ASTROPLANE best vertical antenna ever?

bob85 said:

Eddie,
can you look at the current log to see if current going into wire 1 is equal to the sum of the currents in wires 4 & 5

if it is i would say its acting similar to a 2 radial starduster,
not sure how with the hoop at the radial tips but thats what it looks like to my eyes.

Click to expand...

I can print out the Currents Log and post it as a PDF file, in case you want more details. The model has 163 total segments.

I took the readings for just the 1st segments in each of these three wires, #1, #4, #5.

#1 = 0.83024 (A)

#4 = 0.43293 (A)
#5 = 0.4323 (A)
______________
------0.86523 (A)

Let me know if you think you want to add all these values together for all these segments and I'll post it. There are about 60 wires.

Here is the antenna with no choke on the Feed Line. Take note of the red line for current on the FL compared to the model with a choke.

That's not far from equal current in the upper 1/4wave & lower 1/4wave Eddie,
slight error somewhere possibly but its close,

the way its setup its acting similar to a 2 radial starduster,

i would expect adding the 3 currents (radials & coax) to also equal the current flowing into the upper 1/4wave.
you can see the current on the coax you added has been stolen from the radials,

i dont think you can choke the coax to stop current flowing if the radials were not providing an alternative current path,

its not broken yet but i think it will break when you add the mast & impedance drops,

a real astroplane has terrible vswr without the mast, its not so good just having skinny coax acting as the 3rd conductor either,
you need to respace the radials for skinny masts/coax on a real stroplane to get vswr back where it should be,

the patent tells you it works with just the coax but they don't tell you only if you space the conductors correctly.


Thanks for the models.

Eddie,
i posted an article explaining antenna mode & transmission-line mode currents in the sigma4 thread,
heres another article https://docer.pl/doc/sss0v80

and the part i find interesting,

"However, at the resonant frequency of the sleeves, the impedance of the central monopole is that of an end fed half-wave monopole and is very high. Therefore IA is small. If proper element diameters and spacings have been used to match the transmission line mode impedance, ZT, to 52 Ω; then IT, the transmission line mode current, is high compared to IA. This means that very little current flows in the central monopole above the tops of the sleeve elements, and the radiation is mostly from the transmission line mode current, IT, in all three elements below the tops of the sleeve elements".

i hope this article clears up what i mean by

antenna mode impedance (ZA) impedance of astroplane loop without mast

antenna mode current (IA) current flowing into antenna mode impedance

transmission-line mode impedance ( ZT ) impedance seen in parallel with ZA when you add the mast

transmission-line mode current ( IT ) current flowing in the transmission-lines you create when you add the mast to the astroplane that flow as transmission-line mode currents,

thats why i choose a properly isolated electrical 1/2wave mast,
& why you can have an odd current distribution where you have transmission-line mode currents on the radials and on the part of the mast inside the cone with all 3 conductors radiating & much less current below the hoop,

when you see that effect as DB does when he adjusts the mast a little longer than 1/2wave he's resonating the mast which must be a little longer than its freespace electrical length for resonance,

that maximises mast antenna mode impedance & minimises antenna mode current in the mast,

then most of the current is flowing in the 1/4wave unbalanced radiating transmission-lines as transmission-line mode current,

if you extend the mast to 3/4 wave its not as unbalanced at the end of the lines,
ZA of the mast goes down & current is maximised in the mast above & below the hoop,

thats not what i want at all..

Houston we have a problem,

DB
are you sure that odd 1/4wave masts show the same strange current distributioon on the mast that the 1/2wave mast produces?

if that's true then its not working as i imagine unless you had the 3/4wave mast grounded so the low impedance is transformed through odd 1/4waves to have high end impedance like the 1/2wave ungrounded mast.

what am i missing ?

bob85 said:

Houston we have a problem,

DB
are you sure that odd 1/4wave masts show the same strange current distributioon on the mast that the 1/2wave mast produces?

if that's true then its not working as i imagine unless you had the 3/4wave mast grounded so the low impedance is transformed through odd 1/4waves to have high end impedance like the 1/2wave ungrounded mast.

what am i missing ?

Click to expand...

Just to make sure we are on the same page, the mast I was using in said model does not connect to the earth, it was hanging out in space. The length measurement I was referring to assumed that the mast ended at that point in space below the antenna via choking or some other isolation method. If it was connected to a "perfect ground", said effect should shift by 1/4 wavelength to a current node, however...

I also remember some strange things happening to the currents on the mast when it was connected to the MiniNec ground at some lengths, I don't recall the specifics. I don't know if this was because of the antenna design itself, or one of the (way to many) flaws in the MiniNec ground algorithm, or perhaps, now that I think about it, possibly a combination of both?

Unfortunately, I checked, I don't have any of the models from before, none of them were in one of the backups I was able to recover, so I would have to build the model from scratch again to play with it...



The DB

Alexis Mercado said:

It is the Tagra BT-101 manufacturer who states his antenna is a 5/8 wavelength antenna.

Click to expand...

Somehow I missed this or I would have responded sooner.

You actually trust the words of a manufacturer? In this case a manufacturer that at best copied someone else's design?

If you want me to consider anything Tagra says about this antenna, please show me something that they have written that is more technical than their marketing pitch. I don't recall reading anything from Tagra on this antenna, so its entirely possible I missed something, so if you got it I would love to see it.

Don't get me wrong, I'm glad someone is sill making and selling this antenna. But being able to build this antenna does not imply that you understand how the antenna works. To build this antenna, all you need is someone who can follow a blueprint that is freely available online. Hell, one awesome member of this forum has been known to make a version of this antenna out of PVC and aluminum tape and it worked fine for him, and the others he built them for.

Seriously though, there are things stated in the Avanti patent that have been shown to be inaccurate, so at best I, personally, would try and confirm what anyone, including people who are making this antenna today, say about this antenna independently.

If you want to believe that this is a 5/8 wavelength antenna, go for it, I don't particularly care. In the end, what does it matter if it is one wavelength or another? Get the various different length antennas to the same tip height and watch the differences get so small you don't even notice them. Actually, the Astroplane was designed to outperform other antennas mounted at the same tip height... This is actually stated in the patent...


The DB

bob85 said:

Eddie,
i posted an article explaining antenna mode & transmission-line mode currents in the sigma4 thread,
heres another article https://docer.pl/doc/sss0v80

Click to expand...

Bob, the "docer.pl/doc......" link above does not open for me.

I found the following link in your thread, "Avanti Sigma4: An Alternative View Point," and it does not work either. Is this the other article one you mentioned above?

bob85 said:

heres an article on how to build one for 2mtrs, http://k6mhe.com/files/ssfm.pdf

Click to expand...

.

No Eddie, that's the skeleton sleeve fed monopole, a 3/4wave conductor with 1/4wave sleeve,
it does have the same antenna mode & transmission-line mode currents but,

the end of the ssfm transmission-line or sleeve if you prefere is looking at the high end impedance of the 1/2wave above it & air so its not severly unbalanced & the radiator is resonant 3/4wave so it has low antenna mode impedance high antenna mode current in the radiator above & below the sleeve,

the skeleton sleeve will still radiate a little with common mode current due to the unbalanced termination at the top of the sleeve just like a j-pole,

the link i posted explains how the currents are divided into antenna mode & transmission-line mode currents,

DB said he's never seen that odd current distribution on other antennas,
He will see the effect if he makes a model of a 1/2wave with 1/4wave sleeve spaced correctly & the whole shebang is brought to resonance,

im not claiming the astroplane is just as i describe,
imho its a modified version of it, two current modes in parallel, two modes of radiation with IT been the dominant mode,

i sometimes ask myself why do i keep going down the Avanti rabbit hole when i never made an antenna model in my life, i don't know why,
i admire you guys for sitting there inputting data segment by segment,
that would drive me NUTS, but i like reading what smart folk tell us & doing my own experiments to prove it to myself,

Thanks to you and DB and Henry HPSD for putting up with me over the years, & making models i can't make.

DB you have me baffled with impedance going up when you adjust the mast to 3/4wave ungrounded,
id expect vswr to go up but impedance to go down at the feed-point with odd resonant 1/4wave lengths ungrounded,
because antenna mode impedance is seen in parallel with the transmission-line mode impedance,
i don't understand how that can happen if its not grounded to invert end impedance seen from the top.

i never heared of a situation where lowering an impedance in parallel with another impedance causes a rise rather than a reduction in overall impedance so im scratching my head at the moment,
there has to be a logical explanation but i don't know what that explanation is,

i need to do some more learning,

Thanks.

bob85 said:

i admire you guys for sitting there inputting data segment by segment, that would drive me NUTS

Click to expand...

Bob, don't be so hard on yourself. However, I understand your frustration. I regret you didn't take me up on us working together as best we could on an effort to learn to model. With your understanding of the science...I think you would have been excellent at modeling.

You won't believe me Bob, but IMO modeling is not exactly like you describe. I guess your idea above...about inputting data segment by segment, is as off the point as your idea that modeling has so many problems and errors in operations...that it can't be trusted for any good results.

Cebik, W8JI, and some others use it or other NEC designed software...and I think you respect the work of those two at least. Modeling is just a tool and folks mess up using tools all the time...just look around.

However, this is not to say that modeling is never tedious to work with in some cases, and the A/P is no exception.

I made a silly mistake in my models above when I attempted to place a feed line from the feed point side of the A/P models above. As soon as I fixed the error and added the mast back to that model it crashed...just like you predicted and DB has claimed too.

Eddie,
of course I respsect guys like w2du, Cebik, w8ji,
listening to those guys reduced my noise and eliminated multiple peoples rfi issues & incresed their signal strength a little,

they taught me about transmission-lines vswr transformation what makes them radiate what supresses the radiation, im still learning as i go along,

when you guys make a model that sort of agrees with how i think it should be its a good feeling since im coming at it from the opposite direction,

when it does not agree i want to know what im missing, is it my understanding thats off or is it an error in the model,

Im not an AMPOWER kind of guy that believes books & software are only for book smart folk & the real world is different,

you have taught me something i never would have believed at one time, that all cb verticals perform about equal once you get them at the same tip height,
they must be properly isolated but once you do that its is true they all do perform about equal,

i took book info to the real world, it works, NEC uses the same rules so it must also work,

i do think you need to understand transmission-line theory alongside been proficient with NEC,
otherwise you would not realise that the sigma4 cone terminated with resistors is only showing radiation due to the none parallel conductors or that the astroplane and other antennas with transmission-lines in their construction have two modes of current,

the free version of nec has too few segments for anything id be interested in & the pro version is way too expensive,
there are things i need that are much more important even more so now my circumstances have changed,

i don't need it to make my antennas perform as they should & it won't pay my bills,

i imagine it could be somewhat annoying when a guy ( me) who never made a model keeps poking his head down the rabbit hole like Elmer Fudd, i apologize for that.

Eddie
The first image looks like you put the choke at the wrong side of the feed-point to my eyes, is that what you did ?

The other images are too small to see whats going on.