When it comes to modeling, a deep study of chokes is on my list of things to do. From a post I made above...
I once did some modeling examining choke locations and cmc's flowing on feed lines/masts, I think it was for Homerbb. It was far from complete, and I have gotten some new ideas to try since then, such as the 1/4 wavelength stub on the mast idea mentioned above, and shown in one form or another on this forum recently. I just haven't had the time lately, but it is something I intend to do at some point.
I have made statements on chokes multiple times, and have talked about this to some small extent, typically when someone links to one of K3DAV's web page of mis-information. The one in question is where he says any coil of wire in a coax will act like a choke. This is not true in his case, and it is not true in your case.
It has occurred to me that we might be defining what a choke is differently. When it comes to what I consider a choke I limit myself to devices that I can take unaltered and apply it to all antennas of the same frequency, and get the same result. I do not believe that you can say for certain that that will happen in the case you have pictures of above, although I am always happy to look at evidence to the contrary.
Let me be clear, I believe that you did have the experience you claim and it worked in that specific case as you have claimed. I have no reason to doubt this. I am sorry, however, but you cannot guarantee that with what you are picturing above, that you could remove it from this antenna setup and put it unaltered into any and every other antenna setup of the same frequency range and have it always have this effect. Because of this I cannot call it a choke, and in fact have to limit myself to to the possibility of this being a lucky occurrence. I caution you that I have actual experience of simply routing a coax differently causing a similar effect to what you experienced to happen, but you don't see me calling that a choke do you?
I don't recall seeing your modeling data on this, and I feel I must ask, did you try to duplicate a circumstance where adding such a device actually made a problem worse, or even created a problem?
I am going to ignore your naysayers comment. What a choke can and can't do is well defined, at least to me. Many many people have their own stories of things that they attribute to chokes that they have created that aren't actually chokes. So they put up an antenna and made a choke like device and didn't have common mode currents, good for them. At least in your case you had a problem that you fixed along the way, which is far more credible in my eyes. Also, be very careful about using that word, naysayer. More often than not it is used by people trying to put forth a myth they believe, and say people who have either a different experience or actual facts that doesn't tow their line don't know what they are talking about. It isn't very effective imho.
As I have stated recently, I have lost my collection of models, I don't have a j-pole or even
insert whatever antenna here model to grab and play with. I also don't think that I need modeling to explain every little thing, and what is and is not a choke is one of those things. If it is really that important to you then hopefully I will get to it eventually, after all see my quote of myself above.
I have modeled multiple chokes on an antenna before, but not on that model. It was, again, the previous work I did for HomerBB. I did make the statement that sometimes multiple chokes may be needed and I talked about when and why.
Somehow I missed one of your first remarks, namely about chokes being transparent. I agree and disagree with this wording based on specific cases. If their are no CMC's to begin with then the choke will be transparent. If their were lots of CMC's then the choke will definitely have an effect. If CMC's are somewhere in between then you will get a result that is somewhere in between. I think one of my previous comments could be interpreted to say something along the lines of being transparent, but it is definitely not what I meant. Their is a distinct difference between being transparent and not causing CMC's.
And finally, if you want more information regarding devices that I call chokes, then go
here. His chart is often linked on these forums, and if a good reference if you want to make a coax choke that you know for sure will work on certain frequencies. He also go on to what, why, and how he got this data.
The DB
