Difference in AstroPlane vs. New Top One per Eznec5

[Marconi]

NB, it looks like your idea could have some merit. Here is a 3/4 wave with radials slanted up beside the 1st 1/4 wave of the antenna a little bit. The FS pattern looks very similar to the other four models for a 1/2 wave, but it is skewed just a little bit. I wouldn't argue the difference though. I have no problem with your idea. Is that something that you have pondered or did you get it from another source?

I also added a mast and did the model using Eznec's real Earth feature.

View attachment NB's idea for .75 wave.pdf

 

[gamegetter]

I made a note in my manual and it shows the top of the first coax coil to the tip is 22'4".

What do you mean, "Or is that length the actual length of the wire inside the coax?"

BTW, since I found some errors in my A/P model, I checked my New Top One model and I found several dimension errors there too. I also had my hoop too big, and the number of segment sides was wrong (and odd number) and did not space out the four legs equally on the circumference.

I have more work to do on the NTO, but I think I'll send the A/P model off to Roy Lewallen and see if he will kindly give me a critique and maybe some pointers.

Marconi:

Disregard my length question...I found this on sirio's gainmaster and I believe now that your model length is good enough, the pic shows an effective length of 6.9 meters which is about 22.6 feet after I convert. Attached pic for everyone's viewing. I still will have some question in my mind about it's actual length, but someday i will get one and measure it. Either way Sirio was attempting to improve on the 5/8 wave and I shall leave it at that.

Needlebender:

I wait to see where you came up with your 3/4 wL theory for the AP. There is no mention on the AP patent and I don't see why they would label their original box as a 5/8 wave and risk false advertisement claim.

But i do see from the modeling how they possibly were attempting to improve the 1/2 wL and how through the use of historical naming they could call it a 5/8 wL.

Some very interesting discussion here thanks for all contributing.
P.S. forgot to post picture on gainmaster for Marconi,,,please hold.

 

[Marconi]

Marconi:

Disregard my length question...I found this on sirio's gainmaster and I believe now that your model length is good enough, the pic shows an effective length of 6.9 meters which is about 22.6 feet after I convert. Attached pic for everyone's viewing. I still will have some question in my mind about it's actual length, but someday i will get one and measure it. Either way Sirio was attempting to improve on the 5/8 wave and I shall leave it at that.

Needlebender:

I wait to see where you came up with your 3/4 wL theory for the AP. There is no mention on the AP patent and I don't see why they would label their original box as a 5/8 wave and risk false advertisement claim.

But i do see from the modeling how they possibly were attempting to improve the 1/2 wL and how through the use of historical naming they could call it a 5/8 wL.

Some very interesting discussion here thanks for all contributing.
P.S. forgot to post picture on gainmaster for Marconi,,,please hold.

Gamegetter, do you see how the bottom portion of this antenna, with the stub attached, actually radiates using the pesky common mode currents effectively, and how the choke must really be doing its work to stop those currents from flowing on down the feed line?

 

[gamegetter]

theoretically i know they are 1. matching load and antenna and 2. the choke preventing the flow of current back, thereby maximizing power...but i am not an electrical engineer or well versed in electricity per se.

 

[Needle Bender]

NB, it looks like your idea could have some merit. Here is a 3/4 wave with radials slanted up beside the 1st 1/4 wave of the antenna a little bit. The FS pattern looks very similar to the other four models for a 1/2 wave, but it is skewed just a little bit. I wouldn't argue the difference though. I have no problem with your idea. Is that something that you have pondered or did you get it from another source?

I also added a mast and did the model using Eznec's real Earth feature.

View attachment 7156

That appears to mimic a Vector. I was only surmising the AP shape appeared as a folded 3/4 wave so that the bottom 1/4 wave is physically inverse to the top 1/2 wave causing it to rephase back to being in-phase with the center 1/4 wave of the 3/4 total.

Pi was for determining the length of 1/2 the circumference of the ring:
30" x pi = 92.25"

92.25"/2 = 47.125"

1/2 the 1/2" ring tubing circumference = .79"

47.125" + .79" = ~48" to complete the bottom 1/2 wave made by the two 7' down tubes + 1/2 the ring = 18'.

Gamegetter, I believe the overall physical length, including the length of the cap hat, is about 5/8 wave, though with a capacitance hat it acts longer when completing the top 1/4 wave, making the antenna an electrical 3/4 wave (which radiates as a 1/2 wave) is my best guess.
I don't see how it could be otherwise since it is direct-fed and measures so close to an electrical 3/4 wave with the cap hat, plus would have to have a max current/min voltage node where it touches ground at the mounting plate and base of the top 1/4 wave, or else it would have ~zero RF impedance.

 

[HomerBB]

Ok Marconi, here are the results of the scans as promised.

First scan , antenna 16' elevation:

I tightened everything up because I notice fluctuations on the meter:

Best reading

So I decided to see what moving the center strap down 1" would do:

Moved center strap additional inch:

I moved the strap down an additional 1" and the tune began to falter. There seems to be a limit to how much adjustment can be expected of the strap movement. Then I tried moving the whole thing up in the top bracket 1.5" assuming the readings might respond to a shortening of the antenna from the fed side. Nope. The whole tune went away. I did not get photos of that.

The width of the connection points on the middle separator, or strap as I call it, is 12".

Not knowing whether the PVC construction lacks the necessary rigidity to maintain proper uniformity when the antenna is mechanically manipulated, the only thing I can do from here is rebuild the antenna from metal that will hold its form more rigidly and see what that accomplishes.

 

[Needle Bender]

Homer, if it is a folded 3/4 wave as I believe it to be, then that strap is centered at the 0 voltage & max current node, so moving it much up or down will cause it to begin shorting voltage to ground, if you're working with upper 1/4 wave side of the mounting plate of the AP and I haven't missed something :blushing:

 

[Marconi]

Ok Marconi, here are the results of the scans as promised.

First scan , antenna 16' elevation:

I tightened everything up because I notice fluctuations on the meter:

Best reading

So I decided to see what moving the center strap down 1" would do:

Moved center strap additional inch:

I moved the strap down an additional 1" and the tune began to falter. There seems to be a limit to how much adjustment can be expected of the strap movement. Then I tried moving the whole thing up in the top bracket 1.5" assuming the readings might respond to a shortening of the antenna from the fed side. Nope. The whole tune went away. I did not get photos of that.

The width of the connection points on the middle separator, or strap as I call it, is 12".

Not knowing whether the PVC construction lacks the necessary rigidity to maintain proper uniformity when the antenna is mechanically manipulated, the only thing I can do from here is rebuild the antenna from metal that will hold its form more rigidly and see what that accomplishes.

Here is my A/P model that I recently adjusted for best dimensions. It has the source set on top of wire #4. I also included the pattern view.

My strap shows to be 5.5" on each side at the center of each wire, but when I checked it on the new take-off sheet I did the other day, I noted I didn't change it on the model. It should be 12.5" as per my Top One. I'll have to fix that, and then I'll play with moving it to see if it changes frequency.

I'll also make the adjustments to the strap changes you did 1" at a time and see if that changes the match as you noted. I assume you left the strap bracket between the radials the same length and just moved it up and down on the radials...except for the last adjustement, right? If so, then it is good to know that the last change to the radial length, an adjustment that changes more that just the bow in the down radials, is a no-way-no move.

View attachment AstroPlane Default at 26.525 mhz..pdf

The similarity of these two results are remarkable. Thanks so much for helping me.

 

[HomerBB]

I'll also make the adjustments to the strap changes you did 1" at a time and see if that changes the match as you noted. I assume you left the strap bracket between the radials the same length and just moved it up and down on the radials...except for the last adjustment, right? If so, then it is good to know that the last change to the radial length, an adjustment that changes more that just the bow in the down radials, is a no-way-no move.

View attachment 7161

Your assumption for leaving the spacing between the same is correct.
And, yes, I wouldn't be screwing with the placement on the top bracket at all!

The similarity of these two results are remarkable. Thanks so much for helping me.

Yep

 

[HomerBB]

Homer, if it is a folded 3/4 wave as I believe it to be, then that strap is centered at the 0 voltage & max current node, so moving it much up or down will cause it to begin shorting voltage to ground, if you're working with upper 1/4 wave side of the mounting plate of the AP and I haven't missed something :blushing:

The speculation on what exactly the AP is continues. Certainly its electrical properties define it more so than the physical properties do. It is off-sized for 11 meters . . .

I did move the entire vertical section on all sides upward in the top mounting bracket as a last modification to check what the results might be. . . not good.

Now that I have replaced everything to the starting point, I find I did not recover original readings. I think that is a issue relative to the nature of the flexible tubing I've used. I must redo the antenna with aluminum to be sure, it seems.

 

[Marconi]

Your assumption for leaving the spacing between the same is correct.
And, yes, I wouldn't be screwing with the placement on the top bracket at all!


Yep

Well Homer, I fixed my strap to 12.5" and the frequency went down from 26.525 to 26.495 the wrong way. Now I'll have to retry moving the strap on the radials, like you did.

To confirm I rechecked the mm sheet and there I figured that the strap item 6 was 12.625", but my Top One strap I call a bracket is 12.5" center to center on the radial bolts where it's attached.

That mm sheet looks pretty accurate, but the top hat elements are shorter by an inch than my Top One, and it also shows the hoop is 29.5" and my model is set at 30", so I'll have to see what changing that does also. If it makes the antenna shorter going to 29.5", and if it makes it considerably shorter electrically...it might raise the frequency. Shortening the top hat should show a similar result.

 

[Needle Bender]

The speculation on what exactly the AP is continues. Certainly its electrical properties define it more so than the physical properties do. It is off-sized for 11 meters . . .

Marconi, do you recall how long you had to make the top section of the AP (from the bracket - up) when you removed the top hat radials and replaced them with straight tubing?

It would be interesting to model a simple Starduster & a 1/4 wave GP, but with an identical shortened top, & top hat (as per the stock AP) instead of a straight 1/4 wave, just to see where they would resonate.

I can't imagine an antenna other than a 1/4 wave or 3/4 wave which can be driven directly without a matching network and still have a 50 ohm load with near zero reactance.

Maybe I should get up on the roof and stand up my old Avanti AP and start measuring... :bored:

 

[Marconi]

Homer, I lowered the strap 1" and the reactive part of the match did go down a little, and improved the match just like your antenna did. The resistive part also when up a bit, just like your antenna did.

I didn't see a notable difference in the frequency like you did, but the antenna got shorter going more (-) capacitive, and in my case with my model being a little inductive to start...the frequency did go up some no doubt.

That is remarkable.

Since you bottomed out at 1' lower, I didn't go down another inch.

I then went up 2" inches and the match went more inductive (+) and that is longer and thus the frequency dropped, so I now know the frequency for the match can be adjusted using this model and this adjustment is just as Avanti said in the patent. The model works just like your real antenna. I wouldn't expect our results to be anything but similar, but to show this much similarity with small changes is truly remarkable.

Going down with the strap makes the frequency go up (antenna shorter), and going up with the strap makes the frequency go down (antenna longer).

So, sports fans and critics of modeling, what does this suggest about my A/P model?

 

[Needle Bender]

So, sports fans and critiques of modeling, what does this suggest about my A/P model?

Did you mean a New Top One model?

I just went back to pg1 and realized that I missed reading posts 11 - 40!

 

[HomerBB]

Marconi, fix this in your post:

Going down with the strap makes the frequency go up (antenna shorter), and going down with the strap makes the frequency go down (antenna longer).

It should read UP

I know that's what you meant.