Any Astro Plane Fans ?

[HomerBB]

Thanks for all the replies. Very interesting . . .
I would like to see the outcome of both DBs models, and of NBs real time experiments.
I do not model, as all know, so I have had to rely on those who do, but I do love the the AP, a love based on my real world experience with it, so I am looking forward to both outcomes.

 

[HARDROCK]

NB . you can email w8ji@w8ji.com he can straighten it out.

73

 

[The DB]

DB
can we see the patterns for the above models,
with the mast isolated up at the ring where NB suggests,
isolated 1/4wave below the hoop & 1/2wave below the hoop,

thanks

Sure, here, then a few notes.

The green plot is choked at 104" (1/4 wavelength) mast length, or a little under the hoop. The red plot is 104" below that one (1/2 wavelength mast length), and the blue one is 104" below that one (3/4 wavelength mast length).

I want to make a note on the blue pattern, its AGT was high, which basically means it is off a bit compared to the other plots. I tried to fix it but I could not get it dialed in like the other models. A high AGT is known to sometimes over-report gain, so its gain may not actually be that high compared to the other models.

Also, I did an extended test similar to the SWR, Impedance, and Gain info posted above. Once you get past that SWR spike that is near the 1/4 wavelength of mast/feed line the model shows, SWR doesn't raise above 1.5 no matter the mast length, tested to over 2 wavelengths long. So essentially, if it is to short you will have trouble tuning, but longer masts/feed line don't seem to have a major effect on tuning, and gain is mostly consistent as well.

I'm not entirely sure what to make of that yet... Will need to play with the model some more...


The DB

 

[HomerBB]

And,
1. A metal mast with coax 90° straight out from the bracket feedpoint,
2. No mast (isolating non-conducting mast) with coax 90° from feedpoint, and
3. No mast, no coax, if possible.

Just askin' cause I like models and real world. Sorta like watchin' 'em walk the runway then goin' home with the kid's mama.

 

[The DB]

And,
1. A metal mast with coax 90° straight out from the bracket feedpoint,
2. No mast (isolating non-conducting mast) with coax 90° from feedpoint, and
3. No mast, no coax, if possible.

Just askin' cause I like models and real world. Sorta like watchin' 'em walk the runway then goin' home with the kid's mama.

Let me make sure I have this straight. For 1, you want the mast going straight down, and a feed line that comes out 90 degrees from the feed point?
2 is the same as 1, except the mast doesn't conduct, like fiberglass (or in modeling I just remove the wire)?
And 3 is just the antenna with nothing?

For 1 and 2, how long of a feed line do you want me to use going straight out from the feed point?

Also, NB said he was going to use an appropriate choke, I'm guessing at the feed point. Should I factor that in somewhere as well?


The DB

 

[HomerBB]

Let me make sure I have this straight. For 1, you want the mast going straight down, and a feed line that comes out 90 degrees from the feed point?
2 is the same as 1, except the mast doesn't conduct, like fiberglass (or in modeling I just remove the wire)?
And 3 is just the antenna with nothing?

For 1 and 2, how long of a feed line do you want me to use going straight out from the feed point?

Also, NB said he was going to use an appropriate choke, I'm guessing at the feed point. Should I factor that in somewhere as well?


The DB

I dunno. Use your imagination on the choke positions and feedline. I just wanted to see how the antenna alone looks, how a conducting mast with NBs idea of 90° feedline looks, and with the 90° feedline and non-conducting feedline would all model referenced to the other models you're doing. Then we could have those to reference the real world impressions NB gets.

 

[Needle Bender]

Hmmmm, guess my post was lost in the wind & waves

I'm not going to struggle with rewriting that long-arse response, suffice it to say that enough has been said on the choke subject.

I plan to support the AP with non-metallic line centered between a couple trees that are around 80' apart and I'll pull the coax off horizontally with a 5T x 4.25" current choke only inches from the feedpoint, then another @ 6', 12' & 18'.

There should be at least a full wavelength between the AP and either tree so I don't expect much in the way of pattern skewing because of them.

There will be nothing hanging from, nor attached to, the AP U-bolts.

 

[Marconi]

Needle Bender, if you left your post while creating your text and then came back to the thread and your post was gone...I think you can do a refresh and the text might pop back up in your post reply box.

 

[The DB]

I made some adjustments to the model, namely I modified it to match the dimensions to the charts that Homer used when you made your pvc version, I also modified it to be aluminum. I'm surprised that the origional model made by ghz24 wasn't already to spec... Not much changed when it comes to results so I guess his model was close enough...

The mast length that gets the lowest SWR (1.02), and very close to resonance, is 217 inches. For number 1 below the mast that was used was this length as it appears to be a best case scenario for the actual antenna.

I could put some new charts up, however, they aren't that different from the ones posted above, they follow the same basic patterns...

And,
1. A metal mast with coax 90° straight out from the bracket feedpoint,
2. No mast (isolating non-conducting mast) with coax 90° from feedpoint, and
3. No mast, no coax, if possible.

Just askin' cause I like models and real world. Sorta like watchin' 'em walk the runway then goin' home with the kid's mama.

For 1, no significant change in gain, their is noticeably less than 1 db difference in overall gain no matter the length of feed line used, minimum length modeled is 1/4 wavelength. The worst case scenario (which was 1/4 wavelength), the pattern is not exactly omnidirectional, it is more of an oval with about 1.5 dB difference between its peak gain vs its side gain. The peak gain in both directions that is broadside to the feed line. The SWR is slightly higher, but still under 1.5.

For 2, no matter what length I used, SWR was between 3 and 4, this could likely be tuned out with minor adjustments to the antenna itself. If using a 1/2 wavelength multiple for the feed line their was no real change to the pattern, but odd 1/4 wavelength multiples produced oval patterns like number 1 above.

For 3, gain went down some, from the 6 dB range to the 5 dB range, SWR is 3.8. Perfect omni pattern.


The DB

 

[HomerBB]

Any conclusions based on your .models?
Initially, it looks/sounds like dipole behavior with CMC on the feedline in #1.

#2 seems to reveal its mast dependency, as debated. I think the obvious indication is this antenna design is a radiating matching network in its total parts similar to the other coned/basket design antenna, but more so in its contribution to the radiated energy. Of course, remove the skirt and this antenna just goes away and becomes what it likely is, an center fed vertical dipole better suited to vertical performance with a better positioned maximum radiated signal toward the horizon. Or so I think.
#3? No CMC? No mast coupling nor attenuation from the feedline. Poorer match without part of its tuning network - mast/feedline.
Maybe NB's real world experiment can tell us what happens in #1 & #2 on planet earth.. He can't do number 3 unless he figures out how to send and measure a signal from it without feeding it via feedline.

Maybe I'm just rambling non-sensically. . .

 

[The DB]

Any conclusions based on your .models?

This antenna isn't what I know a lot of people think it is. This antenna has several little things that are hidden in the design that come together just right to make this antenna work. If ever their was a combination of RF science and RF art, this antenna would be it. Honestly, this is my new favorite antenna to try and take apart what is going on. I wonder why I didn't dig in to it sooner..

Initially, it looks/sounds like dipole behavior with CMC on the feedline in #1.

I'm not sure. At one point, before I really looked at this antenna design, I thought that the mast and the upper vertical element were a dipole, and the loop was just a matching section. Then I examined the feed point and boy was I wrong. That idea went down the toilet when I saw that both the upper vertical element and the mast were connected to the same side of the feed point which makes that idea impossible.

#2 seems to reveal its mast dependency, as debated. I think the obvious indication is this antenna design is a radiating matching network in its total parts similar to the other coned/basket design antenna, but more so in its contribution to the radiated energy. Of course, remove the skirt and this antenna just goes away and becomes what it likely is, an center fed vertical dipole better suited to vertical performance with a better positioned maximum radiated signal toward the horizon. Or so I think.

It would take some tweaking, but I think it might be possible to get rid of the mast all together. I am not going to put a guarantee on this, their are just to many details I see in this antenna and the more I look at it the more I see. Using the dimensions that the antenna came in, yes, it would require something, be it mast or feed line, and the antenna design assumes it is going straight down through the hoop.

The antenna design itself is part of the matching network, so to call it a "radiating matching network" would not be inaccurate.

Remove the "skirt" and the antenna is two wires connected to the same side of the feed point going in opposite directions and nothing attached to the other side. If you could make it radiate then it would literally try and cancel out its own radiation...

#3? No CMC? No mast coupling nor attenuation from the feedline. Poorer match without part of its tuning network - mast/feedline.
Maybe NB's real world experiment can tell us what happens in #1 & #2 on planet earth.. He can't do number 3 unless he figures out how to send and measure a signal from it without feeding it via feedline.

Number 3 is only a theoretical construct no matter how you look at it. A mast is one thing, but it is impossible to make a feed line completely invisible to an antenna.

Maybe I'm just rambling non-sensically. . .

You wouldn't be the first, and I'm sure you won't be the last.

Perhaps this weekend I'll have a chance to type up what I see in this antenna.


The DB

 

[HomerBB]

Without me having any deeper understanding of the antenna, my thinking is you startout by seeing that the upper vertical with the cap hat, the mast, and the lower common skirt radial are all connected to the braid side connection with the opposing skirt radial fed at the top from the coax center conductor where it is isolated from the mounting bracket.

The last time I looked at a diagram showing currents on the antenna my memory seems to recall that the ring is an inductor, which would possibly explain why each side of the skirt does not necessary cancel each other out. The short skirt radial would be the tap on the inductor in such a case . . . maybe. Not deep enough into the right or wrong of this idea, and my memory is kinda fuzzy. The diagram is on an inaccessible hard drive.

 

[The DB]

Here is a close up of the cross brace area of the antenna. The basket area connects on both sides and the mast connects in the middle. The feed point is the wire with the circle. Current magnitude is turned on, and this area of the antenna is almost all red and pink, or namely at or near current maximums. Their is an exception to this, however...

Ignore the grey area, that is just because the model is near one of 4Nec2's limits, it is however, still within spec, their were no errors when running this model.

The blue shows that their is almost no current flowing on that wire. What do you make of that?


The DB

 

[HomerBB]

I don't know how you constructed the model, but it would be a mistake to electrically connect the short skirt downward vertical to the cross bracket. They are electrically separate there. The bracket only serves as a mechanical support for the short vertical. If you have that short side isolated from the bracket as it is then I wouldn't expect much on that side of the bracket. If not, then change it and see what happens.

 

[The DB]

So they are isolated. I didn't get that from the info I found on your build thread. Good to know.

The original model I constructed that from made by ghz24 had that connected already.

Also, with this image of yours the aluminum foil appears to be directly connected to the bracket on the side of the antenna with the vertical element, although I guess I can't be certain by it either, but I would have figured that you used an insulator line on the other side. Also on the chart they provided the side with the antenna that includes the vertical and cap hat their is no insulation. The only insulation I see on this image and that diagram is on the far side of the basket.

The DB