IMAX 2000 continuity query

[Marconi]

Here is my model of NM5K's last exhibit. It looks like Mark used a very old version of Eznec, but it hasn't changed much in nearly 17 years. The results are pretty darn close in my thinking. See, not much has really changed in NEC modeling except maybe for adding colors.

 

[Marconi]

DB, the PDF file below is what my model with the 42 pf capacitor added is predicting.

It shows us a nice improvement in the current distribution on the full length of the Imax radiator, Ok. But.............

My model with the cap added also shows a noticeable reduction in gain with an increase at a higher maximum radiation angle at 23 degrees vs. 8* degrees for the Imax with no capacitor.

We also see a noticeable increase and a shift to out-or-phase CMC on the mast. This shifts the mast/feed line from a constructive to a destructive RF contribution.

So, IMO this model is either in error or my adding this cap does not contribute to better performance for my model. I have no idea how all this is supposed to work in the Real World.

How say you?

 

[Needle Bender]

DB, the PDF file below is what my model with the 42 pf capacitor added is predicting.

It shows us a nice improvement in the current distribution on the full length of the Imax radiator, Ok. But.............

My model with the cap added also shows a noticeable reduction in gain with an increase at a higher maximum radiation angle at 23 degrees vs. 8* degrees for the Imax with no capacitor.

We also see a noticeable increase and a shift to out-or-phase CMC on the mast. This shifts the mast/feed line from a constructive to a destructive RF contribution.

So, IMO this model is either in error or my adding this cap does not contribute to better performance for my model. I have no idea how all this is supposed to work in the Real World.

How say you?

OK, it appears you have the cap a little too high up the radiator, and yes, The DB did mention that the placement & value is critical!

On his model showing mast currents it appears to offer a near full half wave of constructive current, and that's why I thought 1/2 wave downward sloping radials in the guy line might help to radiate only that constructive 1/2 wave of current, while also fully decoupling & isolating it from the mast.

I hope that's not too cryptic, I'm excessively tired tonight.

And on your 36' model with sloping radials, here's my parameters one more time for clarity sake;

41 feet at feed point, not 36'.
Steeper sloping 108" wire radials than your model's 45°( I'll claim 67°) attached to the bottom Imax2000 U-bolt (recently I mistakenly told someone the top U-bolt).

...and - I'd like to see the difference (at 41' to the base) of both an isolated & a non-isolated Imax 2000, including 1/4 wave steeply downward sloping radials, and perhaps even 2 other models employing 1/2 wave steeply downward sloping radials.

I sure hope that doesn't sound like a demand, I'm just so whoop'd tonight, "I might be sending my wife's grocery list". - Red ROctober

Ideally, if I were to erect one tomorrow, from my anecdotal experience,
I'd go fully isolated with about 3'- 4' of schedule 40 gray PVC, over 1" solid fiberglass rod - leaving about 12" - 18" of it exposed between the top of the mast and the bottom of the Imax mounting plate - so I'd have a generous area for wrapping a 5.5 Turn x 4" diameter PVC former coaxial Common Mode Current Choke over that non-metallic part of the supporting mast structure.

Then I'd steeply slope four - six 108" guy wire radials downward at ~65° angle from the bottom Imax U-bolt, making sure to install it at ~41' at the top of the mast / Imax mounting plate.

...whew, that was draining.
I'm toast, 73

 

[Needle Bender]

Well, except for the isolation aspect, that was my setup when it outperformed the Penetrator - a much beloved, arse-kicking, full size metal true 5/8, so I would've imagined it would be of great interest to model against just that, since my anecdotal experience even blew me away.
I'll come right out and say that it mirrored the +2dB over the Penetrator which I originally saw on the Gain Master, also at 41' at my other house.
I had never seen an Imax come close to performing as well as a Penetrator after numerous times of swapping &/or testing, so I simply just didn't believe my eyes and wrote it off to unknown oddities.
Since the new place appears it will provide some 140' trees for climbing & installing antennas, I'm now brain-farting on how to fiberglass up an Imax until it's roughly equivalent to a Station Master so it will better survive such an intense installation challenge, along with adding downward sloping 1/4 wave radials made from...???

I took this earlier today.



Alright, just awoke thirsty and now headed back to lala land, 73zzzzzzzzzzzzzzzzzzzzz

 

[Needle Bender]

I just found this, didn't realize it came out so well...



...that's the front yard.

I can already see the 80m Delta Loop

 

[Marconi]

That phase correction was enough to make two unexpected differences that, after I look at said models in more detail, seem to make sense.

DB, you once told me you were a math man, well I am a curious man...so you'll just have to forgive me my impatience, OK?

Can you tell us what you found, and how it made sense? I am interested in what you have to say and if we wait too long...you might be telling me I forgot, I have these ideas all wrong, and my thinking is apples and oranges again.

I knew there was a capacitor before this, and even where it was, it was 357 that actually got a measurement of said capacitor, and that made all the difference.

I can honestly say I've never heard anybody make such a claim, saying the Imax had a capacitor in its middle section until a while back.

357 what more do you know about this story?

All I can recall is thinking the object noted in the middle section was a noise damper, I personally checked it out on at least two occasions back in the days. Maybe I even posted something about those incidents, back then. I will do a search of my notes and on the forum.

DB did you ever talk about it when you found out the Imax had a capacitor as part of the antenna?

I actually tried many other values, and every value I tried at random had a big negative effect.

When I recently asked you what the value was, I made a note that you told me it was 25pf. I too chased my tail for a while like you tell us you did. I posted the other day that when I used 25 and a variety of other values...I could tell that something was happening and that the cap had an effect. I can only guess what effect the cap has, however. So I repeat...what is your opinion why Solarcon does this?

I will say that 1/4 wavelength radials should work better than 1/2 wavelength radials, for any number of reasons. You may have to remind me. I'll talk about those reasons when I get to that point if you are curious.

Based on the information that I posted for NB about the guy in my area posting an article on the Internet about his using 1/2 wave and longer radials slanted down on his Imax...I too am curious to know your opinions on this too...when you get time.

It is this part of this project in the link below, a possible collinear effect, that intrigues me.

click here: IMAX 2000 continuity query​

Like I think I've said already...I saw something similar to a collinear effect in the second Nec2 model you posted for this idea for a capacitor in the middle of section 2 on the Imax.

How say you?

 

[Needle Bender]

DB, you once told me you were a math man, well I am a curious man...so you'll just have to forgive me my impatience, OK?

Can you tell us what you found, and how it made sense? I am interested in what you have to say and if we wait too long...you might be telling me I forgot, I have these ideas all wrong, and my thinking is apples and oranges again.



I can honestly say I've never heard anybody make such a claim, saying the Imax had a capacitor in its middle section until a while back.

357 what more do you know about this story?

All I can recall is thinking the object noted in the middle section was a noise damper, I personally checked it out on at least two occasions back in the days. Maybe I even posted something about those incidents, back then. I will do a search of my notes and on the forum.

DB did you ever talk about it when you found out the Imax had a capacitor as part of the antenna?



When I recently asked you what the value was, I made a note that you told me it was 25pf. I too chased my tail for a while like you tell us you did. I posted the other day that when I used 25 and a variety of other values...I could tell that something was happening and that the cap had an effect. I can only guess what effect the cap has, however. So I repeat...what is your opinion why Solarcon does this?



Based on the information that I posted for NB about the guy in my area posting an article on the Internet about his using 1/2 wave and longer radials slanted down on his Imax...I too am curious to know your opinions on this too...when you get time.

It is this part of this project in the link below, a possible collinear effect, that intrigues me.

click here: IMAX 2000 continuity query​

Like I think I've said already...I saw something similar to a collinear effect in the second Nec2 model you posted for this idea for a capacitor in the middle of section 2 on the Imax.

How say you?

Hey Eddie, not the best time for me right now due to the stress of house shopping, bidding, countering, inspections, sleeping in noisy hotels, etc., but..

It appears the capacitor not only helps to isolate the upper half of the antenna from undesirable high voltage contact but realigns the phase to compare favorably with the Gain Master in current distribution.

With appropriate counterpoise or decoupling (or BOTH) I expect it might continue to outperform metal 5/8 antennas as I've seen it do mine.

 

[The DB]

Eddie, I know you asked me lots of questions, but I am not anywhere near a computer at the moment and cannot sit down and answer them properly.


The DB

 

[Marconi]

Hey Eddie, not the best time for me right now due to the stress of house shopping, bidding, countering, inspections, sleeping in noisy hotels, etc., but..

NB, it was late when you posted the nice scenic pictures of the sun shining through the trees, but I got the idea you already picked out a new place with 100's of very tall trees just waiting for antennas to be installed. Or, were you just giving us a mental image of your dreams

It appears the capacitor not only helps to isolate the upper half of the antenna from undesirable high voltage contact but realigns the phase to compare favorably with the Gain Master in current distribution.

NB, you'll have to explain this a bit more simple for me to understand what you mean here.

I can't be sure, but I think maybe DB has found the capacitor does add gain too, but at this point, my model does not show more gain. The way I read my results my model shows >50% reduction in current on the radiator compared to my model of a regular Imax width or without radials and no capacitor.

NB, I don't know why this happens with my model, but I would guess that DB probably disagrees with me that the Imax with the capacitor shows no benefit for performance unless the idea is to minimize CMC. NB, maybe I missed the news being well established that this capacitor idea really fixes the Imax...making it the hottest CB vertical antenna around.

With appropriate counterpoise or decoupling (or BOTH) I expect it might continue to outperform metal 5/8 antennas as I've seen it do mine.

Get your hip boots on fellas, it is getting deep around here. Whatever happened to your .63..64 wave Super Penetrator ideas?

Nevermind me guys...I'm just venting a bit, I want to get this Imax idea behind me.
I for one have not given up on the SP500 being among the best CB vertical antennas available, and that is according to my current model of the antenna without any matching. In my Eznec model, however, I have carefully modeled the mounting bracket that looks to effectively raise the radials up about 12" inches on the radiator. I have not posted much about this possible sleeper.

1. because I'm not yet fully confident the model is accurate.
2. you guys probably won't believe it anyway.

 

[Marconi]

Eddie, I know you asked me lots of questions, but I am not anywhere near a computer at the moment and cannot sit down and answer them properly.

The DB

Thanks, that is a relief DB...I thought maybe you were upset with me for putting my two cents into this capacitor idea.

Then I'll go back and re-read your earlier post. That stuff might make more sense now, and maybe it will answer some of my questions while you get time.

 

[Marconi]

Now I'm off to listen to my music, enjoy if you will.

 

[bob85]

The DB told us adding the cap raises end impedance closer to that of a 1/2wave.
Common sense tells us current in the end segments would drop.
Look for peak current along the radiator.
If thats 50% low its time to call Houston.

 

[Marconi]

The DB told us adding the cap raises end impedance closer to that of a 1/2wave.
Common sense tells us current in the end segments would drop.
Look for peak current along the radiator.

If thats 50% low its time to call Houston.

I can't be sure, but I think maybe DB has found the capacitor does add gain, but at this point, my model does not show more gain. The way I read my results my model shows >50% reduction in current on the radiator compared to my model of a regular Imax width or without radials and no capacitor.

Bob, you're right. I did make this comment about currents on the radiator being 50% lower on the model with the capacitor, as noted in my post above. I was surprised that my model showed me that low of currents. It really didn't make sense, like you said.

When I read your post I went back and checked the two models for any differences. There was a setting in the model with the capacitor added where I had the power set to default watts, about 52 watts. The model with no capacitor had the power set at 100 watts...so I fixed the model to make these setting the same. I added this info to the exhibits I posted below. I noted the currents for wires #1 and segment #2 and for the maximum current at the center of the radiator which was segment 41 or 42 on the model.

Thanks

As soon as DB and I get together again...we will probably find other little differences between our models...but I think we are close. Now I see the similarity in the patterns with my models that have the capacitor...very much like DB reported earlier.

In the PDF file below I have an overlay of all these models in two groups.
1. Imax with the capacitor
2. Imax without the capacitor

Sorry for the bad notes.

In the PDF below I added the antenna view to the overlays in order for us to see the actual currents. Here we see the currents on the mast for both models, but the model with the capacitor is out-of-phase with the radiator, and it is the opposite situation with the model without the capacitor.

I have not studied all of these models comparing the currents on the mast that we see in the Antenna View, but I would expect the models with a capacitor to show the primary mast currents out-of-phase with the radiator. It is just my opinion this condition difference might be what hurts the gain in the real world sometimes as well.

As further support of this idea that the mast currents might be helpful or not, I also predict that I will see reduced gain in the models that are (ISO) isolated. This is, at least, evident in the two overlays for these two groups I posted.

At this point, I tend to believe the match makes little to no difference in the performance results for a model, so I'm considering mast currents can be beneficial at times and I guess the big question is...how do we know when this condition happens?

Thanks for the help.

 

[Needle Bender]

Marconi, thank you for sharing that music, it's excellent(!) and I can't wait
to hear it on my Home speakers & amp once they're set up in the new theatre room.

OK now, on your model, why not try a 41' high base (current max @ 1.5 WL AGL) and 9' downward sloping (65°) radials in full-ISO - against the best from your last model.

And as far as my undying allegiance to the .64, I've never been die-hard-nosed about any specific design, only the one which works best for the / my application.

If I find the Imax+radials has in fact "repeatably' superior performance in comparison to a metal 5/8 - .64, then I'll probably still have metal in the tree, but it'll be modded & hopefully perform at least as well as the Imax, unless I wrap an Imax with 10lbs of fiberglass and basically make a Phelps - Dodge Stationmaster out of it!

I'm hoping only one trip to the ~160' tree top will suffice for at least a decade.

 

[357]