Any Astro Plane Fans ?

[bob85]

Homer,

I believe we already know why the astroplane performs well vs other antennas at the same tip height even if we don't understand exactly how it works,

imho needing the mast inside the lower portion of the antenna in order to have a good match is a big clue as to how its working,
having a current distribution that looks like a transmission-line is another,

there are some antenna truths that don't go down well in the CB world but can be verified with models that can point us in the right direction as to how an antenna could outperform a 5/8wave when mounted at the same tip height,

a 5/8wave / .64wave is nothing special,
is just a 1/2wave of what we want raised higher above ground by 1/8wave of what we don't want (out of phase radiation) steeped in years of CB advertising BS myth and sentiment,

go longer than .64wave in a single element & that out of phase radiation spoils the pattern so much that high angle lobes form & low angle gain drops,

outside of the CB world its known that an efficient 1/2wave has a little more low angle gain than an efficient 5/8wave mounted at the same tip height,

a 1/2wave at the same tip height shares the same height of current maxima & has no out of phase radiation,

hat loading the astroplane while maintaining the same tip height raises current maxima higher above ground by about 1/8wave,

that is the same advantage in height of current maxima over a 5/8 as the 5/8 has over a 1/2wave endfed at the same feedpoint height & without the out of phase radiation you get with a 5/8wave,

imho those two factors height of current maxima & no out of phase radiation more than make up for any losses inherent in the astroplanes design giving it a small advantage over a 5/8wave,

there is no need to ascribe any special properties to the astroplane, all it needs to do is act like an efficient 1/2wave,
raising current maxima is a bonus but not necessary in order to outperform a 5/8wave at the same tip height.

 

[HomerBB]

Thanks, Bob. Makes perfect sense. As you know, without any "scientific" proofs I have long time expressed my belief that the AP is probably just a 1/2^ dipole, one end shortened with a cap, the other a somewhat of a caged element. I said I simply looked at it from a visual perspective and saw that in simplicity. That certainly doesn't make me a Cebik, nor Orr, but it does give me an opinion.
I 100% agree in the 1/2^ advantage over a 5/8^ at same tip height. Not tp dredge up bad juju, but the V4k and S4 share that same distinction, I think (the difference for me is that I still found the V4k superior to my AP at same tip height). Yet, the principle prevails.
Why I say someone will figure it out is I am looking toward the educated modeling crew to settle the discussion.
So, to directly reply to the statement I offered about my antenna was always isolated from ground, the antenna always had a long metal mast extending from the mount bracket to more than 1/2^ below the ring, and always a coax choke at ~9' below the ring . I don't think this constitutes an example of this current discussion regarding the potential impact of isolation/no isolation, or mast length/no mast, etc. This is because my permanent setups lacked variables that were tested and/or monitored. I looked at performance at the same tip height, and whether a good antenna could be constructed with duct tape and plastic pipe.

 

[bob85]

Homer
i understood that you did not use a wooden mast on your astroplane, yes i was listening,

interesting your vector clone had the edge, that surprises me,

of course a well constructed j-pole sigma or vector has an advantage in height of current maxima over a 5/8wave on the same pole, they also don't have out of phase radiation & will outperform a 5/8 groundplane,

im not done with the sigma yet, its still my favourite antenna,

i will add radials to bring it more inline with the open sleeve article since the sigma does not have the groundplane of the open sleeve article i posted about,

seems like people missed Henry's model showing adding radials to the sigma can increase signal strength by up to almost 2db at 30 kilometers.

modeling does not directly tell us how something like the astroplane or sigma / j-poles work homer,

imho you need to understand things like current distribution & transmissionline theory & understand how to use the software,

you should also be able to predict what will likely happen before you make a change to the model if you understand the laws of physics that antennas and software operate by,


Thanks.

 

[HomerBB]

The comparison between the V4k I built and the AP that resulted in the impression I have of the superior performance of the V4k was done on a metal mast installed on the wooden crank over mast. The tops of each antenna were the same height, ~54'.
I do get much of the technical discussion, although, like you, I depend on others to do the modeling. I suppose I might have better said that I believe that anecdotal discussions are good only to the point of each person's story or experience/impression. So I anticipate the more objective input to the discussion the models may add.
Sometimes I press a point, or ask a question not because I am struggling with the content, but because it is easy to rush ahead in a discussion forgetting there may be some reading along trying to learn who are not yet at the level the thread is trending.
Hopefully I maintain an even spiritedness through it all. Perhaps I am also a slow learner.
As for learning to model... right now I just don't have the time. Thought I would, but . . .

 

[Marconi]

Eddie,

i meant alter the mast a little either side of an electrical 1/2wave to confirm or refute the mast robbing current from the upper 1/4wave when the mast is not an electrical 1/2wave or multiple,

your models seem to confirm what i think.......

Bob I think you would have been disappointed in the full results in my post #452. I say that because the match was not 1.20 SWR or lower and the patterns showed little to no difference in gain and angle as noted. I was working with new dimensions for the original Astro Plane from Tib and I was not getting good results with the model as I noted above. So, I looked up my model for the Old Top One and here it is below in Free Space for now.

If this isolated Old Top One shows you improved results and you can see that the details you consider of value or worth considering, then I'll do the model over real Earth. I won't change a thing in the process, except add the bottom section of the mast to ground.

Then I will check my tabular currents log and report what I think is suggested relative to currents on the radiator and if they are maximum attainable.

The first image shows the Average Gain Results which is near 1 and considered very good. I also made a closeup of the antenna and made the Source Data report using bold type for a better clearer image.

 

[HomerBB]

interesting your vector clone had the edge, that surprises me,

of course a well constructed j-pole sigma or vector has an advantage in height of current maxima over a 5/8wave on the same pole, they also don't have out of phase radiation & will outperform a 5/8 groundplane,

im not done with the sigma yet, its still my favourite antenna,

Why are you surprised?
As for the tadials added to the Sigma providing 2db of gain, that surprises me!

 

[bob85]

Homer
im surprised because if the sigma is just an efficient elevated 1/2wave the astroplane at the same tip height should not be notably behind imho,

the stock sigma lacks the groundplane of the open sleeve antenna article i made such a fuss about,

it was suggested by more than one source both more knowledgeable than me on antennas that it needs the groundplane in order to do what the open sleeve article says,

a couple of folk have claimed the cone model proves there's very little radiation from the cone,

imho the model of the cone on its own terminated with a dummyload is only showing radiation due to the conductors not been parallel,

transmissionlines don't radiate when terminated with dummyloads regardless of been mismatched or not,

the cone or the stub in a j-pole has high vswr on it & its not balanced with a dummyload,
its unbalanced and that's what causes radiation in transmissionlines & the stub of a j-pole,

im not surprised at all that the terminated cone shows very little radiation,

if you can increase signal as much as Henry's model shows its well worth doing,

the isolator i made for the astroplane will clamp straight to the base of my modified sigma.

 

[bob85]

Eddie,
I'm not disappointed by ANY model,

I'm trying to establish if how I think it probably works could be true by predicting what will happen when a certain change is made such as having a mast that is not an electrical 1/2wave with high end impedance,

the conductors around the mast electrically shorten the mast as do the radials of the sigma as we sweep them towards the monopole so how do you know when you hit 1/2wave electrically?

I think its feasible to look at the current at the top of the mast and the base of the upper 1/4wave,
if I'm right, when mast currents are minimum upper 1/4wave currents should peak,

am I wrong?, I'm not sure because I can't make models at this time,
I started from the other side, trying to learn what and why currents flow in certain places, transmissionline theory etc,

if you don't understand what makes transmissionlines radiate or what the current distribution is on a gainmaster you won't get anywhere with your ideas of how antennas work,

I rely on you guys to do the models,
don't for a minute think me getting something wrong pisses me off, or that like some on here I think I'm always right and cannot accept what the models tell us if it does not fit my paradigm,

that's a recipe for staying retarded on practically everything like AMPOWER.

Look at it like when I'm wrong I learned something new,
we know it works on the laws of physics, we just need a better understanding of those laws.

 

[HomerBB]

Plenty in your reply to respond to, but I'll say one thing for the moment.
Despite the many different voices telling me it shouldn't have happened, my experience with my V4k clone was that I got out and received farther over our terrain better than any other antenna at same tip height
(It became unpopular to say so, yet it remains my experience). Up to 25 miles farther. The AP was better than the others with that exception.
Maybe my clone was different in some ways, but I couldn't say.

 

[bob85]

That's my experience too Homer,
i would not say 25miles further but i could not talk to people on the east coast on the i-10k that i could talk to every evening on the modified sigma mounted on the same pole,

locally the difference is small,

 

[HomerBB]

I understand the differences can be different in different localities. I know I spoke with folks on the V4k I had/have nerver spoken to before or since flying it.
If ever I get the chance to experiment again over long low terrain I'll see whether it was a fluke.
Gonna look more into the radials thing.
A link for it?

 

[Marconi]

Eddie,
I'm not disappointed by ANY model,

Bob, I don't want to get off track with my comment "...you would be disappointed in the results..." in my posted overlays in #452. But, I remember you commenting a while back that my AstroPlane models were showing 60+ ohms of impedance and the match was not 1.20:1 SWR like you were getting with your original A/P. It was a new model and I have not worked with it.

Along with the overlays I also produced the currents and I figure if you were disappointed in the SWR...whatever the currents showed us...you could correctly question such results. That is why I only posted the overlays which showed there was little to no difference in the patterns when I made the antenna part of the mast longer by 12" inches in 3 iterations for the idea. This is a short range compared to DB report of similar effects...but this is what I thought you were looking for.

So, I dug out the model of my Old Top One and posted the Free Space model to show the Average Gain and a near perfect match to boot.

I was thinking, if I then changed the mast length like I did above with my AstroPlane model in post #452, you might feel better taking a look at the currents report...which is 6 pages long and showing the currents and phase for every segment in the model. Then you could check out if there was a difference in the currents that really made a difference. I mentioned the difference I saw were fractional at best and I don't expect that to change if I do the same with this model of the Old Top One.

Then all I have to consider is if you have any confidence in the Old Top One being a fair equal of the original AstroPlane which has modestly different dimensions.

I hope this is clear.

 

[Marconi]

Gonna look more into the radials thing.
A link for it?

Homer, I made a model of this idea without any real understanding of the model that Henry reported. I read his claim and saw his graph, but I did not see any model, just a graph of some results. I'm not criticizing the report, I'm just saying I saw no model to try and duplicate...so I can't be sure of my model. I will post it in another post.

I can't be sure, but I think Henry used a feature in Eznec Pro 4, that DB used the feature in 4Nec2. DB posted some of his results which looked impressive, but I also recall Henry giving DB a caution in the use of the feature as well. I have seen no more such modeling.

 

[Riverman]

32 pages and counting.
Bet the guys at Avanti never thought their little antenna would generate this kind of debate. It would be interesting if one of the original designers came across this thread and told us what their thoughts were when they designed the A/P.

 

[bob85]

page 41 Homer
http://cb-antennas.com/wp-content/uploads/2013/12/Sigma-IV-1.01-Jan-2015.pdf