Any Astro Plane Fans ?

[Marconi]

A Question:

On your models with the source attached to the center of the long radiator, is the top of the short side isolated from the top bracket or fully connected?

On the real antenna the short side is isolated from the bracket, The center coax conductor feeds the isolated leg, the coax shield attaches to the bracket and shorted to each other by way of the route through the hoop and both legs.

Would this make a difference in the models?

Feeding the long radiator side leads me to think the model may be producing results for a off-center fed dipole with cap hats on both ends.

Hey Homer.

Eznec does not require us to deal with making sure the FP is installed correctly like you imagine. It is not like we do in the real world Homer.

Homer your description is a good one, but the A/P is center fed and both the top hat and the bottom hoop "self cancel out," and they do not effectively radiate into the far field.

I know everybody hates to hear me say the word, "cancellation."

 

[bob85]

i can't believe i missed the source position up to this point eddie,
i was thinking only about currents,

imho putting it there makes it a dipole with no differential currents,

putting it in the right place makes it an astroplane, a different thing all together imho,
even though it may radiate about equal to a dipole.

 

[Marconi]

i can't believe i missed the source position up to this point eddie,
i was thinking only about currents,

imho putting it there makes it a dipole with no differential currents,

putting it in the right place makes it an astroplane, a different thing all together imho,
even though it may radiate about equal to a dipole.

Bob, you and Homer caught this old man fudging a little and I knew one day I would be asked to explain why I used this model with the FP at the base of the top radiator, rather than the one with the feed point at the top leg on the opposite side of the bracket from the main radiator where it belongs.

This antenna uses the mast like no other. With other antennas, I can add or remove the mast and see the antenna change some, but typically it does not go to heck in a hand basket...like it does with this antenna as I change from real Earth to Free Space.

I could maybe explain, but for the short story this was a compromise solution for me, but I realise now the compromised did change the antenna that was more dramatic than I first thought.

Bob, if you had not quizzed me, I may have never noticed this problem. The thing that I see right off the bat is the currents on the mast have changed, and maybe now you will see what is in your minds eye.

I post this change and its results over Real Earth and in Free Space below.

Thanks to Homer and Bob for helping me get this model straight.

 

[bob85]

eddie,
that is more like i imagined, the pattern shows the skew similar to the avanti patent,

the astroplane certainly uses the mast in a different way to conventional antennas,
the conductors relative diameters spacing and flare effects impedance at the feed-point,

there are certainly both antenna or common mode currents plus differential or transmission-line mode currents flowing in the transmission-lines formed by the mast and flared legs,

changing the flare won't do much to antenna mode impedance imho,
but it will change differential mode impedance seen in parallel
as you alter the flare or spacing,
the same way moving the cone elements in respect to the monopole changes impedance and resonance in the sigma4 without changing the physical length of the conductors.

thanks for the models.

 

[Marconi]

Bob, here is the A/P model in Free Space with the full mast left on. We don't see the fact that Eznec disconnect the mast from the ground, but it does so, and we can tell only by looking a the Tabular Currents Log.

Note that the TOA tilts down due to the influence of the full mast in the FS mode. Could this have anything to do with something else you read in the Patent...where they might have talked about tilting. I know that we have discussed the topic, but I don't rember anything beyond.

I noticed that I cannot see the source in the model...too much wire numbers in a bunch in the area. I will also post another image of the Antenna View blown up...so we can see the source location better.

 

[bob85]

im not sure eddie,
they only talk about the pattern tilting from about 5 degrees upwards if the mast is shorter than about 9ft below the hoop,

they do claim reducing the flare causes downtilt 10-15 degrees below the horizon and that it could be of use in certain circumstances.

 

[Marconi]

im not sure eddie,
they only talk about the pattern tilting from about 5 degrees upwards if the mast is shorter than about 9ft below the hoop,

they do claim reducing the flare causes downtilt 10-15 degrees below the horizon and that it could be of use in certain circumstances.

You reminded me of the last comment. After I fixed the models source point to the right leg, I did a free space model, and I left the mast alone. This model is what happened...the pattern was skewed a little by the long mast that in FS mode Eznec disconnected from the Earth. I will do more testing on the proper mast length tomorrow.

If you have decided what length below the hoop you will isolate, I will start there. Is that also where you will put your choke or ferret chokes or will you add it at the feed point?

 

[bob85]

eddie,
Id try my isolator 9ft or a little more below the hoop,
imho the legs will likely raise the resonant point of the mast a little,
choke at the bottom of mast,
about 36ft to the top bracket over average ground,
i can go about 16ft higher if i need to.

 

[HomerBB]

i

they do claim reducing the flare causes downtilt 10-15 degrees below the horizon and that it could be of use in certain circumstances.

Bob, this reducing of the flare, do you know whether that is pulling the upper part of the legs closer where the cross piece is, or reducing the diameter of the ring, or both?

 

[Marconi]

Bob here is what I get with your mast length and antenna height.

Just to be clear, if I got Needle Bender's idea right here, it did not fare well at all...with the isolation point at or very near the height level for the hoop.

 

[HotrailsStratPlayer]

I have owned a Sirio top one, and it worked very well it was a quaterwave antenna with gamma match, however the astroplane was listed as a 5/8th wave, now the top one was clearly a 1/8 wave element with a 1/8th capacity hat, my question is, is the astroplane also a quarter wave antenna, because if its radiating from the 1/8th wave section with a quarter wave groundplane it would be a quater wave with a different matching system to the top one, or am I missing something about the avanti Astroplane.

 

[bob85]

what did you do with the second model eddie,? its not clear how far down the isolator is,
why does the pattern look much better?.

 

[Marconi]

I have owned a Sirio top one, and it worked very well it was a quaterwave antenna with gamma match, however the astroplane was listed as a 5/8th wave, now the top one was clearly a 1/8 wave element with a 1/8th capacity hat, my question is, is the astroplane also a quarter wave antenna, because if its radiating from the 1/8th wave section with a quarter wave groundplane it would be a quater wave with a different matching system to the top one, or am I missing something about the avanti Astroplane.

That is good enough for me Hottrails. I see the Starduster the same...we can consider them as a 1/4 wave ground plane just as easily as a center fed 1/2 wave.

Personally, I find my 1/4 and/or CF 1/2 waves very good working antennas.

Thanks for your comments,

 

[Marconi]

what did you do with the second model eddie,? its not clear how far down the isolator is,
why does the pattern look much better?.

Maybe you meant as the top bracket Bob, as the one on top of the antenna at the top hat. I 'm not sure. Sorry I didn't explain better or ask.

The 2nd model is at 52' to the mounting bracket about 4' below the tip. I hope this is the top bracket you spoke about when you described your 36' and 52' feet heights. If not, let me know.

I did one like you suggested when you said you could possibly go 16' feet higher. Otherwise the models are the same.

 

[bob85]

looks like i will be making the mast telescopic again eddie,

i mean the bracket at the top of the mast,

im not sure if you modeled a 5/8 at the same tip height,
i found a 5/8 on 36ft mast you did, that's about the same tip height as the astroplane on 54ft of mast,

do you think moving the isolator from 1/4wave below the hoop upwards causes the pattern to tilt up as the patent suggests eddie ?