End Fed 1/2 wave antenna

[Marconi]

Homer according to Yates, the matching section he and Mozon's idea uses has .05 wavelength of added counterpoise on each side of the secondary capacitor at 14 mhz...if I understand what is written.

Do you find that your 1/2 wave is a little longer than you expected?

Did you have to make your radiator longer in the process of tuning?

I realize you're using tubing and Yates used wire, so there would be a physical difference, so maybe their idea for a counterpoise being necessary in this area around the capacitor, and they're adding some inductance by making parts of the matcher longer is what is at work to provide that counterpoise.

This high impedance and low current idea they present is my reason to claim that an end fed 1/2 wave A99 does not need radials, just said a different way. I've been suggesting this for a long time, even before I read this article. No body has ever questioned this link that I recall, but this part is exactly why I support this Yates idea.

Again, for a long time I have said, how can radials work effectively at the voltage end of a 1/2 wave radiating element where there is virtually no current flowing. I've tried to measure current in the radials with a clamp on amp meter, but I never saw the dial move one bit.

I have to say I never did this test with the antenna isolated though, else I will be put on the rack for sure. I just reasoned, thought about it, and then tested.

How say you?

View attachment AA5TB on EFHW antennas..pdf

 

[HomerBB]

Homer according to Yates, the matching section he and Mozon's idea uses has .05 wavelength of added counterpoise on each side of the secondary capacitor at 14 mhz...if I understand what is written.

From the look of the diagram in the .pdf, it appears the counterpoise id 0.05 wavelength long, and an extra 0.05 wavelength is added to the half wave radiator.

Do you find that your 1/2 wave is a little longer than you expected?

no. it is about 18' long, i=I think 18' 2".

Did you have to make your radiator longer in the process of tuning?

no, that is, not longer than a 1/2 wave. The dipole had tuned shorter than a full half wavelength long, so when I re-purposed it for this end fed project, I lengthened it.

I realize you're using tubing and Yates used wire, so there would be a physical difference, so maybe their idea for a counterpoise being necessary in this area around the capacitor, and they're adding some inductance by making parts of the matcher longer is what is at work to provide that counterpoise.

Yes my antenna is tubing, not wire. Whether that is a reason for my results with or without the radial I don't know. I know only the analyzer showed the best numbers, and almost negligibly so, without a radial.

This high impedance and low current idea they present is my reason to claim that an end fed 1/2 wave A99 does not need radials, just said a different way. I've been suggesting this for a long time, even before I read this article. No body has ever questioned this link that I recall, but this part is exactly why I support this Yates idea.

Again, for a long time I have said, how can radials work effectively at the voltage end of a 1/2 wave radiating element where there is virtually no current flowing. I've tried to measure current in the radials with a clamp on amp meter, but I never saw the dial move one bit.

I have to say I never did this test with the antenna isolated though, else I will be put on the rack for sure. I just reasoned, thought about it, and then tested.

How say you?

View attachment 7401

I don't know about all this, but you are right, an argument that departs from conventional wisdom will be a difficult one to sell, after all, observe the Sigma 4/Vector 4k threads miles long, and only one or two people have emerged from that discussion willing to say they had come to a personal conclusion regarding what the antenna is, and how it works. Others just hang on to the arguments they've enjoyed hearing for a long time.

About this idea you are working, there is so much history of seeing things a particular way that not many want to rearrange their thinking to even discuss it. What many forget is the ideas they take for granted nowadays was an impossible, unbelievable batch of snake oil at another time. Ultimately, things like this when discussed may not result in a different conclusion, but a willingness to pursue a different train of thought at least for a little while is always profitable for the sake of clarifying some things for some who otherwise may never know.

 

[Marconi]

Yes Homer you're probably right.

I guess this sorta' proves the old saying, maybe we should just keep our ideas to ourselves, and forget about trying to prove anything. It sure would be a lot easier.

I like your last conclusion and it would be nice, but I really doubt that works out like you said.

Again, thanks for your help.

 

[M0GVZ]

This high impedance and low current idea they present is my reason to claim that an end fed 1/2 wave A99 does not need radials, just said a different way. I've been suggesting this for a long time, even before I read this article. No body has ever questioned this link that I recall, but this part is exactly why I support this Yates idea.

Again, for a long time I have said, how can radials work effectively at the voltage end of a 1/2 wave radiating element where there is virtually no current flowing. I've tried to measure current in the radials with a clamp on amp meter, but I never saw the dial move one bit.

Kirchoffs 1st and 2nd law??? All I know is an Antron 99 on a short alloy pole without a choke on the co-ax results in a RF hot mike at 50W.

 

[Marconi]

Kirchoffs 1st and 2nd law??? All I know is an Antron 99 on a short alloy pole without a choke on the co-ax results in a RF hot mike at 50W.

Let me ask you M0GVZ, what exactly happens when you experience the A99 condition you note above?

 

[Marconi]

M0GVZ here is a page from a report "Verticals and Baluns", by W8JI, a guy I'm sure you and Bob respect. He states an exception to the general rule as it applies to the issue..."RF in the Shack."

The exception is highlighted in blue about mid-page. I ask, since you had your A99 on a 10' foot pole during your bad experience with mic shock, is there any doubt that maybe your scenario falls within the exception as noted by W8JI below, rather that RFI and mic shock is just a categroical result with all A99s...when mounted very low to the Earth?

View attachment Verticals and Baluns by W8JI.pdf

With all the 1000's of A99's that must be in use around the world, do you really think they all suffer from RFI so bad as to cause a hot mic when testing at about 10' feet above the Earth? That is not a regular height for a CB install, but it might be about right for guys checking the match or making ring adjustments. We hear many complaints for the A99, but how often do we hear such complaints as you've noted?

I mess with my antennas a lot, and I've never had a hot mic on any antenna I've ever had up at any height. I have heard of cases for such things of course, but it has never happened to me, and I find it hard to believe that all A99s mounted on a 10' foot pole are likely to respond with mic shock...as you have suggested. Could this maybe be an exception like W8JI talks about. How about you Bob, same questions.

The only issue I note with my A99 and most other CB vertical antennas I have when mounted low is; they don't perform well in the direction of my roof peak...when the bottom of the antenna is below the peak level and my roof is not made of conductive type materials. I see that a lot in pictures from your area, so I guess the limits in height are at issue.

I'm also going to post another thread of an Eznec5 report I did for both an Imax/A99 at various heights above Earth, to show what Eznec suggest at 9' to 76.5' feet. I used the same model for each 4.5' iterations on raising so that I could show CB multiples for a 1/4 and 1/2 wave while going up.

I think this is probably more revealing of what could happen with bad currents on the mast and feed line, if we were to be lucky and be able to get the height right on the money...just using a standard idea for a 1/4 wave at 9' feet. You may also note that the random heights in between the multiples of a 1/2 wave, show to perform better with the currents on the mast, and the high angle lobes in the patterns when we get above about 27' feet.

If nothing else, you may at least note how sensitive that Eznec suggest height is to antennas.

 

[bob85]

i have no doubt the a99 uses the mast/coax and can have hot coax in some situations, you would likely never notice even a worst case setup unless running significantly more than 4w,

we fixed another imax with radiating coax a few days ago, no isolation or radials,
a choke wound just below the 18ft mast mounted on the side of the house cured weeks of 100w tv remote control

 

[Marconi]

i have no doubt the a99 uses the mast/coax and can have hot coax in some situations, you would likely never notice even a worst case setup unless running significantly more than 4w,

we fixed another imax with radiating coax a few days ago, no isolation or radials,
a choke wound just below the 18ft mast mounted on the side of the house cured weeks of 100w tv remote control

I'm not going to touch this one, because I'm pretty sure the situation with your fix doesn't quite fit with the idea I got in reading your fix...with just a choke wound just below the 18' foot mast mounted on the side of the house...that's just not your way Bob.

Robb seems to understand your comment, maybe he can explain to me exactly what you did to fix your buddies automatic TV remote.

BTW, all my models were set with 30 watts of power and the antennas had radials for this project. If I could model the matching situation for the A99/Imax I would, and then I would add the feed line and see what Eznec shows for both antenna without radials.

As stated by the experts any antenna feed line can have bad common mode currents, and maybe a lot has to do with just how lucky we are installing the antenna correctly and avoiding the "worst case scenario".

Bob, you can be tricky with words sometimes, and on occasion I think you have repeated the old claim; that just using a coax choke is often not effective enough to mitigate such problems. So, what you describe here, just doesn't sound to me like your way of fixing a CMC problem.

 

[bob85]

i don't know why you have any trouble grasping what we did,

im not tricky with words, your doubting thomas mind made an incorrect assumption again,

NEWS FLASH "bob's way is whatever works in a given situation"

if you study you will see what i had my local amateur buddy try and why it worked for him.

 

[bob85]

i don't know why you have any trouble grasping what we did,

im not tricky with words, your doubting thomas mind made an incorrect assumption again,

NEWS FLASH "bob's way is whatever works in a given situation"

if you study you will see what i had my local amateur buddy try and why it worked for him.

 

[Marconi]

i don't know why you have any trouble grasping what we did,

im not tricky with words, your doubting thomas mind made an incorrect assumption again,

NEWS FLASH "bob's way is whatever works in a given situation"

if you study you will see what i had my local amateur buddy try and why it worked for him.

I'm having trouble because you didn't tell us exactly what you did. You said the following.

i have no doubt the a99 uses the mast/coax and can have hot coax in some situations, you would likely never notice even a worst case setup unless running significantly more than 4w,

we fixed another imax with radiating coax a few days ago, no isolation or radials,
a choke wound just below the 18ft mast mounted on the side of the house cured weeks of 100w tv remote control

Your description leaves me to assume everything that you did. What does this business mean, a choke wound just below the 18' foot mast? Does that mean the mast was mounted up high above the ground on the side of the house? Are you telling us that the antenna you fixed a few days ago had no radials and was not isolated? Did you add radials and isolate as you're also prone to recommend?

This is why I asked Robb what he thought was going on in your project. I doubt he will respond, are you going to do likewise, and not answer my questions above? I can't hardly have a discussion with you if I have a question and you won't answer.

I answered your question in the first sentence of you post, how about helping me understand better what you did to stop your buddies problems.

We have discussed this idea before and you disagreed then as well. I don't really expect for you to consider my thoughts of this matter, but maybe you can help me understand what W8JI says on the following quote from his article entitled Ham Station Desk Radio Equipment Ground under the topic "Dipoles" quoted below.

There is no universal magic feedline length that minimizes common mode currents in every installation. The length required to minimize common mode varies with feedline routing, grounding, and surroundings. If we have a very specific situation, like a vertical feedline hanging vertically in open air from a dipole center, and that feedline runs straight down to earth and is grounded at earth's surface, we can predict the feedline length to minimize common mode without a balun. The magical length in this specific case is 1/4λ or any odd quarter wavelength of cable length between the antenna feedpoint and ground. Since the primary dielectric between the cable shield and earth or the antenna is air, feedline velocity factor is meaningless! If we inserted a common mode choke right before the ground on the antenna side of the ground, it would maximize common mode problems! We have to be careful throwing parts at a system hoping something will stick.

What my report shows above is that a 1/2 wavelength feed line is probably not the best line length to use for a working feed line, and I've highlighted what W8JI says above on the subject.

I think I've heard you claim, on-the-other-hand that a 1/2 wave or multiples of feed line length is best used to help mitigate CMC from flowing on your feed line, right?

If you read my words in my first post in this thread you will see that I left some wiggle room for my remarks, because I think it would be difficult to find the best scenario for the correct feed line length. Buy I still think it shows how feed line length can affect our installation, both for good and for bad, and that might give us a clue for which way to go to help mitigate such problems with CMC.

Plus maybe you'll remember the story my old radio mentor always told me, keep your working feed lines to random lengths, and stay away from resonant 1/2 wave working feed lines. His description for what that meant was to suggest that a resonant 1/2 wave line will tend to show a low impedance at both ends if the load is properly tuned and every thing else is just right. So, if there are radiating currents on the feed line, they will surely radiate and they can go all the way back to the station...possibly creating erroneous SWR readings and other problems. I've found this to generally be true in my real world experience...and here it shows the same with these models in my report on the Imax/A99.

This idea is not a cure all, fix all for sure, but maybe it might indicate a bit of what can go on that affects our antenna systems.

You're right about one thing for sure, "...whatever works in a given situation is the best way to proceed." So I guess we'll just have to agree to disagree with the rest.

 

[gamegetter]

 

[HomerBB]

Bob, I was going to ask you the same question Marconi asked, "is the setup you helped fix what your post seems to read?"
I read over it more than once and it seems to say that his antenna is mounted with a mast that is 18' long attached at an elevated position on the side of his house. You placed the coax choke at the 18' distance below the antenna feed point to stop CMC on the coax and it did. If I've read it correctly, it would seem your strategy was to force the rf either onto the mast itself, or to remain upon the coax only for the 18' length. Unless I am missing something, you are effectively providing a radial system for this antenna without either isolating it from mast nor providing additional radials.
I want to be sure of this so your method can be duplicated for potential usefulness by others in a similar situation.
This is similar to what I do with the Astroplane. I advised one fellow to do this with his AP, he did not and suffered from CMC. This past Monday I helped another set up his AP at an identical height in an even more populated area. I put the coax choke 1/4 wavelength down the mast and he has had zero CMC complaints so far.
Have I understood you correctly?
Thanks
Homer

 

[bob85]

eddie,
you seem to have a problem remembering what i said about 1/2wave lines,

an electrical halfwave of coax repeats its terminating impedance at the input end of the coax,

the electrical 1/2wave is determined by the velocity factor of the inside of the line,

an electrical 1/2wave line is shorter than a line that is 1/2wave multiples on the outside of the line where cm currents flow,

ergo, cutting 1/2wave electrical lines avoids making the line exactly 1/2wave mulitiples on the outside of the braid,

what is a bad length for the outer braid depends on it been grounded or not grounded and inverts accordingly,


homer,
you understood / described perfectly what i had my ham buddy try,
it worked for him, your mileage may vary

 

[Needle Bender]

Bob, a choke at 18' below the A99/Imax feed seems like it would create an inverted current mirror image of the antenna below it on the shield and mast, did doing so affect signal performance in either a positive or negative aspect?

How far below the 18' mast did you add in the choke?

Marconi, Have you ever tried modeling the A99 with 1/2 wave horizontal radials?