Repost from Ham antenna forum in case some of you don't look up there.
http://www.worldwidedx.com/amateur-...mhz-bandwidth-10-11m-vertical.html#post390407
http://www.worldwidedx.com/amateur-...mhz-bandwidth-10-11m-vertical.html#post390407
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New 11 Meter Vertical Challenge
- Thread starter Wire Weasel
- Start date
Here's How To Build One
1. Fiberglass pole approx. 15'7" tall, with base 1 3/8" diameter. (The LDG S9v18 is what I used.)
2. Run a piece of stranded, insulated #10 wire inside the tube from top to bottom. Leave about 6" to connect to a 1:1 current balun. (LDG supplies a free one with every purchase. Also, LDG already has a wire inside, so all I did was cut it to length.)
3. Wrap the base with Aluminum foil (or aluminium if you are British) from the bottom up to 43".
4. Connect about 6" of wire from the bottom of the aluminum to connect to the 1:1 balun.
5. Mount the antenna on a piece of wood -- like a broomstick or shovel handle.
6. Connect 50 Ohm coax to the balun.
7. You MAY have to adjust the dimensions a bit to get 6 MHz, but the above should get you close. Also, you MAY have to add a couple of clamp-on ferrites to reduce the Common Mode on the coax.
I have photos in my wwdx photo album, but I don't seem to be able to get them to load here. If someone can help, I'd sure appreciate it!
I've also built a similar unit for 2M. It has a 2:1 VSWR bandwidth from about 120MHz to 170 MHz.
All the best,
Bill
1. Fiberglass pole approx. 15'7" tall, with base 1 3/8" diameter. (The LDG S9v18 is what I used.)
2. Run a piece of stranded, insulated #10 wire inside the tube from top to bottom. Leave about 6" to connect to a 1:1 current balun. (LDG supplies a free one with every purchase. Also, LDG already has a wire inside, so all I did was cut it to length.)
3. Wrap the base with Aluminum foil (or aluminium if you are British) from the bottom up to 43".
4. Connect about 6" of wire from the bottom of the aluminum to connect to the 1:1 balun.
5. Mount the antenna on a piece of wood -- like a broomstick or shovel handle.
6. Connect 50 Ohm coax to the balun.
7. You MAY have to adjust the dimensions a bit to get 6 MHz, but the above should get you close. Also, you MAY have to add a couple of clamp-on ferrites to reduce the Common Mode on the coax.
I have photos in my wwdx photo album, but I don't seem to be able to get them to load here. If someone can help, I'd sure appreciate it!
I've also built a similar unit for 2M. It has a 2:1 VSWR bandwidth from about 120MHz to 170 MHz.
All the best,
Bill
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Article On This Antenna
The December issue of antenneX, the online antenna magazine, has just been published. It features my article describing this antenna in greater detail.
73,
Bill
KT4YE
The December issue of antenneX, the online antenna magazine, has just been published. It features my article describing this antenna in greater detail.
73,
Bill
KT4YE
The thread got off to a bad start...with a food fight, but if this article is in the public domain, which I doubt considering antennaX looks to be charging for everything on their site, give us a link. I'll read it.
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Hi Eddie...
The article is copyrighted, so I can't send a copy. Each month, SOME of the articles are available as "freebies." Most are not. Since I'm a long-time subscriber, they all come free to me!
Another approach might be to contact the publisher, Jack Stone and ask him. The worst that can happen is that he says, "no."
Bill
The article is copyrighted, so I can't send a copy. Each month, SOME of the articles are available as "freebies." Most are not. Since I'm a long-time subscriber, they all come free to me!
Another approach might be to contact the publisher, Jack Stone and ask him. The worst that can happen is that he says, "no."
Bill
It should be fairly simple to analyze the antenna, determine how it's constructed. Is it a simple fraction of a wave length (1/4, 1/2, 5/8, etc.), or an array of any of those? Does it use an impedance matching scheme/device of some sort?
Then it should be a fairly simple scaling for a different frequency.
Once you are at that point try plugging the numbers into that antenna modeling program. It won't come out exactly by any means, but it would get you into the ball-park where you can optimize for things.
I don't see any copy write or patent infringements in that, it's a very typical/normal practice.
- 'Doc
Then it should be a fairly simple scaling for a different frequency.
Once you are at that point try plugging the numbers into that antenna modeling program. It won't come out exactly by any means, but it would get you into the ball-park where you can optimize for things.
I don't see any copy write or patent infringements in that, it's a very typical/normal practice.
- 'Doc
Hello Doc...
The antenna is easily modeled in EZNEC. When I built the first one, I had to make just a small (~3%) adjustment in the overall length vs. the modeled length to get it to resonate. That was almost certainly due to a variation in wire size vs. the model.
The major difference was in the bandwidth. EZNEC said it should have about 1.8 MHz 2:1 bandwidth for 10M. It actually covers MUCH more than that.
There are no impedance matching devices. IOW no gamma match. No inductors. No capacitors. No transformers. Just PVC and metal.
The coax shield goes to the Metal cylidrical outer conductor. The coax center conductor goes to the monopole that runs from the base, through the cylinder and upwards.
The total heigth of the antenna is just under 1/2 wavelength -- call it 3/8 wave or thereabouts. The metal sheath is roughly 1/8 wavelength.
The antenna is a bit unbalanced, so I strongly suggest that either a 1:1 current balun be used (or several ferrite beads) to keep any common mode currents from making their way back to the shack.
As I mentioned earlier, I have pictures , but I haven't figured out how to post them! :-(
Let me try this... here's a picture of the antenna on the back deck. The box at the end of the cable is my MFJ. It is battery operated and the only connection is to the antenna. http://www.worldwidedx.com/members/kt4ye-albums-searchlight-picture3541-searchlight-sept-30-001.html
This is the MFJ reading at resonance: http://www.worldwidedx.com/members/kt4ye-albums-searchlight-picture3571-searchlight-sept-16-005.jpg
This is the MFJ reading at the lowest frequency: http://www.worldwidedx.com/members/kt4ye-albums-searchlight-picture3573-searchlight-sept-16-003.jpg
This is the MFJ reading at the highest frequency: http://www.worldwidedx.com/members/kt4ye-albums-searchlight-picture3574-searchlight-sept-16-004.jpg
Bill
Just 'playing' with some numbers you furnished...
A 1/2 wave of wire sticking out of a 1/8th wave of tubing. Does that remind you of something? How about a Zepp, or a 'J'-pole? Not the 'classic' lengths, but close, sort of.
(And no matter what that SWR meter says, the 'X' below it tells the story when using a '259'.)
Something else you might consider. What determines the impedance of coax cable? It's the diameters of the center conductor and the shield (outer tubing) and the electrical characteristics of the insulation between the two, right? That impedance (Z) is always composed of (R +/- J) and varying the dimensions of the cable changes that 'R' and 'J' (or 'X' if you're using a '259).
Doesn't that make the 'tubing' an impedance matching device? Not a very 'handy', or convenient way of doing it, but certainly possible.
- 'Doc
A 1/2 wave of wire sticking out of a 1/8th wave of tubing. Does that remind you of something? How about a Zepp, or a 'J'-pole? Not the 'classic' lengths, but close, sort of.
(And no matter what that SWR meter says, the 'X' below it tells the story when using a '259'.)
Something else you might consider. What determines the impedance of coax cable? It's the diameters of the center conductor and the shield (outer tubing) and the electrical characteristics of the insulation between the two, right? That impedance (Z) is always composed of (R +/- J) and varying the dimensions of the cable changes that 'R' and 'J' (or 'X' if you're using a '259).
Doesn't that make the 'tubing' an impedance matching device? Not a very 'handy', or convenient way of doing it, but certainly possible.
- 'Doc
Hi Doc....
You are on the right track with your thinking WRT the metal cylinder. It is a short section of coaxial transmission line with a Zo of around 160 Ohms.
Using EZNEC, I've modeled this device as an assymetrical sleeve dipole (source at the center) AND as an end fed device. The elevation patterns are essentially the same. The modeled bandwidths are also the same -- ~ 5%.
But my *measured* bandwidth is WAY bigger.
With a sleeve dipole, the bottom of the metal cylinder is "hot" with RF. (It's at the High impedance end of a dipole secton.) And that implies *large* amounts of Common Mode current induced onto the feedline coax shield.
With my design, the impedance where the coax shield attaches to the bottom is at a relatively low impedance location. There is *some* CM, but not a lot.
The biggest "mystery" for me is the unexpectedly wide bandwidth. I'm convinced the Cylindrical element is acting as some kind of a matching section, but I haven't yet figured out how it works!
Anyone with ideas, PLEASE "jump in."
Bill
You are on the right track with your thinking WRT the metal cylinder. It is a short section of coaxial transmission line with a Zo of around 160 Ohms.
Using EZNEC, I've modeled this device as an assymetrical sleeve dipole (source at the center) AND as an end fed device. The elevation patterns are essentially the same. The modeled bandwidths are also the same -- ~ 5%.
But my *measured* bandwidth is WAY bigger.
With a sleeve dipole, the bottom of the metal cylinder is "hot" with RF. (It's at the High impedance end of a dipole secton.) And that implies *large* amounts of Common Mode current induced onto the feedline coax shield.
With my design, the impedance where the coax shield attaches to the bottom is at a relatively low impedance location. There is *some* CM, but not a lot.
The biggest "mystery" for me is the unexpectedly wide bandwidth. I'm convinced the Cylindrical element is acting as some kind of a matching section, but I haven't yet figured out how it works!
Anyone with ideas, PLEASE "jump in."
Bill
Hi all !
Eh.. like a open sleeve antenna ?
Alwasy fascinating to see people willing to investigate the deeper "why".
Just to be on the positive critical side..
Im aware you already asked roy if he could think of a way to model a EH antenna.
But have you also verified if he thinks your present model is accurate ?
Beeing a fanatic "modeler" your self, you are aware that there are limitations.
What worrie me a bit is that i interpertate the eznec results as proof (gain/take off angle etc) I do think it was intended that way.
But on the other hand eznec told you a different story regarding the SWR.
So for me, that makes the first part rather unstable.
And yes we all know: it is possible to work brazil with a mobiel antenna. Infact i worked New Zealand (otherside of the globe for me) via L.P on a wilson last week..so, that doesnt count.
With that said...Im not saying the antenna doesnt do what the provided plots tells us.
Except for the bandwidth (which so far, i dont understand either)
All the figures are a sure "can be".
Ah thats another thing..normally extra large SWR bandwidth isnt a really good thing, as you know..
So it would be great if we have a "additional" antenna along with the other "wide band" options !
To bad it is so bussy...perhaps with the christmas days i migth be able to measure the gain or try to find out what
nec4 (closed spaced wires) or CST says about it.
anyway...I am thinking of constructing one..so ill keep a eye on the thread.
Kind regards,
Keep up the good work guys..
H.
Eh.. like a open sleeve antenna ?
Alwasy fascinating to see people willing to investigate the deeper "why".
Just to be on the positive critical side..
Im aware you already asked roy if he could think of a way to model a EH antenna.
But have you also verified if he thinks your present model is accurate ?
Beeing a fanatic "modeler" your self, you are aware that there are limitations.
What worrie me a bit is that i interpertate the eznec results as proof (gain/take off angle etc) I do think it was intended that way.
But on the other hand eznec told you a different story regarding the SWR.
So for me, that makes the first part rather unstable.
And yes we all know: it is possible to work brazil with a mobiel antenna. Infact i worked New Zealand (otherside of the globe for me) via L.P on a wilson last week..so, that doesnt count.
With that said...Im not saying the antenna doesnt do what the provided plots tells us.
Except for the bandwidth (which so far, i dont understand either)
All the figures are a sure "can be".
Ah thats another thing..normally extra large SWR bandwidth isnt a really good thing, as you know..
So it would be great if we have a "additional" antenna along with the other "wide band" options !
To bad it is so bussy...perhaps with the christmas days i migth be able to measure the gain or try to find out what
nec4 (closed spaced wires) or CST says about it.
anyway...I am thinking of constructing one..so ill keep a eye on the thread.
Kind regards,
Keep up the good work guys..
H.
After I finished my design, I came across a very thoughtful design for an open sleeve antenna. It was designed to solve the assymetrical pattern problems of a J pole. As such, it's roughly 1/2 wave plus 1/4 wave high. That's MUCH taller than my design. And the paper on that subject: http://k6mhe.com/files/ssfm.pdf did not mention any changes in bandwidth.
Looks like you had a "peek" at my antenneX article, and thanks. But I did not make myself clear -- apparently . I asked Roy if he could come up with a work-around for placing a capacitor in a small loop in order to build a "micro EH" usling a simple L/C network instead of the complex cylinders and coils of the "star" EH. He could not, so I came up with my own solution using a different modeling method.
I'm NEVER gonna claim that I'm a "fantastic" modeler, but (almost) every antenna that I have modeled and built in EZNEC has performed well within experimental limits when I built it. There are two exceptions. This design and the Sigma 4 wherein the radiation pattern depends on where the source is placed.
Roy is generally too busy to look at specific designs, but if I can't get a good explanation for the extended bandwidth, I'll see if I can get him interested.
BUT the fact that the patterns of an assymetrical dipole and my design are identical leads me to believe that the design is OK.
And that leaves the extended bandwidth issue still a "mystery."
YES! Usually, if an antenna is wideband, it's because there are construction issues like bad solder joints, corroded or lossy materials, lossy coils etc.
My design has none of the above. I've built several different versions for 10/11M using different bits and pieces. So has a buddy in the UK.
I've also built a scaled-up version for 2M with similar "excess bandwidth" results.
If/when you give it a try, I'll be happy to help in any practical way!
Bill