Any Astro Plane Fans ?

[bob85]

i understand what you are saying eddie,

phasing at 1/8wave looks to have skewed the mast currents,

not sure if you tried it isolated with the source in the right place & the hat replaced by something closer to 1/4wave to put the two 1/2 in phase,

the old laptop is broke, i bodged it to make it work, i will see if i can get it running again.

 

[Marconi]

I think I've already done that. I so, I post up various models with isolation and no, and the source right and no.

 

[Marconi]

BTW, these models are all at 32' feet to the hub. I gave up on 18' feet when Steve told me his model was at a wavelength. That might be a wavelength for 10 meter, but it will be close.

I will also make the radiator a full 1/4 wave, with the same ideas in mind as these below and post later.

If this is not what your considering let me know.

 

[Marconi]

Bob here are the results of adding a full 1/4 wave radiator to the A/P model with and without isolation at 8' feet below the hoop. I also switched the FP between the two points we talked about on wire #10 at the base of the radiator, and wire #4 at the top of the down radial under the physical feet point on the antenna.

These antennas were all at 32' feet to the hub not at 36' like they show, so the results may be a bit better than noted here, and the RF on the mast I find could be bit worse as a result of being at 36' feet.

This may be better than I first thought when I was working the models at 18' feet earlier.

I also added my notes on this as a Recap of the results for both sets of models.
1. with the top hat on the model
2. with a full 1/4 wave radiator

NOTE: Bob this post was edited on Dec 28, 9:00am for a mistake I made on the height I noted on the models in error.

 

[Marconi]

Bob check out this collinear Starduster that is basically the same as the A/P model. See what I said about my SD'r...it does not look like a 1/2 wave like I thought. The only currents from it that are radiating into the far field is from the 1/4 wave radiator and the top 1/2 wave above.

When I first did my model for the A/P I was saw something similar, and I mentioned it on the forum I think, but that was my error. I also noticed how bad the match was.

If DB's model works just fine...I don't understand what I have here then. This might clear up after I have the chance to fiddle with its matching and make sure the phasing stub is good to go and is all connected good.

 

[bob85]

gain looks ok with the 1/4wave & isolated if the match can be adjusted for 50 ohms eddie,

looking at the starduster co-linear i can see the 1/4wave and upper 1/2wave are too long

thanks

 

[Marconi]

gain looks ok with the 1/4wave & isolated if the match can be adjusted for 50 ohms eddie,

looking at the starduster co-linear i can see the 1/4wave and upper 1/2wave are too long

thanks

I agree Bob the SD'r model is a bit long, and maybe the 1/2 wave above it, is too.

But, you liked the A/P with the full 1/4 wave and isolated...and it too is also a bit longer than I expected. I guess having the 4 wires I added above the A/P has some effect requiring the model to want to be a little longer. With the A/P I fiddled with the tuning and adjusted the radiator length and the phasing stub a bit and the model responded better that it did at first.

Since Steve told me his antenna is at 36' feet, I will try and fix the SD'r collinear model. I just posted it for you to give you a better idea of what I was seeing...that made me question my idea of what the SD'r is...a center fed 1/2 wave or a 1/4 wave ground plain.

When I first did this SD'r collinear, I recall thinking the antenna showed to be short, and now you say it is long. I'll have to check that out and let you know if I can improve on this model. Do you know why Steve picked the SD'r to model as a collinear?

I didn't spend any more time fiddling on this SD'r, because of the problems I saw with my original spec model was not showing the gain Steve was reporting with his original SD'r, and when I saw the radials were not radiating in phase with the radiator when I made it collinear with a 1/2 wave above it...so I gave up on it.

 

[The DB]

Do you know why Steve picked the SD'r to model as a collinear?

That is easy enough, when bob showed me the diagram it looked to me like a starduster with a collinear section...


The DB

 

[Marconi]

That is easy enough, when bob showed me the diagram it looked to me like a starduster with a collinear section...


The DB

Thanks Steve, I went back to look for Bob's EzBob's antenna view of his idea, and in the process of reading several pages of old posts I noted that you posted a response to the idea...suggesting that you saw it as a simple Starduster. I remember reading your post, but I just forgot.

I saw it, and thought he was playing with me, but I still saw it as a collinear A/P, and that is what I first worked on as a model...and I was not having any success until I fiddled with the tuning and I did have to make the model a bit longer than I expected.

http://s5.photobucket.com/user/ukmudduck/media/topsyturvey.png.html

I was surprised when you modeled a Starduster, so I asked Bob if he knew why. Have you modeled an A/P yet?

 

[The DB]

I was surprised when you modeled a Starduster, so I asked Bob if he knew why. Have you modeled an A/P yet?

Posted many pages ago...

Interesting thread. I have never directly played with an astroplane, so am taking the sidelines for the astroplane discussion.

I have not done anything when it comes to modeling an astroplane either. It is a different antenna, I'll give you that.

I am curious how the feedpoint connects specifically with that antenna.


The DB

 

[HomerBB]

DB, these images should give you the idea of the feedpoint construction of the AP. Mine is/was a direct coax feed, center conductor to the short side of the two lower radiators with braid to the bracket. the short side is isolated from the bracket, the long side, that is the side that has the radiator continuing upward toward the cap hat, is grounded to the bracket.

 

[The DB]

Thanks Homer. I wasn't sure if that is how the feedpoint was set up or if the vertical side was split...

So electrically we have a loop of a given length, likely electrically half wavelength, and a quarter electrical wavelength off of the top connected to one of the sides of the half wavelength loop. Reading above, the mast also plays a part in some way...

That is an odd antenna design...


The DB

 

[Marconi]

Thanks Homer. I wasn't sure if that is how the feedpoint was set up or if the vertical side was split...

So electrically we have a loop of a given length, likely electrically half wavelength, and a quarter electrical wavelength off of the top connected to one of the sides of the half wavelength loop. Reading above, the mast also plays a part in some way...

That is an odd antenna design...

The DB

DB, Homer's image shows exactly how the real antenna is fed, but when you model it we do not have to isolate the feed point...we just place the source in a segment as close as possible to the feed point, and the NEC software takes care of any isolation needed.

If you designed a A/P model with the end of this radial isolated from the mount and you set the source at the end of that radial, like I note in the attached images ...the model would not work as intended.

It is possibly a hard concept to understand, but that is the way Eznec works. DB, I assume the 4NEC2 works the same.

I added a print-out of my wires descriptions so that if you wish you can enter my data into your editor for the same data elements like I did with your file a while back.

You will have to added the setting for you model possibly, but this model is set over Real Earth, with average soil, using aluminum. Maybe this will help you get a little head start on building such a model...if this works for you.

So, Homer if you see what looks like a source connected wrong in this model...not to worry.

 

[The DB]

To my eyes, at least initially, it looks like a dipole (upper vertical element and the mast for both sides of said dipole) and a half wavelength loop (the "radials" and hoop area) in parallel with each other, at least as far as the feedpoint is concerned.

A quick and dirty model with a dipole and a half wavelength loop in the vicinity of the lower element of the vertical dipole shows gain over a center fed dipole. It was, however, very touchy when it comes to impedance, specifically the X variable, a change of 0.1 wavelength (10 millimeters, or about 0.4 inches on a 10 meter antenna) changed the X variable by about 150. I've never seen such a big change from such a small adjustment...

Note, this was a simply a model of the concept of a half wavelength loop in parallel with a center fed dipole. It did not even resemble the astroplane design and was more a proof of concept type model. It wasn't refined in the least.

Thanks for the details Eddie, perhaps I'll get a chance to put them in at some point and play with it...


The DB

 

[Marconi]

Thanks Homer. I wasn't sure if that is how the feedpoint was set up or if the vertical side was split...

So electrically we have a loop of a given length, likely electrically half wavelength, and a quarter electrical wavelength off of the top connected to one of the sides of the half wavelength loop. Reading above, the mast also plays a part in some way...

That is an odd antenna design...

DB, my virus software is giving me a warning that in one hour from now something is going to happen, because I need to change my password and everything I've done in the last week...was not successful in my making the necessary change. So, I may not be able to respond tomorrow if I loose my ability to connect to the Internet.

I'll get it fix or maybe I'll use my tablet, but I hate using that thing...I can hardly see and that is even smaller than this computer.

I don't think I see the A/P like you do. I see the currents on the radial under the feed point being out of phase with the currents on the mast. To some extent they cancel out, but not completely. I refer to the end of this radial as a tuning stub that is connected to an orbital 1/4 wave hoop at the bottom that transfers and changes phase over to the bottom of the radial leg on the other side. I see this process as end feeding this radial and the shortened top element with the top hat as a 1/2 wave resonant radiator where all these current on this 1/2 wave radiator are in phase, with a little difference in magnitudes it appears.

So, to me the mast inside the antenna and the tuning stub work off of each other, so to speak, but don't contribute effectively into the far field. If there is any net currents left over after cancellation between these to elements, and there will be, then this current is likely following in a bad way down the mast and/or the feed line. Just my opinion.

You are right, this antenna is strange, but in many ways is a bit similar to the S4 design IMO and is typical of what Avanti seems to do quite well when they built their antennas.