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Base Have a look at this Antenna
- Thread starter AudioShockwav
- Start date
Try increasing the spacing Eddie,
if the characteristic impedance of a tapered transmission-line is determined by the mean spacing of the line & tube diameters, im not sure it is but i think so,
you would need to increase spacing for parallel lines.
if the characteristic impedance of a tapered transmission-line is determined by the mean spacing of the line & tube diameters, im not sure it is but i think so,
you would need to increase spacing for parallel lines.
Well Bob, the patent does say parallel lines, but it also says this point controls the match among other things. The Eznec match was a problem with low impedance when I set the radials parallel, so I tried changing the radial spacing at the mid-point to 13" inches instead of 6"...and WA-LA the match was 1.137:1 SWR'. I changed nothing else and this is where I told Homer I was going to stop for a while. Your comments make me curious so I will continue.
For me, this is just guess-work trying to find a setup that produces the effects of steering as noted in Free Space.
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Eddie,
I doubt you are guessing as much you may think,
avanti can't change the physics of how transmission-lines work,
length, tube diameters, spacing & dielectric,
since they make no mention of loading the lines with a dielectric we can assume its air spaced,
nor do they talk about using different diameter tubes or mast,
they don't talk about using a coax transformer like the astrobeam,
all you have left to achieve what they are claiming is spacing,
avanti can't change what length & spacing of the 1/2" tubes will give a good match to your 50ohm coax.
I doubt you are guessing as much you may think,
avanti can't change the physics of how transmission-lines work,
length, tube diameters, spacing & dielectric,
since they make no mention of loading the lines with a dielectric we can assume its air spaced,
nor do they talk about using different diameter tubes or mast,
they don't talk about using a coax transformer like the astrobeam,
all you have left to achieve what they are claiming is spacing,
avanti can't change what length & spacing of the 1/2" tubes will give a good match to your 50ohm coax.
Nor would I, but who knows. RF steering is not an unknown phenomenon with antennas in the real world...
Homer, are you saying "...maybe try the two radials 18" apart from top to bottom, instead of (edit), the mean of 6" top spacing and 30" bottom spacing." ?
If not, maybe a simple sketch of this idea would help me from getting farther into the weeds.
Homer, what would be a good link to check this out? Maybe it will give me some better clues than just guessing.
I was wondering what the A/P antenna looked like that Avanti described in the patent at column 3 lines 67 thru 75. I remembered some body posting the image below, and maybe this is another idea I should try. This was done by PD0G. He was a new member and he showed us images and photos of his ideas and work. He even did a 70cm set of stacked collinear A/P. Maybe he knew a lot more about the ideas for steering, but now he is gone gone.Too bad!
Link to his 1st post is in the thread below this image:
Click here!
ASTROPLANE best vertical antenna ever?
In this link you will see several links at the bottom of his first post. Check out PD0G on QRZ.com.
Link to his 1st post is in the thread below this image:
Click here!
ASTROPLANE best vertical antenna ever?
In this link you will see several links at the bottom of his first post. Check out PD0G on QRZ.com.
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Looks like PD0G is taking the issue of CMC isolation seriously... nice touch with the groundplane.
Homer I made the top bracket = 15" inch radius. That way I wouldn't have to make a new loop which is currently 30" diameter. This made the antenna longer and I didn't want to mess with trying to re-figure the top and bottom elements.
I ran the match and the value for the impedance went up over 100 ohms. I moved the center of the radials IN toward the mast...and it improved the match a little...but that was defeating the purpose of the idea to keep the radials parallel.
Don't be to mad Homer...when you said PD0G was on to something with radials on his 2 meter A/P...my model shows they work great.
I just today read something that DB said to PD0G back then in the thread I posted and they were talking...that he got some similar results when he applied the idea of radials in his A/P model. I don't have a feed line for the model, so you will still need a choke...so maybe radials are not necessary.
So cheer up, it's great to learn something new.
Edit: I don't have a feed line on my model and the radials have very little current flowing, This was a false alarm. Sorry!
If I didn't fuss-up to this mistake...Bob would be mad too.
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