Difference in AstroPlane vs. New Top One per Eznec5

[Marconi]

1/4 down, 1/4 up
kinda simple, no?

Well Homer, that's the way it looks to me.

I think I have in mind another "new" way for how the A/P might be working, with all those different currents flowing and about in the bottom.

I see it with some currents in-phase and contributing, and some out-of-phase and canceling. If I'm right then it might help explain how it produces such a big fat wave front of current with lots of current flowing in virtually all of the entire 12' feet of the AstroPlane's physical length.

So, I have a new project.

 

[HomerBB]

Booty, that has been my understanding, but it could be wrong. We shall see.

 

[BOOTY MONSTER]

i checked the PDF and on page 12 it says it needs a minimum of 12 ft of metallic mast .

http://www.cbtricks.com/ant_manuals/avanti/av101/graphics/astro_plane_av101_om.pdf

 

[Marconi]

doesn't the astroplane need a certain minimum length of mast to tune/work properly ? If i recall correctly and it does , shouldn't that be included in the overall length that makes it usable ? i may be remembering wrong though , so someone correct me if i am please .

The mast is truely an important part of my new idea about how the A/P works BM, besides just holding the antenna up and erect.

After Bob started talking about transmission like mode currents and antenna mode currents, I no longer thought my idea for how the A/P works was complete or accurate. I've changed my mind, but this time I think I have proof. If the smilie for "I've got proof" was working, it would surely go here.

Now, due to some modeling experience, I think I understand enough to say and maybe demonstrate in some details, a little better evidence for how it might work. But, if I'm wrong, hopefully we'll have Bob and others that can flesh out the error of my ways.

I'm being a little coy here, but I don't want to prematurely give away my whole idea, but you're right to a point. IMHO, it's not exactly what you might be thinking, but not to worry you're not wrong either.

I've read the patent, and the manual, and I understand the information about making the mast a minimum length below the hoop as you noted. But, I hope to put a real reason to why that may be important...rather than just state a warning.

I wondered about Avanti's warning, and why it was seemingly so important to write about it in the manual. Some may think it has to do with meeting the height issues that surround the legends for the AstroPlane, but NOT ME.

Lastly I wonder about what I see as a function in the bottom of the AP that is similar to another antenna we've discuss...besides when we discussed the Sigma4, and Bob brought the subject up for a while. You remember the stuff about phasing?

Well I could go on, but I'll end up spilling the beans...if I haven't already, and I know this is likely with Bob for sure.

 

[Marconi]

i checked the PDF and on page 12 it says it needs a minimum of 12 ft of metallic mast .

http://www.cbtricks.com/ant_manuals/avanti/av101/graphics/astro_plane_av101_om.pdf

BM, IMO that is because they warn us to set the A/P at least 4' feet above any other object. If we really think about it, that warning alone should stimulate a lot of questions.

 

[BOOTY MONSTER]

i was wondering if it needed the length for the antenna to work on 27 MHz . if so... 12 + 4 + top-hat puts it over 18 ft .
so you're suspecting the outside of the lower half radiates in phase with the top part ? if it does it isn't symmetrical , but that isn't typically much of a problem with most CB antennas FWICT . and FWICT symmetry is important on the vector/sigma4/lw150 .

 

[Marconi]

i was wondering if it needed the length for the antenna to work on 27 MHz . if so... 12 + 4 + top-hat puts it over 18 ft .
so you're suspecting the outside of the lower half radiates in phase with the top part ? if it does it isn't symmetrical , but that isn't typically much of a problem with most CB antennas FWICT . and FWICT symmetry is important on the vector/sigma4/lw150 .

OK, hang on BM. Here is my idea on the 4' foot warning at the bottom below the hoop. I promised not to do my idea this way, because I wanted to check the modeling part out first, but before you get ahead of me, here is my opinion.

The 4' warning is so other stuff below the antenna will be at least far enough away from the hoop as to not interfere with its work. Besides the hoop connecting the two sides of this antenna, I see its actual work, due to current cancellation that is due to the high impedance condition in the hoop. This setup is trying to decouple the RF at the bottom of the 8' foot part of the mast...inside the down radials, just like we would hope to do using a coax choke.

If you look at the images below, both at 48' feet, you will see what I'm trying to describe is pretty much what is happening. The currents are obviously not completely decoupled at the hoop, but the lack of currents on the mast below the hoop are much better than the same antenna with no hoop at all.



So, in answer to your question, NO!

Due to to an out of phase condition (transmission-line mode currents) between the two radials, the current flowing there is canceled. The 8' foot mast inside the radials and the top element, with the top hat, are in phase with nearly the same magnitude of current...and they are in combination...radiating as a 1/2 wave radiator with heavier than normal antenna mode currents. The reason the currents are heavier than normal is because the voltage nodes occur mostly on the top hat and the hoop at the bottom and therefore there is more than a normal amount of current flowing across this 12 feet for the radiator's current distribution. This appears to be some magic that the guys at Avanti used quite often.

Do we see here some of the same type of magic going on in a similar condition with another antenna we talk about? The first one to answer this correctly...gets a big wave from me.

I'll be working on a model view showing the currents and their phase, that hopefully demonstrates this happening in the bottom of the AstroPlane.

 

[HomerBB]

You alude to the GM . . . ?

 

[Marconi]

You alude to the GM . . . ?

Your right young man, you get a big ole' wave.

I'm working on more about this A/P.

If the winds here would slow down a bit, I would try and modify my A/P to an idea I think Bob suggested. I'll be doing that maybe tomorrow, if I don't pass out. I would love to test it out in the real world.

It doesn't look to do much for the gain or angle of the primary lobe, but the pattern's secondary lobe comes up closer to the max gain and covers from 8 to 25 degrees much better, maybe by 1-3 dbi.

I took a long nap yesterday after that DXcapade and I couldn't get back to sleep.

 

[HomerBB]

I woke up and couldn't go back to sleep. Getting old I guess.
I may need to move the choke down lower than 9' below the loop . . . or disregard its use altogether.

 

[HomerBB]

Marconi,
Although it is slightly off topic at this point in the thread I want to refer back to a question youaskedme before about the AP; whether moving the crossbar up or down thereby changing the spread of the two downward radial legs changed centr frequency or not. My reply remains the same as then. I did not pay attention to anything but the SWR, and it definitely moved that. On the acceptable assumption that SWR shifts coincide with some resonance shift I would conclude that is does. What I can not recall is which way I moved it resulted in which change.

 

[gamegetter]

greetings guys;

i playing catch up as i could not get back on last night...

it appears to me that "physically" the AP top is a 1/8 wave, but electrically it is a 1/4 wave with the top hat and the hat does not need to measure out physically to exhibit the 1/4 wave, i'm sure you are aware of that. And so you just have to explain it as such.

Now with the 12' mast info you provided BM and thanks, which i had not had time to look up the distance exactly (which is why i referenced the 20' max height restriction of when it was designed for)...12'+9'(electrical)=21' very close to the 5/8 wave they describe on the original box and it would fit nicely for those folks observing the max legal limit at the time!

 

[Marconi]

Marconi,
Although it is slightly off topic at this point in the thread I want to refer back to a question youaskedme before about the AP; whether moving the crossbar up or down thereby changing the spread of the two downward radial legs changed centr frequency or not. My reply remains the same as then. I did not pay attention to anything but the SWR, and it definitely moved that. On the acceptable assumption that SWR shifts coincide with some resonance shift I would conclude that is does. What I can not recall is which way I moved it resulted in which change.

Homer, I agree that should, would, or could change the match for two reasons.

1. I think the down radial under the feed point is a 1/4 wave stub that is feeding the antenna, working against the mast as a ground. This match is similar to the old Zeppelin and the feeder used on the Signal Engineering's voltage fed Quad design. I'll post a picture of it, if you would like some close up detail to dual polarity feed your quad.

2. This idea is also noted and well detailed in the A/P's patent to change the feed point match.

What I probably meant to say earlier in this regard, was that the model did not appear to respond to that type of adjustment when I first tried it. I'll have to recheck all the dimensions and angles like I did the other day with my I-10K. The only reason I didn't per sue this adjustment idea further is because changing this particular model in that area involves changes to at least two of the radial wires and all of the wires for the loop...and that gets complicated trying to do it manually, and keeping all the wires connected like they should be.

Right now this model is showing an SWR match of 1.339 at the feed point, but the source is not precisely at the same point as it is on the A/P. It is close though, and I think the length of those radials would surely change the source location.

 

[gamegetter]

OK, hang on BM. Here is my idea on the 4' foot warning at the bottom below the hoop. I promised not to do my idea this way, because I wanted to check the modeling part out first, but before you get ahead of me, here is my opinion.

The 4' warning is so other stuff below the antenna will be at least far enough away from the hoop as to not interfere with its work. Besides the hoop connecting the two sides of this antenna, I see its actual work, due to current cancellation that is due to the high impedance condition in the hoop. This setup is trying to decouple the RF at the bottom of the 8' foot part of the mast...inside the down radials, just like we would hope to do using a coax choke.

If you look at the images below, both at 48' feet, you will see what I'm trying to describe is pretty much what is happening. The currents are obviously not completely decoupled at the hoop, but the lack of currents on the mast below the hoop are much better than the same antenna with no hoop at all.

View attachment 7114 View attachment 7116

So, in answer to your question, NO!

Due to to an out of phase condition (transmission-line mode currents) between the two radials, the current flowing there is canceled. The 8' foot mast inside the radials and the top element, with the top hat, are in phase with nearly the same magnitude of current...and they are in combination...radiating as a 1/2 wave radiator with heavier than normal antenna mode currents. The reason the currents are heavier than normal is because the voltage nodes occur mostly on the top hat and the hoop at the bottom and therefore there is more than a normal amount of current flowing across this 12 feet for the radiator's current distribution. This appears to be some magic that the guys at Avanti used quite often.

Do we see here some of the same type of magic going on in a similar condition with another antenna we talk about? The first one to answer this correctly...gets a big wave from me.

I'll be working on a model view showing the currents and their phase, that hopefully demonstrates this happening in the bottom of the AstroPlane.

Would you not want to model at 12', can you explain other wise the 48 foot?

 

[Marconi]

Would you not want to model at 12', can you explain other wise the 48 foot?

Maybe so GG. I just used a random model I had on file. Is there something particular you have in mind about it being 12' feet?

It happened be set at 48' feet high to the hub, so the mast is 48' feet long. My model was done at this height, because that is the highest I can go with my Top One, and I wanted to see what Eznec suggested it might look like up that high.

Wire #45, is shown at the bottom of the Antenna View for my model, "Astro Plane - Top One Fixed 3."