Difference in AstroPlane vs. New Top One per Eznec5

[Marconi]

nb, where do you see 3/4wave folded?, i have heared this idea before but never seen an explanation of where the 3/4wave is hiding,

if you go with a simple explanation ignoring transmissionline mode currents where do the antenna mode currents flow?

you could try feeding the antenna without the mast/feedline to test avanti's claim that the 50ohm comes from the transmissionline mode impedance.

Bob, I removed the mast form the model. I'm not sure if the 50 ohms comes for the transmissionline mode impedance (TLMI) or not, but the model sure goes to heck in a hand basket. The model will not even run in that condition.

So, I think you make a very good point, even though I don't understand exactly how you visualize the TLMI.

 

[Marconi]

i understand what you are showing us with the mast currents eddie,
im not sure what the + & - signs are meant to indicate since i see current on the outside of the radials in phase with the upper 1/4wave like a 1/2wave,
does a dipole have the same + & - either side of a dipole feedpoint in your current logs?

what happens to the astroplane when the mast/coax are removed from the model?

Bob, so that I understand better, how are you determining that the currents on the outside of the radials are in-phase with the upper 1/4 wave....?

To answer your question,

does a dipole have the same + & - either side of a dipole feedpoint in your current logs?

You can't tell the phase from the antenna images. That is why we have the tabular currents log, it notes the magnitude and phase sign for each segment in each wire and notes when the phase shifts. The image would be too crowded to indicate this much detail. I wouldn't object however if Roy provided an option to include an antenna view that showed a small + - along side of each segment in the model. But he does give us the actual data in the log so.....

IMO the plus and the minus happens in real the real world with RF, but in order for the MOM's program to report stuff, it has to freeze the images and data in time, that is probably why is described as MOM. The antenna software that Sirio demonstrates to us is better in this regard. It uses a simulator to describe in a real slowed down fashion how the currents are flowing and that is nice, and you can see in-phase in similar colors, and out-of-phase in different colors, but Eznec doesn't have such a feature.

With Eznec, you have to check the tabular log to determine the phase for each segment in a wire.

I sure hope I'm correct, and hope I made myself clear with my words.

Here's are examples of the current signs for a 1/2 wave vs. 5/8 wave, and it shows the out-of-phase cancellation in the bottom of the 5/8 wave, and no cancellation in-phase condition for the 1/2 wave, just as we might expect.

View attachment Bob's idea on phase.pdf

Bob, the A/P model does go to pot when I remove the mast, just as you imply.

 

[bob85]

i don't imagine much antenna mode current will flow in the radials been a 5/8wave loop fed with 50ohm coax,
your plot shows equal current magnitude in the same relative place on the radials not one radial delayed by the 1/8wave loop which leads me to the idea that its probably a radiating tapered transmissionline,

i imagine a similar radiation plot to a 1/2wave endfed with in phase currents along its length,
i don't see how it could work so effectively if the upper 1/4wave was out of phase with the lower 1/4wave.

 

[AudioShockwav]

Here you go Marconi.

http://www.worldwidedx.com/cb-antennas/61487-astroplane-up-testing.html

73
Jeff

 

[HomerBB]

I've just been looking at an old 2007, thread to refresh my memory of what has previously been said on the A/P subject. Look here, if you haven't seen it, you will be interested I think: http://www.worldwidedx.com/cb-antennas/26370-new-style-astro-plane.html

Thanks, I had read it some time back, but just read it again. Very interesting, esp this piece here:
post #39

This guy, Starduster, came on for a while and could model, and was building a really nice and durable A/P styled antenna, and was experimenting on the best design. He is the one that really got me interested in learning to model, but he disappeared and I hated that. He was one of the few that didn't just give us words. Like you, he really did some work and showed us. Check it out, he was doing some of the very same things that you just did with your A/P, and that is remarkable. Too bad it's such small print, and ignore my notes. I have no idea what most of that means any more. If you can read his bandwidth charts, you will note there are frequency mistakes in his list. I just fix them in my mind.

Yes, I remember that thread, and was also disappointed when he went off-the-air here on the forum.

Thanks to Jeff for locating the other thread.

 

[gamegetter]

Thanks, I had read it some time back, but just read it again. Very interesting, esp this piece here:
post #39


Yes, I remember that thread, and was also disappointed when he went off-the-air here on the forum.

Thanks to Jeff for locating the other thread.

Homer, that quote from LC from the patent helps substantiate the 1/2 wave claim we are thinking the AP is.

 

[HomerBB]

That's what I thought.
Although LC shiedaway from challenging the notions of the heavyweights who were speculating that it was some other wavelength antenna, he was, in my opinion, on firm ground with offering the direct quote from the patent that clearly stated the electrical properties of the antenna as opposed to other quotes that appeared to be stating the construction/mechanical characteristics of the antenna. Many antennas, esp mobiles, have conflicting mechanical lengths vs the electrical lengths that they operate at. . .
It appears to me that it is, according to the patent, a 1/2 wave antenna.
Hey, Doc, we are running low on nits . . . can you help

 

[Marconi]

That's what I thought.
Although LC shiedaway from challenging the notions of the heavyweights who were speculating that it was some other wavelength antenna, he was, in my opinion, on firm ground with offering the direct quote from the patent that clearly stated the electrical properties of the antenna as opposed to other quotes that appeared to be stating the construction/mechanical characteristics of the antenna. Many antennas, esp mobiles, have conflicting mechanical lengths vs the electrical lengths that they operate at. . .
It appears to me that it is, according to the patent, a 1/2 wave antenna.
Hey, Doc, we are running low on nits . . . can you help

Yep Homer, LC is a cool kind of guy and kept guys on their toes with some good, sensible questions and ideas.

i do not know enough to have opinions here, i just state what is in the patent sheet.

the patent sheet says two things that interest me here.

1. "the pair of CONDUCTOR MEMBERS are electrically connected at the lower level, and one of the CONDUCTOR MEMBERS is electrically connected at the upper level to the first conductor and to a PROJECTING CONDUCTOR which extends upwardly from that upper level. THE PROJECTING CONDUCTOR HAS AN EFFECTIVE ELECTRICAL LENGTH EQUAL TO THE LENGTH OF THE CONDUCTOR MEMBERS."

(caps used for clarification, not for "yelling")


2. "the electrical circuit of the antenna in fig. 2 is illustrated schematically in fig.5. DIMENSIONS A AND B ARE EACH ONE QUARTER WAVELENGTH IN ELECTRICAL LENGTH"


if you look at the diagram referred to, you can see that A is the top radiator with the horizontal radials.
B is the bottom conductor members, and the hoop.
not one of the conductor members, not just the hoop, but all three are included as part of "B".

see quote above.


again, i dont have any opinions, or interpretations, i believe that the patent sheet is quite clear about this.

my question to the antenna gurus here is this:
if the antenna IS a half wave antenna, then would the way it is fed make sense for a good match to 50 ohm coax?

loosecannon

Even though I can't find a suitable feed point match on the model's hub anywhere, the simple answer to LC's question above is so obvious to me...the 1/2 wave is center fed.

If I put the feed point on wire #3, where it appears to be on the antenna right above down radial #4, the match looks OK, but the model won't work too good or maybe even not at all, I just don't remember. My model works fine with the source (the feed point) located on the hub end of wire #4 only and is indicated by a small red circle. To my understanding the real antenna's feed point and the top of wire #4 is not even touching the antenna in an electrical sort of way, it is isolated at that point on a maximum current node, and only by connecting the hoop at the bottom does the connection at #4 and #5 come into electrical contact with the antenna at all.

Hope that is not confusing, but I was thinking guys might be interested in how that part worked. The whole antenna shows continuity at every point, and I think guys would wonder how it can be directly fed, I know I did the first time I got my hands on that one.

Again, there's a great quote from the patent on such matters, on column 4, lines 26-29, and here we might find the distinction that hides the mystique.

 

[W5LZ]

... sorry, this is my day off, no nits getting picked today. Maybe tomorrow.
- 'Doc

 

[HomerBB]

... sorry, this is my day off, no nits getting picked today. Maybe tomorrow.
- 'Doc

Shucks . . .:sad:

 

[Marconi]

Here you go Marconi.

http://www.worldwidedx.com/cb-antennas/61487-astroplane-up-testing.html

73
Jeff

Thanks Jeff, you da' man.

 

[HomerBB]

If I put the feed point on wire #3, where it appears to be on the antenna right above down radial #4, the match looks OK, but the model won't work too good or maybe even not at all, I just don't remember. My model works fine with the source (the feed point) located on the hub end of wire #4 only and is indicated by a small red circle. To my understanding the real antenna's feed point and the top of wire #4 is not even touching the antenna in an electrical sort of way, it is isolated at that point on a maximum current node, and only by connecting the hoop at the bottom does the connection at #4 and #5 come into electrical contact with the antenna at all.

Yes. the center coax conductor is isolated at the top of wire 4, and the coax braid is not. It is grounded to the mounting strap/hub.
That to me is a classic method of building a common 1/2λ dipole. . . split the coax to each of the dipole 1/4λ poles, no?

You'll notice on Starduster's model the connector is isolated to the center conductor for contact to wire 4, but the shield is directly connected to the hub via the bolts holding it together.

 

[Needle Bender]

Read the patent, read both strands, found someone I agree with:

that's because you're looking at a top loaded 3/4 wave vertical wherein the bottom 1/4 wave has been folded. if you "unfold" the bottom 1/4 wave (sans the upper bracket) the center conductor and the shield connections would be a 1/2 wave apart from one another.

 

[HomerBB]

needlebender, I know you're trying to say something here, but it eludes me what it is.
The post quoted makes no sense:

that's because you're looking at a top loaded 3/4 wave vertical wherein the bottom 1/4 wave has been folded. if you "unfold" the bottom 1/4 wave (sans the upper bracket) the center conductor and the shield connections would be a 1/2 wave apart from one another.

Everyone knows a folded dipole if unfolded will be physically 1/2 wave, but folded back on itself it is not. It is a fat 1/4 wave radiator. In the context of unfolding the radials of a 1/2 wave center fed antenna the idea it is a 3/4 wave because you physically unfold a side of it just doesn't calculate. . .

 

[Needle Bender]

needlebender, I know you're trying to say something here, but it eludes me what it is.
The post quoted makes no sense:


Everyone knows a folded dipole if unfolded will be physically 1/2 wave, but folded back on itself it is not. It is a fat 1/4 wave radiator. In the context of unfolding the radials of a 1/2 wave center fed antenna the idea it is a 3/4 wave because you physically unfold a side of it just doesn't calculate. . .

It is with reference to the folded 3/4 wave AP. You can click on the little arrowhead in front of Freecell's user-name in the quote in my post #103 and read it in context.