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THE UGLY BALUN choke

Since it is an experiment to see the coax being affected; then you should probably use a 10 ft fiberglass section at the top of your mast - so that the antenna will use the coax and not the mast as a ground plane.

Would you agree?

That might be a good idea Robb, because as I understand this...anything attached to the feed point has the potential to flow currents.

But, how many stories have we heard where isolation was not considered and a choke alone was successful in solving the issue?

What if we do a choke and don't isolate, and find out a choke does minimize CMC enough that symptoms stop. But if we check closer in the process we figure out we could have just increased the feed line the same total length as the choke, and the problem still went away.
There are lots of videos on YouTube that are about chokes, check them out and see how many discuss isolation.

Is this maybe what these guys showed as a good result, but really didn't figure out why...just thought it as fixed because of their choke?
 
If the antenna is mounted to the mast and has a rf choke installed; then the choke would have no effect on the CMC - because the CMC will still pass over the mast.

However if the antenna is isolated from the mast by using a fiberglass section greater than 1/4 in length; then the antenna would probably benefit from full-length radials and a rf choke. Although the user may/may not notice a difference in TX/RX, my guess is that the polar pattern would be better organized and have very little CMC. But who bothers to go to such lengths; and at what additional cost? It should work better; but a signal strength meter and an operator that can use it right would be the real test to determine validity.
 
If the antenna is mounted to the mast and has a rf choke installed; then the choke would have no effect on the CMC - because the CMC will still pass over the mast.

However if the antenna is isolated from the mast by using a fiberglass section greater than 1/4 in length; then the antenna would probably benefit from full-length radials and a rf choke. Although the user may/may not notice a difference in TX/RX, my guess is that the polar pattern would be better organized and have very little CMC. But who bothers to go to such lengths; and at what additional cost? It should work better; but a signal strength meter and an operator that can use it right would be the real test to determine validity.

Robb, that sounds like a good idea, assuming you are right that the choke would have no effect on CMC.

I would try that using Eznec, but I can't model a choke at this point. It might be interesting to see what happens with your idea up to the point of adding the choke however.

What particular antenna would you consider using for this idea Robb?
 
The A99; thought that was the test subject.

EZNEC would be OK. However, I don't think it could simulate the fiberglass pole for attaching the antenna or the rf choke. Can it?

Radials may/may not need to be drooped for reaching maximum pattern optimization and perhaps impedance - as well.
 
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The A99; thought that was the test subject.

EZNEC would be OK. However, I don't think it could simulate the fiberglass pole for attaching the antenna or the rf choke. Can it?

Radials may/may not need to be drooped for reaching maximum pattern optimization and perhaps impedance - as well.

I agree and I just happen to have a series of 1/2 wave radiators with different radial/no radial setups. This was done to compare how similar they all are considering that they can work without radials. You can see in these models that none suggest a big imblance in currents with the mast as noted by the red lines for currents.

At a different antenna height, or as in this case a different feed line length these red line currents may differ.

I just added one showing an isolated (ISO) noted with a 1' foot length insulator. This insulator is represented by a 1' space. If you would like to see what this would look like with a 9' space, then let me know. You may also find these are similar to my post #28 earlier.

There is an overlay of all these models on top.

View attachment .50w various setups..pdf
 
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I looked at those files - thnx. Not much lobe differences - as you said. But EZNEC didn't show a change in the amount of CMC on the coax - of course. However, the EZNEC did show more gain with the antenna that had the sloped radials. This could well be because the radials got the wave and not the mast that would have become CMC.

Soooo . . . Angled radials, an rf choke (for 'cleanup'), and an isolated mast for the A99 may well benefit performance - IMO . . . The rf choke might even force more current on the radials and away from the coax/mast and perhaps add a very small amount of gain.
 
Well Robb, you're right. The models do indicate the slanted down radials are best.

I guess my point that I see little to no difference when I test these ideas in the real world just using my radio...was wrong.
 
eddie
i know you don't think the difference noted in your models would be detectable on an average radio,

i don't see how you have currents on the mast if its isolated, do you have coax in the models too?

try modeling a 1/2wave on a mast not connected to ground using a mast of odd 1/4wave multiples, or use a 1/2w multiple mast connected to ground so you have a low cm impedance,
i thought you did this before and posted reults but im not sure.
 
eddie
i know you don't think the difference noted in your models would be detectable on an average radio,

i don't see how you have currents on the mast if its isolated, do you have coax in the models too?

try modeling a 1/2wave on a mast not connected to ground using a mast of odd 1/4wave multiples, or use a 1/2w multiple mast connected to ground so you have a low cm impedance,
i thought you did this before and posted reults but im not sure.

No feed line on the models Bob. I can only guess right now, but I don't think I've ever see an isolated mast that I've modeled that was totally void of some currents. Usually, the red lines for currents don't show up on such models, so I never thought much about it. I'm just curious, do you think the mast on such a model should be totally clear of any currents?

I think I just picked this model at 48' at random, and did all the iterations on this single model. I do this to help me make sure I've used the same model, and make changes to it.

I see what your saying, and I don't know. It looks like the current for that model is starting it's current at the top of the mast and not at the bottom of the radiator or the feed point which is the red circle. I've never noticed that before, and I don't understand it.

I just added that model to the others, because Robb wanted to see an isolated model.

I also note that the type set for the caption for that model also changed the from the others, and I did not change that.

I'll have to get back to you guys on this one, it has me stumped.
 
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I found out what I did that caused the model to look strange. The model was set for inches, and when I made the adjustment to isolate the mast I was thinking I would set it at 1' foot shorter and isolate it. I made it 1 shorter and that only achieved a 1" inch clearance instead of 1' foot.

When I fixed it to 1' foot, the model no longer showed the currents seeming to be touching the top of the mast, however a little current still remained flowing on the mast as you noted earlier.

It was pretty strong near the ground, but not strong at all near the top of the mast. I isolated the mast from the ground about a foot too, and the mast showed even less current flow as I recall.

I also made the isolation 102", like Robb suggested, and I think the current on the mast got lower still, even though such an effort may really be risky.

I was playing with this setup some more at 9' foot at the top and 1' foot at the bottom, and I found I could eliminate much of the remaining currents just by using a 12"- 18" inch radial at the bottom of the radiator, and still maintain the gain and angle. I'm not sure yet, but maybe that is suggesting that Yates is right, it doesn't take much radial length to establish the necessary current return path and decoupling talked about. I am convinced now that radial(s) will aid in decoupling this antenna somewhat. Even so, it doesn't look to make a big difference in the results according to this model.

Bob, you're probably right though, maybe your radio would indicate this small amount of change. At least your idea sounds reasonable to me, even though I don't think I've ever seen such a difference on any of my radios. If I had, you can be sure I would not be saying I tend to see all my antennas doing about the same if they are even close to being near a similar current maximum in height.

I'll check all this over tomorrow. I'm tired.
 
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i don't think i could see the small change shown your 1/2wave models eddie, not even using my fluke as a meter, there does not look to be enough mast current to cause high angle radiation,
creating a low cm impedance mast length may show more current,
i have seen the claim that a 5/8wave is worse than a 1/2wave for mast currents, i don't see anything in your models that argues against that with the mast length you chose for the models.
 
... induction, or induced currents due to proximity. Absolutely normal.
- 'Doc

'Doc, I hope you're not close to all the bad weather up in your area. On TV these pictures are devastating.

I think you're right, it is induction and it is probably pretty normal with vertical antennas and the mast. It is discussed a little in the Eznec Manual at Page 56-57, where feedlines and Baluns are discussed.

No telling what these near field currents do or look like. I don't think I've read anything detailed on the issue either. I'll have to check the Eznec manual further and see if this is discussed.

This error of 11" inches has opened up a whole new area for me in modeling, and it is pretty confusing what I think I'm seeing.
 
i don't think i could see the small change shown your 1/2wave models eddie, not even using my fluke as a meter, there does not look to be enough mast current to cause high angle radiation,
creating a low cm impedance mast length may show more current,
i have seen the claim that a 5/8wave is worse than a 1/2wave for mast currents, i don't see anything in your models that argues against that with the mast length you chose for the models.

Bob, I agree the currents on these masts look very low and thus probably won't cause increased high angle radiation or CMC's that might cause some problems.

I know you understand when I do models I always risk doing something wrong, either a stupid mistake and I know better, or leave something out, or I make a mistake due to not understanding enough. Some would say, those issues should stop what I try to do.

I find myself pushing a lot of buttons in this project, and I need to slow down, but below are some of my follow-ups with some of what I think you're curious about.

I had a feeling I might have been hasty in saying that I could almost eliminate the currents on the mast with a 12"-18" radial, so I did this again. Maybe that is only true if the mast is isolated (ISO) at both ends, the ground and the antenna. Right now I'm not sure.

I did discovered this AM that I may be getting somewhat confused in doing some of these iterations with the models.

At this point though I think the gist of my thinking is still viable. There does not appear to be much I can do with radials or no radials on a 1/2 wave radiator that seems to make a critical difference in gain or angle. I keep coming back to the same indications with these models.

I'm not even trying to track the match in all of these models to see how it is effected...albeit these EFHW models are no where near matched.

However, my experiences in Eznec tends to suggest to me that the match is not that important to the typical results we look for or expect, but I still do it, and still I wonder...because sometimes we just never know for sure.

I will add that Homer did some checking with an EFHW 1/2w he had built along the ideas I had suggested to him. This was regarding checking to see if the match changed for him during a series of modifications to the antenna... similar to what I'm doing here, adding radials, and what I had previous done in some real world testing I did sometime back.

If I recall correctly he recorded similar results to my own real world testing using the idea, and what those models tended to show...was not much changes on an end fed 1/2 wave radiator whether he added radials or not. I didn't do slanted radials here in these models, but I did in my RW testing. I think Homer might have done something similar in his testing.

Sure I see some differences and so did Homer, but in the whole they were very small differences, and maybe they don't even matter with guys that have radios like mine...that can't really detect a small difference as we see here in these models. You and I have talked about that before.

I've also scoured YouTube for videos of guys comparing signals, and for the most part I see guys reporting small changes on switching antennas, and talking about needle width differences as well.

So, I just don't know what else to try and do.

Sorry I didn't do the ideas for a 1/2 wavelength or odd 1/4 wavelength feed lines and mast yet, but when I unwind a bit, I will try that idea and post it... whatever it shows.

Here is some stuff I just did checking what I did last night. It is mostly adding a feed line to the models, but again...not much changing in the gain and angle.

View attachment Bob's discussion on the .50w.pdf

I also added the Tabular Currents Reports so you can try and check how the currents change in these models. Let me advise that this log shows the currents at segment 1 first. That is the bottom of the radiator and the last segment is the tip. So not to be confusing, they are upside down.

I also added some notes to point to the areas I tend to watch on the wire segments listed. I expect to see bigger currents in the middle area of a 1/2 wave radiator and near zero on both ends. I expect to see big currents at the base of 1/4 wave radials, and near zero at the tips. The same is true for a 1/4 wave radiator. You might also compare the max current at the segment on the radiators as well. This current is what I understand makes the maximum signal.

On a 1/4 wave I also expect that if I sum the currents for the first segment for each radial, that the result will be approximately what the current is on the first segment of the radiator. If it is not, then the resulting difference will most likely flow over onto the shield of the feed line/mast and back to ground as it touches the Earth ground where ever it terminates. As we know, it is the magnitude of those currents that matters concerning CMC's.

These are not facts, it is just my opinion on things noted here.
 
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i only saw a few needle-widths change when comparing the gainmaster to my i-10k to everybody but one friend who noted if i recall correctly a couple of s-points drop when i swapped from the 10k to the gainmaster and back up again when i swapped back on his ft897 meter,
between imax and 10k we had 1.5 s-units to one guy and more to another friend,
i put it down to the imax not been happy on the same pole as the i-10k, not that the 10k had that much more gain,

if you can't make cm currents look bad with any length mast or feedline i don't know whats going on with the model, i know you can have enough current on the coax to cause bad rfi in the shack with an a99, isolating and adding radials cured it, the same is true with the imax.
 

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