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ASTROPLANE best vertical antenna ever?
- Thread starter nosepc
- Start date
FC, I actually started with the Antenna Mast ending at 48" inches below the radial loop.
This 48" was suggested as a minimum spacing from the loop to the mast or tower in the Manual. I found that when set at 48" inches the resistance for the match was < l0 ohms, and >10 ohms for the reactance.
I also found I could only see a workable match of about 34.72 +J 1.971 ohms = 1.445 SWR...when I had the Antenna Mast terminated at least 65" inches or more below the radial loop. In this configuration the Antenna Mast length was approximately 152" inches long overall. This length produced gain and angle of 2.02 dbi at 13* degrees above the horizon.
As I made the Antenna Mast longer the match and gain improved, but the maximum gain angle for this Free Space model also increased steadily up to 21* degrees above the horizon when I stopped. I never did see the high angle maximum gain points that DB noticed when he did his original testing of this idea. With using 12" inch comparison measurements...I could have skipped right over the results he noted.
This 48" was suggested as a minimum spacing from the loop to the mast or tower in the Manual. I found that when set at 48" inches the resistance for the match was < l0 ohms, and >10 ohms for the reactance.
I also found I could only see a workable match of about 34.72 +J 1.971 ohms = 1.445 SWR...when I had the Antenna Mast terminated at least 65" inches or more below the radial loop. In this configuration the Antenna Mast length was approximately 152" inches long overall. This length produced gain and angle of 2.02 dbi at 13* degrees above the horizon.
As I made the Antenna Mast longer the match and gain improved, but the maximum gain angle for this Free Space model also increased steadily up to 21* degrees above the horizon when I stopped. I never did see the high angle maximum gain points that DB noticed when he did his original testing of this idea. With using 12" inch comparison measurements...I could have skipped right over the results he noted.
Marconi,
simulating a load using R 34.7 + jX 2.0 ohms and having no idea as to the length of line between your antenna and measuring device, modeling the load with my own program using a halfwave line @ 27.185 mhz., i'm looking @ a transline input R of 35 ohms and jX equal to 2 ohms of capacitive reactance with 1.43:1 swr at the transmitter and 1.44:1 swr at the antenna. feedline is lmr400 with a length of 15.3772 feet and line loss due to attenuation is 0.099 dB., ninety nine thousanths of 1 deciBel. there is an additional 0.007 dB. of loss created by the reflection and minimal standing waves on the line resulting in a total system loss of 0.106 dB..
no where near the 4% of reflected power believed by most to be incurred @ an swr of 1.5:1. by comparison as you can clearly see, for an swr of 1.5:1 to be responsible for a 4% loss in power due to reflection from the load you would think that one would have to be using some pretty lossy line. where swr is concerned however, it is reduced as the line loss increases with length while actual power loss continues to increase, transline input impedance is raised or lowered and reactance is reduced. this is the same effect that has been observed by some who are so wrapped up in achieving a perfect match that they choose to operate excessively long and lossy lines, not understanding that as the line becomes longer and loss increases, all load parameters converge towards the characteristic impedance of the line. the end result of this mania is that very little of the source transmitter power makes it to the load to be radiated. but hey, the swr is flat! lol.
..
your mast section, i.e., element 14 is a resonant 1/2 wavelength @ approximately 38.8 mhz., which would, at the very least, explain the low value of R and the attendant swr @ the preferred operating frequency.
simulating a load using R 34.7 + jX 2.0 ohms and having no idea as to the length of line between your antenna and measuring device, modeling the load with my own program using a halfwave line @ 27.185 mhz., i'm looking @ a transline input R of 35 ohms and jX equal to 2 ohms of capacitive reactance with 1.43:1 swr at the transmitter and 1.44:1 swr at the antenna. feedline is lmr400 with a length of 15.3772 feet and line loss due to attenuation is 0.099 dB., ninety nine thousanths of 1 deciBel. there is an additional 0.007 dB. of loss created by the reflection and minimal standing waves on the line resulting in a total system loss of 0.106 dB..
no where near the 4% of reflected power believed by most to be incurred @ an swr of 1.5:1. by comparison as you can clearly see, for an swr of 1.5:1 to be responsible for a 4% loss in power due to reflection from the load you would think that one would have to be using some pretty lossy line. where swr is concerned however, it is reduced as the line loss increases with length while actual power loss continues to increase, transline input impedance is raised or lowered and reactance is reduced. this is the same effect that has been observed by some who are so wrapped up in achieving a perfect match that they choose to operate excessively long and lossy lines, not understanding that as the line becomes longer and loss increases, all load parameters converge towards the characteristic impedance of the line. the end result of this mania is that very little of the source transmitter power makes it to the load to be radiated. but hey, the swr is flat! lol.
..
your mast section, i.e., element 14 is a resonant 1/2 wavelength @ approximately 38.8 mhz., which would, at the very least, explain the low value of R and the attendant swr @ the preferred operating frequency.
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nfsus while you're at it, why don't you tell us what you did to your A/P to get a better tune?
I I modified the capacity hat because resonance was way to low, below channel one, now resonance is close to channel 20.
Aluminum shorter radials
Diam. of radials= 0.165” = 1/8” = 4.20mm
Length = 20 3/4” . 21” to center of eyelet.
With a bandwidth around 2.100 MHz. I thought it was narrower. That’s why I am asking.
Ok to start with, I suppose I should explain my materials. I use a aluminum sheathed 3/8 coax that was abandoned by a cable television company. It has an aluminum sheath over a foam insulator with a copper center. I've hot access to miles of it. The copper does not seem to affect it and it is very easy to form. This is what is used for the skirt case well as both elements below the support. The upper element is a 3/8 aluminum tubing that is longer than needed so it can be extended of retracted to make a match. There is no top hat. Tried it didnt seem to do much.
The mast is a 20ft stick of 1.5" galvanized tubing mounted to a post driven in the ground. It always returns to the same spot after a tune attempt.
The tuning is accomplished by keeping 12" spacing between the two elements below the support and raising or lowering the spreader pvc rod. The bow angle will change shape of course but 12" spacing does seem to be the ticket. This is where we adjust the swr readings primarily. The overall length of the upper stinger will affect it as well. It become a balancing act of adjusting both the spreader location and the stinger length to dial it in. It's a strange dance honestly. I've not seen much change in the arena of impedance except as the frequency changes but I've not changed my feed point so that's expected.
The vna has helped quite a bit although I have questions still. One question is how I can have an almost perfect match with the skirt 13ft off the ground and at 30ft have swr climb slightly and the phase increase.
The mast is a 20ft stick of 1.5" galvanized tubing mounted to a post driven in the ground. It always returns to the same spot after a tune attempt.
The tuning is accomplished by keeping 12" spacing between the two elements below the support and raising or lowering the spreader pvc rod. The bow angle will change shape of course but 12" spacing does seem to be the ticket. This is where we adjust the swr readings primarily. The overall length of the upper stinger will affect it as well. It become a balancing act of adjusting both the spreader location and the stinger length to dial it in. It's a strange dance honestly. I've not seen much change in the arena of impedance except as the frequency changes but I've not changed my feed point so that's expected.
The vna has helped quite a bit although I have questions still. One question is how I can have an almost perfect match with the skirt 13ft off the ground and at 30ft have swr climb slightly and the phase increase.
This is a shot from a new style or clone. I believe it was not an atvanti but anyway, after we put it up I used the vna to see how it turned out. It is 100% non adjustable. It was mounted on 30ft of 1" galvanized rigid conduit.
Sorry the shot was not too good
Sorry the shot was not too good
nfsus, I tried to adjust the legs that hold the loop with no success. What I did was to replace the stainless steel capacity hat with shorter aluminum ones.
Mine was resonant around 26,855 and by shortening the capacity hat with shorter one did the trick. It makes the antenna shorter, therefore, resonant frequency goes up.
Mine was resonant around 26,855 and by shortening the capacity hat with shorter one did the trick. It makes the antenna shorter, therefore, resonant frequency goes up.