Base Working on a 1/2 wave J-Pole

bob85 said:

Eddie,
i will take the 8.9db version, when will mine be ready ?

If its that easy to fake models what do we look for to check the model has been done correctly,
if there's no indicator its been fudged people can claim anything they like.

Click to expand...

Marconi said:

Bob I'm working on a J-Pole model right now.

I don't know Bob. I reported what I saw that looked questionable earlier that got my attention...but no body responded, so I did not elaborate further. I just kept on trying to get the model to show better results, but it was no-way-no. Ask yourself..."...self what is my opinion on the words, about performance, from folks that manufacture, promote, and sell the CB antennas?"

Click to expand...

Bob, as I mentioned a while back when we were discussing the Vortex model......"I was working on a 1/2 wave J-Pole."

You're right, folks can say or claim whatever they wish. We just have to make some judgments in life about what folks say and mean. Like I've said before, "...you can often tell what's in a man's heart by his fruits," a good idea I have taken from St. Matthew 7, 16-19.

Hear is the J-Pole model, based on some old dimensions given me by an old buddy that use to build these out of Copper. He also built an Astro Plane and StarDuster replicas.

bob85 said:

That looks nice and symmetrical Eddie,
i expected more skewing from the bit of radiation you get from the stub.

Click to expand...

The antenna view posted earlier was looking in the direction broadside to the X coordinate and the model below is looking at the Y coordinate.

bob85 said:

That's more like what i expected Eddie,
you demonstrated another way a model could be somewhat deceptive if all the info is not included or the audience is not paying attention.

Click to expand...

Yea Bob, IMO this is what skewing is all about. Every time we see an ad we're seeing a deceptive way of looking at products to some degree or another. Modeling is not the deception here...it is the man behind the model...whether due to oversight or intent.

Folks a lot smarter that us...were behind MOM design and implementation ideas.

I mentioned above that I was working on a J-Pole project and I was studying everything I could find in my files on the subject from the past. I remembered reading something on this subject of skewing...so I took the chance I kept some references in my files.

Below is that reference from CQ Magazine. Check out Fig 2. The author is talking about this issue back before March of 1998. Also note the references in the Footnotes at the end of the article and you will see a familiar contributor to the science.

This link might also be of interest to you Bob. The author noted above is an old reference you've used in the past,..Dan Richardson, K6MHE.
http://forums.qrz.com/index.php?threads/avanti-sigma-vi.289143/

Bob, here are some overlays of several vertical CB antennas of note...that I compared. Here again, the (*) beside the antenna model's title indicates the active model. I did not verify each model against a Free Space model, perse, but all of the models are dated here, and during this time I was making sure my models had a good Average Gain result in Free Space...before setting the model to Real World with losses added.

Here again, we see very little performance differences...something I've claimed for years...that I was seeing in my real world comparison work on some of these same antennas, albeit my ideas of A - B testing were considered by most experts here...as no-way-no.

Bob, these overlays show us again that you are right...the Vector shows the most gain. All models are at 36' feet to the feed point.

Personally, I'm not sure anybody has ever been convinced by these models, but I think modeling has dispelled some old CBBS ideas of the past.

bob85 said:

if im testing antennas with fairly low loss matching & no cmc issues i don't expect much difference when mounted at the same tip height,

Click to expand...

Good idea and you maybe right on the mark, even though in my personal real world testing I could not sense an obvious and notable difference. When I did see differences, which were few and far between...I chalked them up to anomalies I could not duplicate or understand.

I will try some models that test that specific idea.

bob85 said:

mounted on the same mast its a different story, especially when the extra height of a longer antenna means current maxima is higher above ground and more of the antenna is above obstructions.

Click to expand...

Bob, I agree with this idea too.

However, long ago when I first reported seeing little difference in the way my CB vertical antennas performed...I had little to no idea about all these extenuating factors and how they effected antenna performance for sure. This is when I bought my I-10K to compare to my other antennas...which were all noted NOT to be high gain type antennas.

I remember years ago, a group of guys hereabouts would talk about such things as CMC messing up antenna patterns and interfering with other household electronics...but later it tuned out the group claimed to be ham operators. When a few of the local guys I knew would try and talk to them...the flaming started...and I had no interest in fighting that battle on the radio.

When I posted a few videos and guys could see what I was doing...I heard all the concerns for my A-B testing. But for me, at the time, I got that old feeling...the flaming was starting again and sometimes it got pretty bad...here on the forum as you well know.

I now take a different view for the things I did not understand at the time, and a lot of that is a result of my getting into modeling. In spite of a lot of issues about modeling having limitations and Eznec and modeling being junk science...this is where I felt maybe I could actually test some of the ideas in spite of all the complaints.

That said, I suspect today there is just not much interest in such details at best...for a difficult program to master and try and understand.

bob85 said:

That throws my old tests into question as mast & coax could have been effecting my results, the same applies to anybody elses tests that did not isolate the mast & feedline,
take my imax vs i-10k test, the 10k blew the imax away to reliable people, i think cmc ruined the imax pattern but not so much the 10k,

Click to expand...

Are you suggesting there was a time when you did not realize that you had a CMC issue? I know that happened to me. When I found out different...I started watching, and except for the worst case scenarios...I still could not tell much of a difference and for sure in every case. The few test I made back then seldom proved to be repeatable and my Signal Reports did not seem to reveal much either.

Then we hear the Elmer's making big sounding claims of benefits in one sentence and in another they will tell us that making remedies for CMC's that don't work...can also make matters worse. Bob in this later situation, how do we know for sure the remedy works but instead is just making matters worse?

bob85 said:

if its important to include them in models its because it can skew the results,

Click to expand...

In most models adding the mast can make a difference in several ways. In other models adding a mast does not seem to make much if any difference. In other situations simply isolating a mast might not help either, and in some cases a mast is part of the antenna itself and the model does not work in Free Space or over Real Earth if not included. IMO, one rule does not cover all these situations.

I figure the Elmers are just giving us a simple heads up that modeling for antenna performance requires through verification (Average Gain Test) and a watchful eye on the many details. And they don't wish to get too complicated in their words trying to explain this stuff about CMC, and sometimes not much else for that matter.

I'm pretty close to claiming that a model needing a matching device also needs something in the model that mitigates the mismatch, and the Plain Jane model (less the matching) will not show close to accurate results. I have to admit I have made many Plain Jane models that were not accurate.

I'm also inclined to claim another thing here Bob...we seldom see any modeling that requires a matching device and is obviously included in the models. I am curious and have to ask WHY!

Maybe one day I will know for sure if I'm right to make such claims.

bob85 said:

i think the efficiency of the matching device will play some part & some antennas will be more prone to cmc issues than other designs,
don't know how much or how you accurately model something like a silver rod or clr2 with the farty little pcb coil.

Click to expand...

Bob, I too have seen noticeable differences in the effects of what I would call CMC's on the feed line or mast for some of my models. FWIU, these differences are likely due CMC's.

In some of my models these currents sometimes appear constructive to the performance and in others the effects appear destructive. I have heard that CMC's are always bad, but long ago I talked to an engineer at Solarcon and he said in some cases these CM currents appear to produce more gain depending on the phase relative to the radiator. He said it is not always easy to tell when working your radio. My personal experience also suggest the same thing...so I tend to believe his words.

I've realized CMC's on some antennas at my station, but in those cases I only made an assumption, because they were creating obvious TVI type interference at my shack or neighbors complained. I don't know about some matching devices being the culprit, but I know for sure that proximity has an effect, so I do try and get my antennas up high. Base on my modeling I see some CMC currents appearing to be constructive, so if I was out in the country and nobody close by like it is here in the city...I might not ever realize the antenna was acting better or worse unless my shack showed some symptoms. This is not to suggest that an antenna with CMC is not important, but how would we know for sure.

You mention how I(we) accurately model some antennas with unique matching devices. Bob, it is a fact that I don't know how to simulate a physical matching device for some of the antennas I've attempted to model.

For example I was having trouble with the hub on my AstroPlane models. I was trying to make the hub appear as I saw it in real life. DB showed us a simple method using two short wires in place of the large hub I used...and that was the difference that got me beyond my mental block on the issue.

DB also tells us that GHZ24 showed him a trick to help control the Average Gain Results, and in many cases that works. Both modeling programs we use, Eznec and 4Nec2, have a simple method to determine the accuracy of a model using the Free Space result for Average Gain even when we can't "dial a model in." IMO, both results are good enough for Government work.

The models below attempt to show how this works.

Notice the 1st page below is the Eznec Control Center screen. If the model is done in Free Space and all the losses are turned off...the model will report Average Gain...noted at the bottom of the screen. This value can be more or less than the value of "1" <>. Example: 0.980 or 1.020 is consider as an accurate range in the Eznec manual, but the value of "1" is best.

This is not the only value noted with the AG result however. There is also a value noted as a correction value. This value shows as prefix of " - or +" with a value following. The "-" value can be added to the models gain results noted in the Pattern View, and the "+" value is subtracted from the models gain results noted in the Pattern View. This corrects the gain for a model that does not show a good AGT result.

This correction factor, when adjusted, allows the modeler to use the results calculated as though the AG test showed a perfect values of "1" This way DB and I don't have to use the "dialing in "to differentiate" process to make the gain as close to accurate as possible. That said however, the model sure does look better if the gain is not "over/under" stated due to an error in Average Gain.

The models below attempt to demonstrate this idea.

1. shows a model with an AG = 1.182 and a correction factor of +0.73 in Free Space. This means the model is not very accurate and the gain noted on the Pattern View is over stated at 2.82 dbi.

2.82 - 0.73 = 2.09 dbi when corrected.

2. shows the model "dialed in" showing an AGT = 1.001 db with the gain noted on the Pattern View page = 2.10 dbi as corrected.

So, if we have a model that we can't "dial in" or can't model with some type of matching so easily...we can use the correction factor the software provides and see the gain results corrected as though the Average Gain = 1.

So see Bob, these programs have limitations, but pop up widows tell us when we exceed the limitations and even give the dimensions to correct in some cases. There are other examples of limitations that also popup with warnings and information to help correct.

Bob, you may have already got a grasp on this process, but here it is again...just in case. I hope this explanation is understandable and if it's not...DB can surely clear it up.

Henry HPSD said:

And i read a couple times "tricks"to show a good average gain value..

Those "tricks"... for whom are they ? I dont like tricks....so it triggers me..

(in other words...are they used to trick the software ...so you see what you want to see ?) Or ...is it really helping to improve the software..

(possible u already described it..im sorry..just shouting out loud to what im reading i haven't dont a deep investigative reading...maybe tomorrow.....it just comes up ..hope u dont mind.

Henry 19DX348

Click to expand...

Henry, both you and The DB have taken exception to my use of the word "trick" when talking to DB about what he meant...when he told us his story about GHZ24's giving him a heads-up on a way to manage the Average Gain Test to get real close or equal to "1."

I never planned to talk about this again Henry, but I felt now is the time to let the truth on this matter prevail.

I was not the one that first used the word "trick" in this regard.

Below is the source that I referenced when I first heard about a "trick" from GHZ24 to achieve a perfect AGT = 1.

I don't mind, I didn't do anything wrong.

Any Astro Plane Fans ?