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Any Astro Plane Fans ?
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If I move the feed point around the corner, I can't get AGT to line up perfectly. It is reading low. When making adjustments, I was able to get it as close as .978, which should be fine for our needs. This also pushes SWR from the 1.02 range to the 1.2 range range.
If this is the correct place to put the feed point for this antenna I have a question, why is it that the dimensions given by Avanti work perfectly with no modification with the feed point where I had it initially, yet here to get the best match I have to retune the model slightly?
And about the gain difference between the feed point locations...
I should point out that the blue line is slightly under reported as its AGT is slightly lower than the red line.
Sure, I could adjust out the SWR change by modifying the upper vertical element and the cap hat, but with the feed point in the original position everything fell into place without the need for any adjustment anywhere.
This also does nothing to aid in the blue line discussion we had above, it is still their, right were it was to begin with...
Seriously, electrically speaking we are talking a change of almost nothing moving the feed point from one place in question to the other. If you insist that it must be this way, that is fine, and I can live with that. But honestly, I really don't see the point...
The DB
If this is the correct place to put the feed point for this antenna I have a question, why is it that the dimensions given by Avanti work perfectly with no modification with the feed point where I had it initially, yet here to get the best match I have to retune the model slightly?
And about the gain difference between the feed point locations...
I should point out that the blue line is slightly under reported as its AGT is slightly lower than the red line.
Sure, I could adjust out the SWR change by modifying the upper vertical element and the cap hat, but with the feed point in the original position everything fell into place without the need for any adjustment anywhere.
This also does nothing to aid in the blue line discussion we had above, it is still their, right were it was to begin with...
Seriously, electrically speaking we are talking a change of almost nothing moving the feed point from one place in question to the other. If you insist that it must be this way, that is fine, and I can live with that. But honestly, I really don't see the point...
The DB
Ok. I just wanted to see how it affected the blue line. Thanks.
I thought I would have to be a sliggt more provacative in my post to get you, DB, to try the change. It worked and now we know.
I thought I would have to be a sliggt more provacative in my post to get you, DB, to try the change. It worked and now we know.
This is a quote from the old thread I made avout the homebrew PVE and duct tape APv
HomerBB said:
DB, I have found the feed point works at the top of the short side radial and at the base of the shortened radiator with the top hat on the long side with minor tweaking.
I don't think your position is wrong, it is just another location to feed this design. I also used your two short wire idea for the mounting bracket. What dimensions did you use for those two wires...length and diameter? That said however, my effort using your ideas did not produce a good AG resulsts...so I need the secret that ghz24 gave you if you can share it.
In my modeling I try to keep close to specs.,But that is a battle because there are lots of dimensions out there for the A/P that likely work too. Sometimes I get tempted to modify the antenna dimensions rather than work to maybe fix the segments for better results or do something else.
I use a rectangle bracket that is 6" x 2.5" x 0.125" thick in place of the two little wires you use for your mounting bracket. That too, possibly makes some differnece.
The only reason I make the bottom of my rectangle bracket into two short 3" inch wires and you do the same with your design using two short wires for the mounting bracket...is because we will be mounting a mast to this hub and we have to connect the mast wire at a junction of two wires.
The 6" bracket is just one piece on the rectangle side of the Old Top One version. The original A/P uses two similar rectangles that are bolted together securing the radiator at one end and the feed point insulator on the other end.
Here is a link to the patent you requested. Check out in particular column 4 lines 17 - 45 for the part about the bottom being a loop of sorts and how a variety of configurations can produce similar results.
https://www.google.com/patents/US35...ved=0ahUKEwj7gfroqcjUAhUq04MKHYDlBckQ6AEIIjAA
I don't think your position is wrong, it is just another location to feed this design. I also used your two short wire idea for the mounting bracket. What dimensions did you use for those two wires...length and diameter? That said however, my effort using your ideas did not produce a good AG resulsts...so I need the secret that ghz24 gave you if you can share it.
In my modeling I try to keep close to specs.,But that is a battle because there are lots of dimensions out there for the A/P that likely work too. Sometimes I get tempted to modify the antenna dimensions rather than work to maybe fix the segments for better results or do something else.
I use a rectangle bracket that is 6" x 2.5" x 0.125" thick in place of the two little wires you use for your mounting bracket. That too, possibly makes some differnece.
The only reason I make the bottom of my rectangle bracket into two short 3" inch wires and you do the same with your design using two short wires for the mounting bracket...is because we will be mounting a mast to this hub and we have to connect the mast wire at a junction of two wires.
The 6" bracket is just one piece on the rectangle side of the Old Top One version. The original A/P uses two similar rectangles that are bolted together securing the radiator at one end and the feed point insulator on the other end.
Here is a link to the patent you requested. Check out in particular column 4 lines 17 - 45 for the part about the bottom being a loop of sorts and how a variety of configurations can produce similar results.
https://www.google.com/patents/US35...ved=0ahUKEwj7gfroqcjUAhUq04MKHYDlBckQ6AEIIjAA
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Eddie i have not had time to do any astroplane vs the rest A/B tests,
im very happy with how its performing vs locals antennas,
im pretty confident it will at least equal or beat any 5/8 at the same tip height,
NB is wrong about the mast & or coax not been needed inside the aperture of the basket in order to have low vswr with the astroplane as designed by avanti,
NEC is not giving false vswr results,
without the mast the lower half of the antenna is an odd shaped 5/8wave loop with high vswr,
add the mast it becomes a different animal, impedance drops to around 50ohms, mast diamater and spacing effect impedance,
what i would like to know is which of the two versions of where the upper 1/4wave is connected gives the most symetrical pattern,
extending the mast is physically symetrical & looks better but does it give a more or less symatrical pattern ?
im very happy with how its performing vs locals antennas,
im pretty confident it will at least equal or beat any 5/8 at the same tip height,
NB is wrong about the mast & or coax not been needed inside the aperture of the basket in order to have low vswr with the astroplane as designed by avanti,
NEC is not giving false vswr results,
without the mast the lower half of the antenna is an odd shaped 5/8wave loop with high vswr,
add the mast it becomes a different animal, impedance drops to around 50ohms, mast diamater and spacing effect impedance,
what i would like to know is which of the two versions of where the upper 1/4wave is connected gives the most symetrical pattern,
extending the mast is physically symetrical & looks better but does it give a more or less symatrical pattern ?
Am dizzy from reading this thread. Wish I could understand it all. All I know is the Avanti Astro Plane was quieter and pulled in signals better than any ground plane I ever had, including a Shakespeare Big Stick, Radio Shack Archer, and Hy-gain CLR-2 at the same height.
Bob, I did that once and I saw no difference. I thought it might have more to do with the feed point element being off to one side.
I just did it with my idea for DB's A/P model, which is not working like he has shown us. Here is the pattern results for a regular setup and over the mast.
The A/P was the 2nd best antenna I ever owned.
The best was the Astro Beam.
Those were the days.
I don't have one made, but I can make one. I did some more playing, and if the mast is long enough, further down the SWR goes down some more. Over most of the mast length on the original model I used X was capacitive, or negative. Moving the feed point that small amount on the model changes X to be mostly inductive, or positive. I can see this causing what your are describing. Also, I did a quick run of multiple mast lengths, and if their is enough mast their are points where SWR is lower.
This is a dimension that I may need to check now that I am looking at it. They are each just under 7 inches long. Now that I am looking at it, that sounds rather large, I will have to confirm that on the chart. The wire (called "blue line" above) is a half an inch diameter, and the other one varies with the model as I change its diameter to adjust AGT.
As I stated above...
I am using it on a wire that has more than 1 segment, but due to the layout of this antenna, changing the diameter of the wire doesn't change much if anything at all, aside from AGT. I have seen no difference in the patterns created.
Thank you. After I read it perhaps I'll post my thoughts on it...
So you want me to use a feed line and put the source an electrical 1/4 wavelength away from the feed point? I can do that, but I don't see it making any difference... I'll make the model up shortly... After that I will explain why I I think that their is almost no current flowing on that wire.
EDIT**********
The addition of a feed line does not change the current distribution on the antenna itself. It does change the current on the feed point which is now on the other side of the feed line based on how long the feed line is.
The reason that their is almost no current flowing on the "blue line" as we have been calling it is both the mast on one side of it, as well as the upper part of the basket going into the upper vertical element are at current nodes, which means as far as voltage is concerned, both sides of the wire are at or near voltage null's. Current follows voltage, and if their is no voltage available on either side of this wire current simply doesn't flow. The same thing happens on yagi antennas when the center of the individual elements are directly connected to the boom, yet current does not flow on the boom itself (or at least very little).
/EDIT**********
This level of discussion is not everyone's cup of tea. Take from it what you can, and don't be afraid to ask questions, although to might get several different answers...
The DB
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Actually, adding a feed line in like that is throwing everything off...
All currents are listed as 0 uA? I wonder if their is a bug somewhere in the software. Its not just this that is wierd, but the antenna data as well, an SWR of 10.1, and an impedance of 5 - j5? I can go on here, 0% efficiency, yet 153% radiation efficiency? I don't use transmission lines at all really so I am not really sure, and haven't seen them used except when it comes to auto-generated stub matching. It is also possible I could have done something wrong, but I don't know what.
That being said, adding a 1/4 wavelength of in this case 50 ohm feed line between a "source" and where the feed line connects to the antenna, or any amount really, shouldn't make any difference as far as current distribution on the antenna.
Unless you were telling me to connect it differently, at which point I missed what you were saying... Unfortunately I am not certain that I can reliable show you anything using transmission lines at this point.
The DB
All currents are listed as 0 uA? I wonder if their is a bug somewhere in the software. Its not just this that is wierd, but the antenna data as well, an SWR of 10.1, and an impedance of 5 - j5? I can go on here, 0% efficiency, yet 153% radiation efficiency? I don't use transmission lines at all really so I am not really sure, and haven't seen them used except when it comes to auto-generated stub matching. It is also possible I could have done something wrong, but I don't know what.
That being said, adding a 1/4 wavelength of in this case 50 ohm feed line between a "source" and where the feed line connects to the antenna, or any amount really, shouldn't make any difference as far as current distribution on the antenna.
Unless you were telling me to connect it differently, at which point I missed what you were saying... Unfortunately I am not certain that I can reliable show you anything using transmission lines at this point.
The DB