Difference in AstroPlane vs. New Top One per Eznec5

[bob85]

to change the impedance of a transmission line significantly you change the spacing, small hub small hoop = lower impedance higher resonant frequency, its explained in the arrl open sleeve article,

your models show that altering the bow changed impedance as expected of a transmission line, less bow higher impedance,

to discover if nec reports that avanti were bsing us over the means to create downtilt in that style antenna i think you may need to find the right size hoop and hub that gives a good match to 50ohm coax when the conductors are parallel to a 1/2wave mast,

since avanti claim a takeoff angle of about 4-5 degrees with the stock setup vs your 9 degrees you may not see the downtilt they claim using parallel conductors.

 

[Marconi]

to change the impedance of a transmission line significantly you change the spacing, small hub small hoop = lower impedance higher resonant frequency, its explained in the arrl open sleeve article,

your models show that altering the bow changed impedance as expected of a transmission line, less bow higher impedance,

to discover if nec reports that avanti were bsing us over the means to create downtilt in that style antenna i think you may need to find the right size hoop and hub that gives a good match to 50ohm coax when the conductors are parallel to a 1/2wave mast,

since avanti claim a takeoff angle of about 4-5 degrees with the stock setup vs your 9 degrees you may not see the downtilt they claim using parallel conductors.

Thank you Bob, I'm re-working my understanding here, and so far I find you're right again. I was making a stupid mistake considering these models after each adjustment in the radial bow, but before I checked the match I re-tuned the antenna to the best frequency. The match, more or less, always returned to the start, so I wasn't seeing the match change...just the little change in frequency. Now I see that what you're saying should be going with my model is true.

Thus I believe all this worry about trying to re-tune the A/P is a fruitless effort if you're working CB with it. The bandwidth is wide enough to not require in tuning except for maybe the die hard antenna nut or if you wanted to build one for another band like Homer might would do.

Everything below is subject to change, but this is the way I see such adjustments going for now. The bow does effect the impedance and frequency, and going down looks to be the way to go...to make the impedance drop. My models show the stock A/P antenna tending to be a little inductive at 45' feet, with the value of resistance a little high at R=60<>, and I tend to see this in my real world bandwidth curves too.

A note to Homer. Bob doesn't say which way your strap should go, but I find the frequency goes up on lowering the strap and I see that as making more of a bow in the radials and that does agree with what he says. Now that I'm seeing this, maybe you could check your antenna again as you lower the strap. I that case with these models I see the value of R go lower to virtually R=50 ohms at resonance. I dropped the strap a total of 18" in the process, and I didn't see any instability in the match as you did earlier. If you get a chance to recheck your A/P let me know, OK?

Bob, my next step is to check for detectable signs of a downtilt, as you suggest. This has to do with your other idea, and your comment above about a 1/2 wave mast.

I'm not sure of the importance of the following, but I noticed one thing in checking the mast currents on the current log. First off the currents remain in the same pattern of phase as the original model which I described earlier in this thread as being good. The segment length for my mast is set at 1' foot. There are 21 segments in the top of the mast attached to the hub that are in-phase with the top of the antenna and radiating, both above and below the hoop.

I know the patent says this mast should extend below the hoop at least a distance equal to the length of the down radials, and that also suggest the mast should be at least a 1/2 wave length. However, the typical mast would be about 4-5 times larger in diameter than the radials, and for me that would tend to make it physically longer than it should be, so I'm not too sure about my 21' foot mast idea sitting on the ground at a voltage node. Do you have a physical height in mind that Avanti may have used?

As far as the angle you mention. I think the pattern image that Avanti uses in their Patent is a free space model, and I haven't produced that as yet. These models are over average soil and Eznec5 idea of real Earth. Typically I remove the mast in free space models for my other models, but I believe I proved to you the other day that the A/P is worthless without a conductive mast, so if I do a FS model I will retain the mast sticking out below the antenna. In that case I will also add length to the model and see if it makes a difference and of course I will make it shorter to test the downtilt idea.

 

[bob85]

i think a mast 1-1/2" diameter extending 8-9ft below the hoop not grounded is what avanti meant, since the measurements were taken on vhf chances are the antenna was well above ground relative to frequency,

remember what is a high impedance low current not grounded becomes a low impedance high current when grounded,
the worst case length depends on the mast been gounded or not.

 

[Marconi]

to change the impedance of a transmission line significantly you change the spacing, small hub small hoop = lower impedance higher resonant frequency, its explained in the arrl open sleeve article,

your models show that altering the bow changed impedance as expected of a transmission line, less bow higher impedance,

to discover if nec reports that avanti were bsing us over the means to create downtilt in that style antenna i think you may need to find the right size hoop and hub that gives a good match to 50ohm coax when the conductors are parallel to a 1/2wave mast,

since avanti claim a takeoff angle of about 4-5 degrees with the stock setup vs your 9 degrees you may not see the downtilt they claim using parallel conductors.

The Patent says the 146 mhz mast was 33.5" and that's about right for a 1/2 wave, but they don't tell the height for their real world test. But I'm pretty sure they were calculating for free space, plus the pattern in the Patent looks like a free space model. So, below is a series of free space models at different heights. It is remarkable how height affects this A/P antenna or maybe I should say doesn't affect it. Before now I don't think I've every done one of these in free space, and the very low angle results surprised me.

I made some notes and added high lites in some areas of interest. You also mentioned that Avanti probably did their model above ground. Well I did these models attached to the ground with the specific length of the mast noted to the left under wire #45, but the Earth connection affect the patterns and results very little. When I did the models I forgot to make the disconnect to the Earth, but I did check a few out, and noted hardly any differences.

With free space models the ground is not consider in the scan. That is the whole point for using free space models to eliminate and and all losses that we are concerned with when the Earth and other stuff affects our antennas. Another reason to know that Avanti did their model work in free space. Now we see the 4* - 5* and less patterns mentioned. I knew that I had see patterns that indicated maximum angles below the horizon, but I didn't recall them being the A/P. I don't do much with free space models.

Ordinarily I would remove the mast when doing a free space model, but in this case the A/P needs the mast to work.

Also take close notice of the models at 4' and 5' feet. The 4' foot height is also noted with a warning in the A/P manual, so check how this small range from 4' - 5' affects the match. Maybe this is what Avanti was referring to when they made the warning with regard to a minimum 4' clearance for stuff below the antenna including guy wires. These models may also suggest why folks have repeatedly told us the A/P works very well down low, but when I tested over Eznec5 real world feature the other day, we note that the Earth affects have a different story to tell. Maybe this also suggest to us how stories can get started in a lack of understanding.

Virtually all of this surprises me.

View attachment AstroPlane height to ground .pdf

 

[bob85]

well you found downtilt eddie, i have not seen other common cb antennas do that with different length masts,
does the mast have so much effect when its not connected to ground?

what does that say about your tests at different heights with the astroplane?

 

[Marconi]

well you found downtilt eddie, i have not seen other common cb antennas do that with different length masts,
does the mast have so much effect when its not connected to ground?

what does that say about your tests at different heights with the astroplane?

Bob, I really haven't studied these models enough to make a determination on what I think except to say again, variations in height does not affect free space models much if any.

IMO, the connection to Earth doesn't much matter either when in free space. I'll post several of these models for comparison over real Earth...after I have a chance to throughly look them over, and maybe even pick out some specific examples, like 4', 5', 18', and 36'. This is a learning experience for me, I'm just winging it as I go...uncharted waters, so-to-speak.

My main goal in my modeling is to make the models for these CB antennas as accurate to dimensions as possible. So far, correcting these dimensions seems proof to me...that is the right way to go to make a better model.

When I set these same models up using Eznec5's real world Earth feature, you will start to see that height matters, and when the Earth gets involved with your antenna, that's the way it is, Earth matters...I think.

I also don't think we'll see any patterns close to looking like a tilt with the real Earth models or the very low angles to be noted. Free space models are intended to take out all losses possible and just test the radiator and whatever is attached to it.

I think this project also might help explain how and why the mast is so important to the A/P design, but that the length of the mast is less important at the same time...as long as the mast is long enough, (4' at least). I'm not sure that there is a best case scenario to be noted here, however.

Regarding your last question, this tells me that the models over real Earth matter too, and we won't be seeing the same lack of affects, cause old Mother Earth rules...and will have her way.

Now, I'm off to try and make the New Top One model better, or get back to working on Cebik's ideas for a better model on my I-10K and see how much difference all this worry about models makes.


I think I've may have already noted that the I-10K does not seem to work too well when close to the Earth using my model as an example.That model is strange too, it shows some unexpected horizontal RF that I only see with my Wolf .64, but I'm still pretty sure the I-10K needs some height with it's big old ground plane radials sticking out. I may find the .64 does the same. I may not be right, but I say what else can I do to find out, check out the words of wisdom written on the walls of my local Truck Stop?

73's

 

[Marconi]

Here are several of the previous free space models I converted to Eznec's real Earth feature. I made notes and added an over lay of some other models. Bob, this sort of supports your idea for not liking free space models since there is so much difference. This may be unique to the A/P design, but I'm not sure of that.

The rank I see in the overlay is:

Blue best gain
Purple
Lime lowest angle
Turquoise

View attachment AstroPlane over real Earth.pdf

 

[Marconi]

Marconi, what would this forum be without your colorfulness! Never stop keeping things rolling!

Regarding the I10k, I agree with Bob85 in that the I10k is an incredibly well built, strong-as-an-ox bottom-fed 5/8 which performs a whole lot like a bottom-fed 5/8, exactly like a SigmaII 5/8 and every other bottom-fed 5/8 out there.

There is no voodoo, magic or ultra-efficient anything which makes even a needle width improvement over any other 22.5' 5/8, but if I lived on top of a very windy hilltop- I'd have to have one.

If you read around you will find people claiming 2-3 s units improvement when compared to a Penetrator. That's just BS soaking in snake oil.

Regarding raising the resonant frequency of the AP, don't you think you should also shorten the base proportionally to the top so you keep the mounting plate at the point of highest current?

Thanks for the kind words NB, I think.

Do me a favor if you can. If you have your I-10K up and working, check around with a buddy that has a horizontal beam that shows good polarity isolation.

Check the results on the images below, showing my I-10K model with a strong horizontal portion on the pattern display. The horizontal is dominating the power by a a significant amount. Then do a signal check with your guy. I'm interested to see if you can note a horizontal response with your vertical. If he and you happened to each have another vertical up and working, then that could be another comparison check you could do, and let me know, OK?

I didn't do anything special to this model except add the trombone tuner to it and try and make sure the dimensions and angles are all as close as I could get, and I don't understand this response.

View attachment I-10K polarity check.pdf

 

[Needle Bender]

Thanks for the kind words NB, I think.

Do me a favor if you can. If you have your I-10K up and working, check around with a buddy that has a horizontal beam that shows good polarity isolation.

Check the results on the images below, showing my I-10K model with a strong horizontal portion on the pattern display. The horizontal is dominating the power by a a significant amount. Then do a signal check with your guy. I'm interested to see if you can note a horizontal response with your vertical. If he and you happened to each have another vertical up and working, then that could be another comparison check you could do, and let me know, OK?

I didn't do anything special to this model except add the trombone tuner to it and try and make sure the dimensions and angles are all as close as I could get, and I don't understand this response.

View attachment 7228

Hi Marconi,
To answer your question, I would bet you're seeing horizontal ground-gain factored in, providing such a high level on the graph.

I never noticed superior horizontal to vertical performance using my I10k before I sold it, but I did notice a lot less horizontal information when I switched to a radial-less Imax.
Guys that went horizontal all but disappeared on the Imax where I could normally still hear them fairly well when using the I10k or Penetrator, but nowhere near as well as when they were vertical, even when pointed right at me during both polarization tests.

Possibly there would be less horizontal interaction/cancellation/directional dilution if there was only one radial instead of four, and if the antenna was both mounted isolated from any metallic mast and the coax was sufficiently choked?

 

[Marconi]

Hi Marconi,
To answer your question, I would bet you're seeing horizontal ground-gain factored in, providing such a high level on the graph.

I never noticed superior horizontal to vertical performance using my I10k before I sold it, but I did notice a lot less horizontal information when I switched to a radial-less Imax.
Guys that went horizontal all but disappeared on the Imax where I could normally still hear them fairly well when using the I10k or Penetrator, but nowhere near as well as when they were vertical, even when pointed right at me during both polarization tests.

Possibly there would be less horizontal interaction/cancellation/directional dilution if there was only one radial instead of four, and if the antenna was both mounted isolated from any metallic mast and the coax was sufficiently choked?

What you say may all be true, but I only saw the horizontal patterns start to emerge after I added the trombone tuner to a generic 5/8 wave ground plane I had, and it did not indicate any horizontal pattern at all prior to that point.

Since I made the patterns I posted in my request to you, I have fixed several dimension errors in the matcher that I found in my original model, and with each correction the model continued to get better and better...concerning the things I can control on a real antenna, the match and resonance. As a result the horizontal pattern became less dominate than the vertical pattern, and I realized not only does getting the right dimensions and angles make a notable difference, but the matcher added to the model tends to start generating this vertical/horizontal combination that I don't see with most other antennas I've modeled.

Your comment above gives me all that I needed, thanks. You saw a better responses from a locals with horizontal beam on your I-10K, better responses than your Imax showed. That is what I once saw too, when real world testing one of my AstroPlane antennas. I was able to duplicate that test too with other local operators, but I never saw it on any other antenna, including my I-10K that I was aware of, and I could not detect same with DX signals either.

Thanks for your help NB, you gave me just what I would expect from someone that was watching their business closely, and I'm convinced this horizontal thing with the I-10K makes it somewhat unique, in spite of your insistence that a 5/8, is a 5/8, is a 5/8.

But that is OK, I believed that until I was shown some evidence to the contrary, and I think this model proves that. I also think the RF field test that Tech 833, from Copper's Website also reported that something strange was going on with the I-10K he test for Jay. Tech 833, however claimed the issue would likely produce RFI problems, and according to Tech 833, Jay refused him the rights to publish the report. If I can find the link, I'll post it.

Thanks again,

73's

Here is the link: Copper Talk sorry the link will not work unless you have access to the Members area. I'll try something else.

 

[Marconi]

Copper's Tech 833 review of Jay's I-10K

NB, here is a PDF file of the report that Tech 833, over on the Copper's Forum did for Jay's I-10K.

View attachment Copper's Tech 833 review I-10K.pdf

 

[bob85]

the models with short masts connected to ground are interesting but not as the antenna would typically be used so low to the ground,
its hard to determine what effect been so near the ground has and what effect the length of the mast plays,

the 36ft+ models are typical and it would be nice to see if isolating the mast on those models different distances below the mast effected the pattern

 

[Marconi]

the models with short masts connected to ground are interesting but not as the antenna would typically be used so low to the ground,
its hard to determine what effect been so near the ground has and what effect the length of the mast plays,

the 36ft+ models are typical and it would be nice to see if isolating the mast on those models different distances below the mast effected the pattern

I've finished on my I-10K project for a while, I still have to figure out how to control and get the value of R up a little bit, but that will be another day.

I'll check out your idea if I understand you right. Are you thinking of isolating near a point on the mast about 1/2 wave. I think that is what Homer was attempting to do using a choke somewhere well below the hoop, but I'm not sure. I don't think he is working on his A/P yet. He might have done something after removing the choke, and maybe he saw some difference, or maybe not. If that is the way it went, then he was probably trying some version of an idea that I think I've heard you talk about too. I'll do this model over real Earth and you won't likely be seeing the tilt thing or the lower angles, but I could be wrong again.

To make sure, tell me what dimensions you would like for me to fix the model, and I will set the base at 36' or the hub at 36', which ever you want. Or, I'll even diddle it around a bit and see if I can find a sweet spot.

Working with the mast only takes a few key strokes once I figure out the measurements. Let me know if you're thinking about isolating at the bottom of a 1/2 wave mast or not, and then we'll have to try and figure out what that 1/2 wave length is for the the 1" mast I used. I think I asked you earlier what that length might be, since the mast is much larger than the radials, but I don't recall your answer and I looked back a little and didn't see a response, so I ask again.

 

[bob85]

if you can set the hub at say 36ft above earth and vary the mast lengh below the hub starting with 1/2wave mast or 8-9ft below the hoop, then shorten the mast to less than 4ft below the hoop to test the rising takeoff claim and maybe extend it longer to 3/4wave or 17-18' below hoop,

i think they were bending the truth when they claimed in the patent that other antennas had max current and radiation in the base of the antenna.

 

[Marconi]

if you can set the hub at say 36ft above earth and vary the mast lengh below the hub starting with 1/2wave mast or 8-9ft below the hoop, then shorten the mast to less than 4ft below the hoop to test the rising takeoff claim and maybe extend it longer to 3/4wave or 17-18' below hoop,

i think they were bending the truth when they claimed in the patent that other antennas had max current and radiation in the base of the antenna.

I didn't do exactly as you wanted, but this close. I made notes, so I hope I made them clearly. BTW, I just added 8.5' to the part inside the radials to get 15.855' feet. I think there is 7.355' of mast inside the radials for this model.

View attachment Bob's idea on mast length and isolation ISO.pdf