight run full wave of about 36' offers self-cancellation, due to radiating both the full positive and full negative current nodes. That's why a full wave vertical is such a poor antenna, it offers too much self-cancellation.

 

[bob85]

nb,
odd multiple 1/4waves to rf ground create a high impedance and little cm current, 1/2wave multiples create a low impedance to ground or w8ji's worst case scenario for cm currents,

from w2du's excellent reflections series

Chapter 21, Some Aspects of the Balun Problem

 

[HomerBB]

I'll try to remember to remind you. I know it's hard to say, we don't have an answer, when we don't have an answer.

That's sounds to me like putting a choke on an antenna, when we don't even know we really need a choke. :headbang Did you read what Cebik said in the highlighted part of the link I posted?

I received the notice with the link for the Cebik article on my phone while on the job. I didn't have time there to read it in depth, and by the time I got home the thread had gone on passed it. I will go read it all.

Homer, my point is that this all has to do with a distinction for when CMC are bad vs. when good, or when they're low in magnitude and just don't matter. The bases of my idea is based on some experience, but primarily is supported with the two models I posted.

I'm not giving you just words Homer. I attempt to answer the question I always have, when guys tell me that adding a choke to their antenna made a difference.

I see your point, most definitely. I have no issue with it, I just always put one in line . Besides, when I make them nice and neat they look kinda cool.

If you look at how much difference these two models indicate, do you really think you could ever detect such a difference just using your radio? It could be in your location that the choke is helpful to stop TVI and that is good, but as a distinction take for example a station in the country side where these currents might not hurt at all, and that is what these models might be suggesting.

I have heard my radio speak several different languages, most of which I barely understand, and mostly all at one time, so I doubt I can tell the difference with just my radio, however, when I put a choke in line and the bandwidth softens at the edges and is broader, I do like the way it looks. It's like the difference a gal looks in an evening gown and a croaker sack.

So, I ask, "...how much difference does adding your choke make?" You could try it and find out it made a big difference in TVI or maybe not, because I picked the worst case scenario according to my models, then you could tell me, "I told you so." This is the same situation that I posed to Bob earlier, hoping he could convince his friend to try an elimination process trying to figure out what is affecting what.

I might could take it off and see, but at this point I just can't answer that.
To the point of using it if I don't need it, I may have to reconsider filling my gas tank up on Tuesday when all the driving I'll do that day is a mere 10 miles. I just hate to pump gas, and filling it up prevents me even having to for the week. Maybe I don't need a choke, but what if I do. I do have a few of neighbors, and Cox cable was around the neighborhood a month ago hunting for a 27 MHz spike that was getting into their stuff, so I have cause for caution.

My place is under the red pin:

 

[HomerBB]

Wait a minute, you sold a pvc astroplane covered with aluminum foil for $35?

If so that's gotta be the funniest thing I've heard in my 40 years of playing radio!! :w00t:

I once added up how much I spent at the store for what I needed to build it including the bracket metal, spreader material, roll of foil tape, CPVC and PEX tubing. U-bolts, SS screws, top hat rods, etc and it came to $27.50. That's not to mention the two (2) $17 each aluminum mast poles I let him have , one $10 steel mast pole, and 52' of coax cable for a paltry sum of $35. I lost money, but gained satisfaction.
He's on SSI due to paralysis from stroke. He insisted that I take something for it and thought he could do the $35.

If he doesn't have the cash after the 1st of the month I'll just give it to him if he'll let me.

 

[Marconi]

I believe any odd multiple of a 1/4 wave (multiplied by about a 95%-98% vf for casing impedance) would tend to do more errant radiating since a straight run full wave of about 36' offers self-cancellation, due to radiating both the full positive and full negative current nodes. That's why a full wave vertical is such a poor antenna, it offers too much self-cancellation.

NB, I didn't post these models trying to cut down on the work, but here are two of the models to demonstrate what Eznec indicates regarding your idea that a 1/4 wave or odd multiples will show the most errant currents. The top model is a 36' feet 1 full wavelength or an even number of 1/4 waves. The other is 27' feet 3/4 wave or an odd number of 1/4 waves. This is as simple of an antenna as we can get, and you can easily see what is going on with the currents.

I added the current data report that shows only 1 segment per wire. This shows all the current in a single value for each wire. The value is in amps or fractions.

The red lines on the antenna views were taken correctly, with a modest number of segments per wire, which resulted in each segments being equal at 1' foot each on each wire.

If you have any questions then let me know, and I'll try and answer.

View attachment NB's idea on height.pdf