Difference in AstroPlane vs. New Top One per Eznec5

[gamegetter]

both would be interesting for the direct radiation pattern and image reflected by the ground, but i don't want to trouble you if it is alot, just don't like to leave any stones unturned by guessing what the pattern and reflection might do.

it would be interesting to see what they were seeing back then when they modeled it in the early 70's as they expected a low ground install versus what one would see today if installed as high as possible.

good day.

 

[Marconi]

both would be interesting for the direct radiation pattern and image reflected by the ground, but i don't want to trouble you if it is alot, just don't like to leave any stones unturned by guessing what the pattern and reflection might do.

it would be interesting to see what they were seeing back then when they modeled it in the early 70's as they expected a low ground install versus what one would see today if installed as high as possible.

good day.

Changing height is not problem. Just a few key strokes and you're done.

Based on the 20' foot limit noted here, that would allow an AstroPlane to be mounted at 16' feet to the hub mounted on the ground, not 12' feet. When mounted on the ground an EF 1/2 wave would be at 2' feet above the ground and follow the rule.

View attachment AstroPlane vs. EF .50 wave at 20' feet to tips.pdf

 

[Marconi]

greetings guys;

i playing catch up as i could not get back on last night...

it appears to me that "physically" the AP top is a 1/8 wave, but electrically it is a 1/4 wave with the top hat and the hat does not need to measure out physically to exhibit the 1/4 wave, i'm sure you are aware of that. And so you just have to explain it as such.

Now with the 12' mast info you provided BM and thanks, which i had not had time to look up the distance exactly (which is why i referenced the 20' max height restriction of when it was designed for)...12'+9'(electrical)=21' very close to the 5/8 wave they describe on the original box and it would fit nicely for those folks observing the max legal limit at the time!

How do you get your 9' foot dimension?

 

[gamegetter]

it is electrically a 1/4 wave up on top, even though physically the radiator is a vertical 1/8 + what ever the top hat is...

this is where I would say they used a play on their words to get the 5/8th and advertise it on the box-as you called it "eye candy"

do you follow? the top hat will not give the radiator the actual physical dimension but electrically it does "act" like the 1/4 wave, there fore they "used" the physical dimension of a 1/4 wave-approximately 9 feet.

 

[gamegetter]

very nice

with the smaller/compact astroplane they were able to show a gain of 1.68 db over the 1/2wave and lower the direct radiation pattern 1degree...all theoretically of course. everyones mileage would vary in the real world.

this is giving me some good insight on the antenna history. thank you sir.

 

[massacre77]

whare can i buy this antenna?

 

[Marconi]

whare can i buy this antenna?

77, you will have to locate one used, the original AstroPlane is not made anymore. Sirio makes a new model called the New Top One. It's a bit different, but I find it works just as good or even a little better. It has a wider bandwidth too.

I also found it required no tuning when I put it together just as the instructions suggest. My bandwidth shows below 1.5:1 SWR from 26.305 - 28.500 mhz and over 5 mhz below 2.00:1.

Not many use these antenna, but they work remarkably well considering they are only 12' feet tall and light.

 

[Marconi]

If I read it right it appears the NTO had a 0.09dbi over the AP in the lowest lobe, however, It seemed the secondary major lobes were superior in the AP to those of the NTO in terms of lower DX angles.
Did I see that correctly?

You did see it correctly Homer. Additionally the NTO's increase in gain may be attributed to its increased height, and the fact that its model shows more current flowing on the mast below which can unpredictably add to gain, but usually at higher angles.

Model #4 below is the same as the previous A/P model. I took this model and fixed it to improve the excessive currents on the mast that the hoop did not decouple, and then made it my model #5.

By improving these currents termination at the hoop, for the bottom 1/4 wave portion of the mast inside the two down radials, we can see improvement in the model. The antenna now produces a pattern that is more like the traditional EF 1/2 wave. Its current pattern also shows a better balance of currents across the 12' foot length for the radiator. This model also produces a wider pattern wave front near the horizon with higher gain in the secondary lobe and with very little low angle null area.

View attachment Models 4 - 5.pdf

 

[HomerBB]

I know you are working with modeling software, but by what mechanical change would you fix the excessive mast currents on a real antenna. It must have a mechanical equivalent to have practicality, I'd think. . .

 

[Marconi]

I know you are working with modeling software, but by what mechanical change would you fix the excessive mast currents on a real antenna. It must have a mechanical equivalent to have practicality, I'd think. . .

Well Homer you're right. I disconnected the mast from the antenna at a point where I found the least amount of current flowing on the rest the mast below the hoop. Then I looked for the best point to isolate. My idea was to find a point that showed the best balance and magnitude for the currents in the top element as compared to those currents in the bottom element. I think the better balance in magnitude there is in a 1/2 wave radiator...the better the model. And, I think these models tend to demonstrate that. I used an arrow at these points on the models so folks would be encouraged to compare the differences that I saw with the models.

On a real antenna I would try adding something in place of the isolated space that was non-conductive, but useful in keeping it erect. Of course, in such a real world case you would still have a coax, and I think that alone would tend to reestablish the current path and woud also need to be fixed. So, one would need to add a suitable choking device, that would hopefully produce similar results to the model.

If I could model a choke I would, and then add the coax and see what happened. Modeling is not the be all, do all in antennas, it's just a tool to easily test ideas. If I could physically do the work Homer, I would try to test some of my models and see. Isn't that basically what you do? The only difference being, I make a little model and you make the real thing.

My attempt here was to try and demonstrate what might be going on with this antenna in the bottom. I just had an idea and I test it, sorta' like I imagine you do. I don't really have any expectations for the models to be perfect when I start. I'm mostly just curious to see how they respond, and if they might reveal some trends I can recognize or test.

I would have never had the though I would see the "GainMaster choke affect" with this A/P model, but I think I see that at work now, and I think these models may suggest that. I think I got the idea from Bob some time back, and now I think he was on to something. I can't remember, what he said he expected in do so however.

Maybe you could test this idea on your A/P one day, and see if you can detect anything. Frankly I don't see much if any advantage by isolating or worrying about these currents, but that is not what I was trying to do.

I've been wrong before.

 

[HomerBB]

Ok. Sounds good.
So what the model shows is the need to isolate the mast 3" below the loop?

You may provoke me to get the AP up into the air again . . .

 

[Marconi]

Ok. Sounds good.
So what the model shows is the need to isolate the mast 3" below the loop?

You may provoke me to get the AP up into the air again . . .

No Homer, I'm not sure where your isolation should be placed, but I think it should be somewhere near the bottom of the loop. My model shows the following point worked out the best. I started with the end of wire #45 right even with the bottom of the hoop. I added an inch and the gain got a little better and the current at the bottom improved relative to the current in the top. I described this earlier.

I kept increasing the length of wire #45 as long as the gain and current balance in the antenna view improved. Everything started to go the other way at some point, so I just backed up to the previous length, and I ended up here:



If you'll look a the current flowing in the hoop on a previous image you'll see the high impedance field, in red, appears as a very small area around in the coil area, so I assume the choking device needs to be nearby, but maybe not right in that high energy field in order to do its work. At first I thought wire #45 needed to be a little shorter due to it being much a much larger tube than the radials, which should be at the end of a CB 1/4 wave electrical. However, I tried making it longer, and that seemed the way to go.

This modeling process I used might be similar to what you do with the coil on your 5/8 wave when you look for a tap point. I don't see much advantage in gain even doing the isolation bit to start with, but I did see some improvement in the current distribution with the model and I think that is always a best practice.

The hoop is designed to be at the end of a 1/4 wave, so I'd just try about a few inches to a foot below the hoop maybe, and see what happens. This project is specific to a fault due to the modeling software, but I'm not sure how much perfection you will have to experience in a real antenna or if you could even tell any difference. That is unless you see the antenna match or performance go to the dogs.

Good luck,

 

[Marconi]

Well Homer, I tweaked around on model #5 some more, and honestly I don't think isolating the mast at the hoop is worth the trouble, plus the problems associated with using an insulator.

The pattern is not quite as good and the currents are showing up on the mast, but if they don't cause any noticeable TVI or TVI is not a problem in a particular location, then the added radiation looks to be useful to me...as far as the maximum gain goes.

You do loose a little power in the secondary lobe too, but it looks like to me the A/P with a fully conductive mast is the way to go and that can improve reliability in the mount.

Sometimes common mode currents on the feed line and/or mast can be helpful.

 

[BOOTY MONSTER]

when you isolated it from the mast did you also eliminate the earth ground wire ?

 

[HomerBB]

Who knows what would really happen in the real world, so I may just try it soon. he AP is so light that changing the center mast pipe out for another that breaks at the 11.375" mark would not be a logistical difficulty at all.
As for TVI issues I have a wireless speaker that loves RF, so i could move it around until I found a point where one set up does or does not affect it.
We'll see. It's something to do beside watch TV.