Any Astro Plane Fans ?

[bob85]

original astroplanes are stronger than they look Eddie,
my locals was up about 20 years on his chimney stack,

no i have not compared isolated vs not isolated on this antenna,
i isolated it because of how i think it probably works & don't have time to experiment right now,

i don't want current on my mast or feedline with any of my antennas, especialy if its current stolen from where it should be.

thanks.

 

[The DB]

I seem to recall Homer telling me that DB has a graph or something that shows his model with varying effects in mast lengths inside and projecting below the hoop. Maybe Homer or DB will give us a heads-up rather than us having to read volumes of posts trying to find this info.

I did this, it was pages and pages ago... Anyway, from Post 338...

This shows the difference in SWR between mast lengths from 100 inches to 850 inches long.

I thought I had posted gain over the same range as well, but the gain data I am finding does not have the same range of mast lengths. I'll have to look to see if I made a gain version of this data. I can also post the changes in X and R over this range...


The DB

 

[bob85]

Am I looking at the graph correctly, or am I seeing what I want to see because that's how I think it works ?

All of your models seem to show what I expect, am I looking through rose tinted glasses ?

NB's 1/4wave mast screws it up big time as I expect,

1/2wave electrical mast or multiples not connected to ground gives low vswr & low mast current,

odd 1/4wave masts give higher vswr & steal current from the upper 1/4wave,

DB
a mast length vs gain graph would be usefull if its showing low angle gain, gain up at 30 degrees is useless imho,

i take it that its freespace gain so we are only seeing the effects of the mast & not height above ground & the mast,

why does EZNEC have shitty low resolution graphics that get no better when you magnify them for a better look,
Is what we see on here what you see there on your screens when using the software or are we losing resolution when uploading/posting images,



thanks.

 

[The DB]

Am I looking at the graph correctly, or am I seeing what I want to see because that's how I think it works ?

All of your models seem to show what I expect, am I looking through rose tinted glasses ?

NB's 1/4wave mast screws it up big time as I expect,

1/2wave electrical mast or multiples not connected to ground gives low vswr & low mast current,

odd 1/4wave masts give higher vswr & steal current from the upper 1/4wave,

I did show this data before, and talked about exactly what you are mentioning here. I'm pretty sure I've done it more than once in this very thread. If it is what you expected, then it is either because you read my report and forgot you read it, or your expectations agreed with the modeling software.

DB
a mast length vs gain graph would be usefull if its showing low angle gain, gain up at 30 degrees is useless imho,

i take it that its freespace gain so we are only seeing the effects of the mast & not height above ground & the mast,

Here is a similar plot, except it is for gain. I didn't do it in free space like you requested, it wasn't necessary as I kept the antenna the same height above ground and only changed the mast length at said height. When running this I have to tell it the specific angle to calculate gain for, so this entire plot is the low angle lobe. Where you see gain spike down near the start, and again just below 550 inches, in both of those spots, and only those two spots, was the low angle lobe not the dominant lobe.

The DB

 

[HomerBB]

So the best gain (at what angle?) is with a 3/4^ mast from feedpoint or bottom ring?

 

[bob85]

DB,

i have thought the astroplane worked in a certain way for years not just recently, me & Eddie talked about astroplanes years ago,

i don't read every post in these long threads but i do try to read all your posts, i don't have the time or inclination to read the none technical posts & subjective reports,

your vswr graph is what i expected, the gain graph is not what i expected for low angle gain,
that's the first thing you showed me about the astroplane that is not what i expected,

you answered my question, you can set 4nec so it reports only low angle gain,
it would be nice if EZNEC did the same so we are not comparing apples to oranges,

you have the antenna high above ground to make the lowest lobe dominant like my antenna installs years ago,
Eddies models are closer to ground like my current install & always show secondary lobe dominates like a 5/8wave that's not high above ground,

its a bit apples and oranges again unless the reader already understands the effects of height above ground,

most people have a mast connected to earth which i think will invert the graphs 180 degrees, am i wrong?

while interesting its not practical for me to isolate so far below the antenna, i would need a super strong & expensive 2" solid fiberglass rod,

maybe Eddie will tweak his mast around the electrical 1/2wave point while looking at his current log to see if im correct about maximising current in the upper 1/4wave & minimising mast current,

i could be seeing what i want to see in his models.

i thank both you guys for your time & effort.

 

[Marconi]

why does EZNEC have shitty low resolution graphics that get no better when you magnify them for a better look,

Bob that sometimes happens when you're in the cheap seats.

You could ask. What image are you talking about? That might help get you some better results.

 

[bob85]

Homer
that's from the feedpoint / bracket,

Eddie,
all of them, look at post 432 isolated vs not isolated,
its as if we are only getting a thumbnail quality image, its very grainy & low resolution on my screen,
is that how it looks to you before you upload it ?

 

[HomerBB]

Because I used my homebrew wooden crank over mast to mount my antennas (except for temporary tuning as I built them) all of my installs were on nonmetallic mast until 5' above earth at which point the steel push up pole began. In such a case when I had an antenna mounted at 32' it was a coincidentally isolated mast at 27', especially if my coax choke was effective.

 

[The DB]

DB,

i have thought the astroplane worked in a certain way for years not just recently, me & Eddie talked about astroplanes years ago,

i don't read every post in these long threads but i do try to read all your posts, i don't have the time or inclination to read the none technical posts & subjective reports,

your vswr graph is what i expected, the gain graph is not what i expected for low angle gain,
that's the first thing you showed me about the astroplane that is not what i expected,

Ahh ok, thanks for the clarification. What, if I may ask, did you expect from the gain data?

you answered my question, you can set 4nec so it reports only low angle gain,
it would be nice if EZNEC did the same so we are not comparing apples to oranges,

you have the antenna high above ground to make the lowest lobe dominant like my antenna installs years ago,
Eddies models are closer to ground like my current install & always show secondary lobe dominates like a 5/8wave that's not high above ground,

The above images were at 75 feet above ground, that height was used because when I initially did the test I wanted as much mast length difference as reasonably possible. I did it again with the feed point 36 feet above ground just now and got this data.

SWR is the same, however, when it comes to gain, the spike up in gain isn't so high.

its a bit apples and oranges again unless the reader already understands the effects of height above ground,

most people have a mast connected to earth which i think will invert the graphs 180 degrees, am i wrong?

I just made two models for comparison, one with a mast that connects directly to earth, and one where the mast stops one inch above ground. Here, see if you can tell which one is which...

I expected the same as you when I made these models, but the software definitely disagrees with that conclusion. This is the first model I have seen behave this way, not that I did a lot of tests with a mast both connected and disconnected from the earth below. Perhaps this bears more research...

i thank both you guys for your time & effort.

Not a problem.

So the best gain (at what angle?) is with a 3/4^ mast from feedpoint or bottom ring?

Homer
that's from the feedpoint / bracket,

Bob is correct, the mast lengths in those charts are from the feed point/bracket.


The DB

 

[HomerBB]

The angle was best at 11°, 10°..?

 

[bob85]

DB,
i cannot tell for sure which is grounded, maybe if you had current turned on rather than phase it would be easier,

saying that i expect current phase to shift when connected to ground which does not seem to be the case with those two models,
did you use very poor ground ? deos your software not see 1" as isolated ?

i expected 1/2wave or multiples thereof to have a high end impedance low mast current & low vswr,

i expected odd 1/4waves to have higher mast current less current in the upper 1/4wave & higher vswr,
maybe higher gain but not at low angles.

 

[Needle Bender]

...NB's 1/4wave mast screws it up big time as I expect,... ...thanks..

EEEEEEEEENNNNNNNG! WRONG! - But thank you for playing!
- You guys remember that Jim Carrey line?
lol

Anyway, Bob I don't know where you came up with that but I've NEVER advocated ANY mast, not an inch, not a mile & nothing in-between.

When I get my AP back (it's still 165 miles away) I want to hang mine with rope ("in free-air") and pull the coax off at an horizontal with chokes, probably three or four CMC chokes, one about every 6'.
- But I've NEVER advocated a 1/4 wave mast.

I spoke with a local CBer last week who had a, "funny looking antenna, 20-30 years ago with an X on top and a ring at the bottom and was shaped like half an hourglass but it sure worked good until a guy from out-of-town offered me $200 to sell it to him, so later that same day I was $200 richer."

As we talked about it he said he had it installed on a 10' - 12' long 2"x 4" which he lag screwed to about a 15' tall tree stump in the back yard, with the coax taped to the top of the 2"x 4" and then pulled over to the peak of the house roof.
He said his SWR was "Flat" and that he used it from the top of the band to the bottom with his old 2950 and it worked "a lot better than the A99" he replaced it with.

...and was anyone listening when Homer posted that his was mounted on a WOODEN tower with a coaxial CMC choke?

Because I used my homebrew wooden crank over mast to mount my antennas (except for temporary tuning as I built them) all of my installs were on nonmetallic mast until 5' above earth at which point the steel push up pole began. In such a case when I had an antenna mounted at 32' it was mast coincidentally isolated at 27' especially if my coax choke was effective.

I also don't accept the modeled patterns which look a lot like a 5/8 pattern with high and low lobes.
The reason an AP would work as well as the anecdotal reports claim, I believe, is because it's effectively an efficient center-fed 1/2 wave dipole with much of the gain of a 3/4 wave, and shouldn't have more than a single current lobe pattern if installed well above ground,
- and in having no 2nd or 3rd lobe angles, it won't suffer from conflicting lobe angle cancellation at varying distances.

It's been a fun read, but I'm fairly certain I'll get the same results as Homer & the local Op when I suspend mine from non-conductive ropes or lines well above ground, and pull the coax straight out at an horizontal angle, out and away from the lower AP body. a good 1/2 - 3/4 wavelength before coming back down vertically to the ground, and with a CMC choke AT the feedpoint and about every 6' from there out.

Oh and do you recognize this rare find in the back of me trusty, rusty & crusty ol' truck bed last night:

 

[The DB]

DB,
i cannot tell for sure which is grounded, maybe if you had current turned on rather than phase it would be easier,

Actually, no, current looks very similar between the two just like phase does. I'll have to show you later when I get back. Even if I change the height of the antenna, and by extension the length of the mast, it does not seem to change. One thing to note is the currents on the mast are very low no matter what I do, so that may be a factor as to why this is happening.

saying that i expect current phase to shift when connected to ground which does not seem to be the case with those two models,
did you use very poor ground ? deos your software not see 1" as isolated ?

i expected 1/2wave or multiples thereof to have a high end impedance low mast current & low vswr,

i expected odd 1/4waves to have higher mast current less current in the upper 1/4wave & higher vswr,
maybe higher gain but not at low angles.

I used moderate ground. Even with poor ground I would expect to see much more of a difference than I am seeing with this model. This is new territory for me as well as I am just seeing this for the first time right now. I did check to make sure that a wire that ends at ground level is considered attached to the ground, and that is set. I will have to consider this. Maybe Eddie can confirm this for us when he gets a chance?

I think the low currents in the mast irregardless of its length goes back to that "blue line" discussion from pages ago, the further we were away from an optimal length mast the more currents that were flowing in that wire. I have shown in a previous post that it appears to be stabilizing the currents in the mast, and by extension the effects of changing mast length in the antenna, among other things. That was this post.

The angle was best at 11°, 10°..?

I am curious as to why you are asking about this.

The lower mounted antenna which is mounted at 36 feet, the angle of peak radiation is at 12°. The other model, which is mounted at 75 feet, is 6°. In both cases it doesn't matter how long the mast is, the angle of radiation for the low angle lobe stays the same, as it should.


The DB

 

[HomerBB]

I was asking sinply because of your answer, and curiosity. The higher height above earth the lower the TOA, as expected, however, if the primary gain lobe were at 30° then I certainly wouldn't want to mount it in a fashion that put best gain there. UNLESS I were wanting to talk only to Cousin Vinny in Jersey.