Different installations of the Imax antenna at different heights.

[Marconi]

BBB, can you describe or post a picture of the back of your HyGain Co-Phase box. Do the instructions tell you to use a specific length of coax from each antenna to the box?

I have done such a test here just using random feed lines connected to a 3-port "T" connector...and I saw no difference on receive over just using a single antenna as best I could tell, and the guys I talked to on this setup said my signal looked the same. I didn't expect the setup to work Pre-mo, but I figured if it worked at all and was not right...I might here from other operators "...I see your signal getting worse, and that didn't happen either.

If you've used this before...tell us how it worked, and could you really tell a difference?

 

[Marconi]

DB, I went back and checked your first post on the capacitor modeling ideas you have. I saw where the Imax I used was not very similar to the results you got for your "reference antenna." I did change my segment settings, however.

So, I messed with my model and noticed that the radiator lengths were noticeable different. IMO I think your radiator length is too long for a real Imax2K.

Your Ground Description was not the same as mine using "Average Earth" either, so I change my model to 0.002 / 10, and that got me closer. This Ground switch could still be off a bit, and maybe I have to go to 0.001 / 5, but we'll see. At times you have told us what you used for your Ground Description, and that was always useful for me.

If you would post your main screen with your models...that would probably answer a lot of questions I might have too. When Henry was still talking to me, he used to ask me to do the same all the time, show the descriptions or the Average Gain. I agreed with him, the information was very informative for me. An antenna image is also useful and might help me not to be asking so many questions.

Just to be sure, I would like to know what radiator length and diameter you used? My radiator is only 268.5" x .0625" inches and IMO that is the exact length of the real Imax 2K radiating wire element from the top down to the middle of the brass capacitor.

IMO the 16" inches starting at the bottom of SO239, at the base mount, to the middle of the brass capacitor in the Imax is for matching, and the radiator wire starts at the top of the middle portion of the brass tuning capacitor noted in the schematic.

Click here for source of images only: http://www.copperelectronics.com/cgi-bin/discus4/discus.cgi

So, don't bother to go back and respond to any of my old questions, I've figured out most of what our differences were. At least I have my reference model pretty close to your reference model.

I'm waiting for part 2, bud.

It is Christmas time DB, you ought to be taking some time off...I'm on holiday with a couple of months off.

 

[Marconi]

DB, I also find when I tested my new reference model in Free Space using your capacitor the Average Gain is 0.991= - 0.04db, and the gain an angle are much better than a regular Imax model with no capacitor included. That is very surprising to me and this gives me an all new regard for the Imax...if the bad match it produces when adding the capacitor doesn't wipe out the nice gain advantage I see.

I might ask if you add your 4Nec2 matching feature to your model without the capacitor, does it make a noticeable difference in gain vs the no match model?

If not, then it looks to me like adding this capacitor offers a noticeable benefit while adding matching using the matching feature in 4Nec2 does not show any benefit to our models. Of course, it makes the match and SWR look a better when you add the matching feature.

So if I'm right, and you added matching to fix the terrible match caused by the addition of the capacitor...I predict the gain and angle will remain the same o same o.

I got that Imax new in the box from a buddy that moved and could not use it. He just gave it to me one day. I never did test my Imax much...I didn't like its response compared to my A99 the first time I had it up. That said, I'm not sure I ever mounted it with new or good coax. That could have made all the difference. I just never thought about it until the other day. I know several guys that had an Imax, and they always made a big signal and they really talked DX good.

DB, you did it again. Thanks

 

[Henry HPSD]

(just to clarify...)

@ Marconi...

If you would post your main screen with your models...that would probably answer a lot of questions I might have too. When Henry was still talking to me, he used to ask me to do the same all the time, show the descriptions or the Average Gain. I agreed with him, the information was very informative for me. An antenna image is also useful and might help me not to be asking so many questions.

Don't get it wrong.... I don't recall that i have mentioned im not talking to you.
You asked my point of view so I gave...
Its fair enough that you dont agree with me, Im happy with that.
I haven't been on a lot due to work...and i probably wont... Actually i have no idea where that other topic went to, i might catch up during the hollidays.
However: if needed...you (guys) know where to find me I

So, dont get the wrong idea Eddie ...afterall those hollidays are comming up

 

[Marconi]

Merry Christmas Henry.

You told me once that you were not interested in hearing the personal stories about what went on during my experience, fussing and discussing the Sigma IV antenna ideas with the usual suspects here on the WWDX CB forum.

You also asked me not to post my ideas about the Sigma IV as well. But I told you then...to go to hell.

So don't waste my time, I'm not interested in hearing your personal experiences either. he he

 

[Henry HPSD]

As mentioned :

I never said I wouldnt talk to you...

Your response is rather amazing.... and I dont see how that replies to the context.

Why would you respond like that ?
What have i done wrong to you (or others?)
I dont remember you telling me to go to the H location ? etc..
But if you did, i must have missed it.

Though, i find that hard to believe as I know myself a bit and have seen enough not to be if people start doing that...
I wont put any effort in it anymore as its not bringing anthing meaningfull.

You are correct that im not interested in personal things, (like the above.)
Simply cause...well ... I dont see in what way it could contribute ?
All those stories about all who is bad, Im simply not interested...

Facts Marconi...not assumptions dont think you are correct.you need to know....facts..

Its a wast of time to read things like this.
There just are far more interesting things to do, and far more interesting things to learn.
For what it is worth: Im dissapointed for the time and effort i have spend in order to help.

But dont worry, i wont be around to much...if all
With the main reason things like the above...

And if you truly have anything to say to me, contact me ...i wont read this thread any further.

With that said, i truly do wish you all the best.

Regards,

H.

 

[Marconi]

Bye

 

[bob85]

Eddie
When you model white sticks like imax remember that the physical length of the radiator in the real imax is shorter than a piece of wire of the same electrical length in air due to the dielectric constant of what surrounds the real radiator been lower than air.

We don't know the dielectric constant so some precision guesswork is needed.

 

[Marconi]

Eddie
When you model white sticks like imax remember that the physical length of the radiator in the real imax is shorter than a piece of wire of the same electrical length in air due to the dielectric constant of what surrounds the real radiator been lower than air.

We don't know the dielectric constant so some precision guesswork is needed.

Bob, a good point.

I can't argue one way or another but I think, I and others have argued what the real physical length of the Imax radiating element really is, and nobody has even mentioned the use or consideration of the random coverings in models.

Most don't agree how long the actual physical radiating wire is, forget the effects of the random. My models are almost always shorter if I'm able to tell what another has done in that regard.

I don't do a good job with meanings sometimes, but I can follow instructions on actual dimensions most of the time. If you were to model an Imax what wire length in inches would you use... considering the points you make?

 

[bob85]

Imho the radiator starts level with the top of the coupling cap outer brass tube and ends at the tip

I don't know much the radome shortens the imax,

If i remember correctly Its not just a fiberglass tube. theres internal support like semi air spaced coax uses and fat brass joints electrically lengthening the thin wire radiator a little.

 

[Marconi]

Do you think 1" inch shorter radiator might have a proportional effect as we might see if we include the random and the 2 fat brass joints to this model?

If so, 1" shorter makes 0.01 dbi difference on my reference model which I set to the physical length where I measured on the antenna itself. The only difference I measured is...I started at the middle of the brass capacitor where I think the wire from below and the wire from above come very close to connecting buried in the insulator on each end. This idea is very similar to what we see in the image of the schematic I posted above in the article, entitled "The Imax 2000 Exposed?" There you can clearly see the wires are embedded at the internal end of the insulators within the capacitor near the middle it seems to me.

My measurement is <>1" inch shorter than you described and this difference increased the gain of 0.01 dbi. Two inches shorter made an increase in gain of 0.02 dbi difference. So, in this instance shorter is better for gain.

I have seen models that set the length of the Imax at 292" inches and say it is according to the specs...showing 24' 4" inches. No wonder some claim this antenna is a .64 wave, but I'm not sure that is even close to correct for a .64 wave.

I know it is way too long, though. A model of an Imax radiator that long will raise the maximum radiated angle up to 45* degrees according to my model.

Hello 1/4 wave GP.

 

[Marconi]

Bob, sorry I got off track in another discussion.

I've been wanting to ask you to recall this post to me from another thread on the Imax? What you say here still holds true, but you got me to thinking.

IMAX 2000 continuity query

You know that puzzled me for a whole day when I was trying to track what DB was seeing with his new Imax idea with a capacitor added. You talked about common sense. It didn't make sense to me why the Imax would have gone that bad with the match...just adding a capacitor to the center.

I also spent parts of several days modeling and trying stuff that would get me closer to his results...but to little avail.

I finally decided to go ahead and post my results even though I would be disagreeing with his results again. That never works out well for me, but I do get to be the bad guy in the Antenna Section of the forum for a while.

Well, the reason he saw a very high end-impedance was because he had his Imax radiator length set at a bit over 23' feet. I estimated from my own fiddling around with results that he set his Imax at about 278" inches tall. My model was showing me around 500 ohms or less...with the length dimensions I used, right or wrong.

Isn't this a similar issue to what you just raised above...regarding the Imax having a random and two large lugs in the wire to deal with in modeling white stick antennas?

IMHO this...is why our models did not agree more closely when I first posted my models trying to show similar patterns as he was seeing.

DB, I have another question or maybe I've already asked you early on in this discussion.

How say you?

 

[bob85]

I don't expect small changes in length to cause anything more than the small change in gain you noted in your model Eddie.
We have coverd the .64wave smokes a 5/8 voodoo several times in the past.

The imax could be close to .64wave. I dont know the exact length or how much the radome electrically lengthens it.

I would not argue with your idea it starts at the bottom of the upper brass spark gap rod inside the tube (electrically).

I expect electrical length with or without radome & ferrules will have more effect on impedance and resonance.

Something i noticed on your 2 x 1/2wave model is you have significant current at the tips of the antenna.
A place where impedance & voltage are very high. Current is very low.
Then i remember eznec samples in the center of a segment not at the ends.

Does that mean that the more segments you use the closer the currents and end impedance will be to the real antenna ?

Do you and DB's software sample in the same manner ?

 

[Mudduckmobile]

There are three ways I've seen it done. The old way that I don't recommend anymore involves insulating the mast from the antenna hardware. We started with electrical tape, you want to use enough that there is minimal capacitance between the mast and the mounting brackets, so more is better, as long as you can fit the hardware around the electrical tape. Unlike a magnet mount antenna, you want as little capacitive coupling as possible. One person found a rubber sleeve that just fit over the mast, and inside the mounting hardware. It was a tight fit but it worked. I suppose if you have a dense piece of rubber you can wrap that around for the same effect as well. Might be worth looking at some of the flat floor mats used in cars if they still make them, although they might be to thick...

I mentioned above a 1 inch fiberglass rod. You bolt the rod to the mast, and the antenna to the other side of the rod. A two foot rod is generally enough. Depending on where you get them from they can be somewhat expensive. I will generally paint them to help prevent UV from the sun wearing out the rod to quick.

Much more recently, and still being experimented with, we have used one of the half inch diameter high density cookie sheets. We cut it to size, and use clamps to bolt it to both the mast and the antenna with separate but close hardware. So far the two I have seen done this way are holding up well, although I want to give it a little more time before giving it my seal of approval. It is cheaper in general than using a fiberglass rod, and I paint these for the same reason as I paint the fiberglass rods...


The DB

A bit of INTER TUBE from a truck or a "thorn prof" tube from a bike works real good, just cut a bit out and wrap around the mast zip tie's work to hold it in place tell you put the antenna mount on.

 

[Marconi]

Something i noticed on your 2x 1/2wave model is you have significant current at the tips of the antenna.
A place where impedance & voltage are very high. Current is very low.

Are you talking about this model possibly from another thread?


Bob, after I posted that model, I think in another thread, I tried to match it and it has changed as a result.

I just posted that image to try and demonstrate what the 2 x 1/2 waves you and NB were discussing might look like for him. I added the Currents Log to help demonstrate the in-phase issues and balance or lack of balance at the feed point...which I thought might be at the center of your claim to HB.

At that time I had only a feed point in the middle, and I have no idea what other settings I might have had. In fact I deleted the model and had to retrieve it from my Trash Bin.

I'm sorry I didn't make a project of that model and check the details out fully, so maybe I could answer why it showed a rather large current >.50(A) at the tips.

A good point Bob.

I haven't figured it out yet. I'm just not sure. The model has changed. What do you think could do that?