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Post by homerbb on Nov 19, 2010 21:28:06 GMT -5
Made a mobile antenna for the first time. Seems to work well for both local and DX. SWR: 25.615 ------------- 1.5:1 27.205 ------------- <1.1:1 28.305 -------------- 1.2:1 Any thoughts?
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Sandbagger
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Post by Sandbagger on Nov 20, 2010 11:14:14 GMT -5
Made a mobile antenna for the first time. Seems to work well for both local and DX. SWR: 25.615 ------------- 1.5:1 27.205 ------------- <1.1:1 28.305 -------------- 1.2:1 Any thoughts? Looks nice. How tall is it?
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Post by Tombstone (R.I.P.) on Nov 20, 2010 18:41:31 GMT -5
It looks like it's pretty long. That's what I call an antenna. With a standing wave ratio like that I'd bet is works well. Nice job.
Tombstone
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Post by homerbb on Nov 20, 2010 22:01:03 GMT -5
It works very well. I get out extremely good, and it has the ears of an elephant. Yes it's long, too long, so I am still working on it. i have some changes to make to the size of the coil so I can find a match with a shorter antenna.
Thanks!
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Sandbagger
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Post by Sandbagger on Nov 21, 2010 10:33:00 GMT -5
It works very well. I get out extremely good, and it has the ears of an elephant. Yes it's long, too long, so I am still working on it. i have some changes to make to the size of the coil so I can find a match with a shorter antenna. Thanks! I guess the thing that has me scratching my head is, considering how long it is, is there any performance advantage to using that coil over a straight 102" whip?
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Post by jacobs132 on Nov 21, 2010 13:03:52 GMT -5
i was just wondering if the antenna is resonant on 11 meters considering its length on top of the coil?. swr isnt always the answer to how a antenna is working, jim
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Post by homerbb on Nov 21, 2010 14:32:03 GMT -5
Two things I've been led to believe respective of the length of the antenna.
1. Every antenna that has a coil experiences loss from the coil, so I would imagine a straight 102" whip would have some advantage over this one, however, I doubt at this one's length above the coil that advantage would be noticeable.
2. The open air coil type antennas do their radiating from the top of the coil, and the length above the coil - say the whip, for instance - is simply utilized to tune the match to the radio. If that is the case, then my goal is to devise a coil that will maximize the performance as well as I'm experiencing with this one without the need to have the upper matching system so long.
I am inclined to accept this second principle on the basis of the fact that a 102" whip with a 4" - 6" spring, or a 108" whip without the spring is a complete 1/4 antenna using the vehicle as its ground plane, no different than a 1/4 wave GP base antenna using radials to balance the 1/4 wave radial.
Apparently the electrical properties of the coil maintain an electrical similarity to the physical properties of the 1/4 whip without need for the actual length.
Now I've spoken way beyond my education . . .
Still working on it.
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Sandbagger
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Post by Sandbagger on Nov 22, 2010 8:27:49 GMT -5
Two things I've been led to believe respective of the length of the antenna. 1. Every antenna that has a coil experiences loss from the coil, so I would imagine a straight 102" whip would have some advantage over this one, however, I doubt at this one's length above the coil that advantage would be noticeable. 2. The open air coil type antennas do their radiating from the top of the coil, and the length above the coil - say the whip, for instance - is simply utilized to tune the match to the radio. If that is the case, then my goal is to devise a coil that will maximize the performance as well as I'm experiencing with this one without the need to have the upper matching system so long. I am inclined to accept this second principle on the basis of the fact that a 102" whip with a 4" - 6" spring, or a 108" whip without the spring is a complete 1/4 antenna using the vehicle as its ground plane, no different than a 1/4 wave GP base antenna using radials to balance the 1/4 wave radial. Apparently the electrical properties of the coil maintain an electrical similarity to the physical properties of the 1/4 whip without need for the actual length. Now I've spoken way beyond my education . . . Still working on it. Actually, I think you have it a little backward. The portion of the antenna above the coil is what radiates the most signal. The coil is what makes up for the shortened length and, by adding inductance, provides the proper impedence for the physically shortened radiator. You can inductively load practically any length antenna, and make it look like a electrical 1/4 wave. The difference is that the longer the antenna, the more radiation area there is, which generally means that it will work better than a shorter (and also loaded) antenna. That's why a center loaded 60" antenna radiates better than a center loaded 24" antenna. There may be some special circumstances where a particular shortened antenna, has a radiation angle that differs from a longer antenna, which might make it perform better in a particular direction, but generally speaking, the longer the better (up to the full 1/4 wave). The challenge is to shorten an antenna to a practical length, while minimizing the inductive losses, so that overall performance is only slightly less than the full length 1/4 wave antenna. That's why large open air coils are all the rage these days. They generally have less loss than tightly wound coils with greater amount of turns of thin wire.
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Post by cbrown on Nov 22, 2010 9:40:46 GMT -5
Made a mobile antenna for the first time. Seems to work well for both local and DX. SWR: 25.615 ------------- 1.5:1 27.205 ------------- <1.1:1 28.305 -------------- 1.2:1 Any thoughts? Wow, that's pretty broad banded! I'm usually happy if I can get the antenna to have a 2.0 SWR curve with a 2 Mhz bandwith at 11 meters. And you say it really works well, too. Very nice!
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Post by homerbb on Nov 22, 2010 11:43:16 GMT -5
Made a mobile antenna for the first time. Seems to work well for both local and DX. SWR: 25.615 ------------- 1.5:1 27.205 ------------- <1.1:1 28.305 -------------- 1.2:1 Any thoughts? Wow, that's pretty broad banded! I'm usually happy if I can get the antenna to have a 2.0 SWR curve with a 2 Mhz bandwith at 11 meters. And you say it really works well, too. Very nice! Thanks. I was surprised.
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Post by homerbb on Nov 22, 2010 11:45:17 GMT -5
Now I've spoken way beyond my education . . . Actually, I think you have it a little backward. The portion of the antenna above the coil is what radiates the most signal. The coil is what makes up for the shortened length and, by adding inductance, provides the proper impedence for the physically shortened radiator. You can inductively load practically any length antenna, and make it look like a electrical 1/4 wave. The difference is that the longer the antenna, the more radiation area there is, which generally means that it will work better than a shorter (and also loaded) antenna. That's why a center loaded 60" antenna radiates better than a center loaded 24" antenna. There may be some special circumstances where a particular shortened antenna, has a radiation angle that differs from a longer antenna, which might make it perform better in a particular direction, but generally speaking, the longer the better (up to the full 1/4 wave). The challenge is to shorten an antenna to a practical length, while minimizing the inductive losses, so that overall performance is only slightly less than the full length 1/4 wave antenna. That's why large open air coils are all the rage these days. They generally have less loss than tightly wound coils with greater amount of turns of thin wire. I told you so . . . Thanks, Sandbagger. You help me get my foot out of the doo-doo
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Post by homerbb on Nov 22, 2010 19:34:53 GMT -5
Today I rewound a coil of 3 wraps and 5" diameter and 6" top to bottom. The SWR curve is roughly the same as it was, but the antenna is 14" shorter now. The present redone coil is made of 1/4" copper pipe, so is really ugly. I will not keep the pathetic little spindly looking coil. More changes tomorrow. It has gotten dark and supper approaches so I pulled the SUV into the garage for tonight. I don't know if the performance will suffer with the changes until tomorrow. We'll find out.
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Sandbagger
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Post by Sandbagger on Nov 22, 2010 22:10:58 GMT -5
Today I rewound a coil of 3 wraps and 5" diameter and 6" top to bottom. The SWR curve is roughly the same as it was, but the antenna is 14" shorter now. The present redone coil is made of 1/4" copper pipe, so is really ugly. I will not keep the pathetic little spindly looking coil. More changes tomorrow. It has gotten dark and supper approaches so I pulled the SUV into the garage for tonight. I don't know if the performance will suffer with the changes until tomorrow. We'll find out. The new coil most likely has a higher inductance, which allowed you to shorten the antenna rod. Do you have an MFJ Antenna Analyzer? If not, you might want to consider purchasing one. It's an indispensible tool for anyone who seriously tinkers with antennas.
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Post by homerbb on Nov 23, 2010 0:34:08 GMT -5
Today I rewound a coil of 3 wraps and 5" diameter and 6" top to bottom. The SWR curve is roughly the same as it was, but the antenna is 14" shorter now. The present redone coil is made of 1/4" copper pipe, so is really ugly. I will not keep the pathetic little spindly looking coil. More changes tomorrow. It has gotten dark and supper approaches so I pulled the SUV into the garage for tonight. I don't know if the performance will suffer with the changes until tomorrow. We'll find out. The new coil most likely has a higher inductance, which allowed you to shorten the antenna rod. Do you have an MFJ Antenna Analyzer? If not, you might want to consider purchasing one. It's an indispensible tool for anyone who seriously tinkers with antennas. I do not have an analyzer. I hope to get one as soon as possible. I've looked at them but they are not in the budget, yet.
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Post by cbrown on Nov 23, 2010 9:29:46 GMT -5
If you are designing antennas, the MFJ's are a very valuable tool to have.
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Post by homerbb on Nov 23, 2010 14:15:24 GMT -5
If you are designing antennas, the MFJ's are a very valuable tool to have. I know . . . now I'm depressed . . . back to work.
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Post by homerbb on Nov 23, 2010 21:55:27 GMT -5
I will begin to modify the second prototype to nearer its permanent form soon. As a record on the thread here are some photos of the changed antenna from the above model. Larger coil, shorter overall height. The ugly tubing coil will be replaced.
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Sandbagger
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Posts: 6,250
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Post by Sandbagger on Nov 23, 2010 21:55:40 GMT -5
If you are designing antennas, the MFJ's are a very valuable tool to have. I know . . . now I'm depressed . . . back to work. Hey! It's not too late. Santa is coming in a month........ ;D
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Sandbagger
Administrator/The Boss
Posts: 6,250
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Post by Sandbagger on Nov 23, 2010 21:58:24 GMT -5
I will begin to modify the second prototype to nearer its permanent form soon. As a record on the thread here are some photos of the changed antenna from the above model. Larger coil, shorter overall height. The ugly tubing coil will be replaced. The coil might not be the straightest, but the antenna is starting to resemble a Dave Made or other "big coil" antennas. You're not far off now.......
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Post by homerbb on Nov 23, 2010 22:22:29 GMT -5
That spindly little copper coil will get replaced by aluminum flat bar as in the first one. I just didn't want to coil the aluminum with the result being so permanent. The copper was to try it out first. An advantage of the flat bar is it shapes up more perfectly. The trick is getting a good coil, but I have a method . . .
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Post by Tombstone (R.I.P.) on Nov 24, 2010 3:00:42 GMT -5
I think that your antenna will result in a fine performer. Just a comment from here, but over the years and all of the mobile antennas that I've tried, the center loaded ones seem to work the best, although the longer, the better, to a point that they're too long. Still, you won't get a better performer than the old 102 inch whip with a six inch spring that makes it a full 1/4 wave.
Tombstone
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Sandbagger
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Posts: 6,250
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Post by Sandbagger on Nov 24, 2010 8:52:22 GMT -5
I think that your antenna will result in a fine performer. Just a comment from here, but over the years and all of the mobile antennas that I've tried, the center loaded ones seem to work the best, although the longer, the better, to a point that they're too long. Still, you won't get a better performer than the old 102 inch whip with a six inch spring that makes it a full 1/4 wave. Tombstone Yep, and the most ideal setup would be a 1/4 wave whip smack dab in the middle of a large van or SUV roof (Larger ground plane). But an 8' whip in the middle of the roof is not practical for normal city driving. So that's where shortened antennas come in. It then becomes a choice between losing a slight amount of radiation, but still putting the antenna in the best location, or running the best antenna, but being forced to mount it in a less desirable place, like the rear bumper.
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Post by homerbb on Nov 24, 2010 9:34:32 GMT -5
You gents have hit it on the head with my situation. I live in town, and do most of my driving here. The 1/4 whip has always been the antenna of choice for my pickup trucks, but I drive a SUV now and for the foreseeable future. When I get it right this antenna will go on a multiple magnet mount on the roof of the SUV. Already I've put a bottom load antenna in the center of the SUV to see if I heard as well. I took it back off immediately. By comparison the bottom load rat shack was disappointing. I bought it for the SS whip to use in this antenna.
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Post by homerbb on Nov 24, 2010 14:19:38 GMT -5
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Post by homerbb on Nov 24, 2010 14:54:37 GMT -5
Oops! Coil was wrong. I wanted 5" x 6" x 3 turns. Fixed.
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Post by homerbb on Nov 25, 2010 10:54:44 GMT -5
Here is a side-by-side photo of the first antenna and the modified version. This clearly illustrates the height difference the new coil accomplished.
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Post by homerbb on Dec 2, 2010 9:22:30 GMT -5
In the first of these two photos it shows the antenna on a homebrewed triple magnet mount on the roof. At 55 MPH it came unglued from the roof top. I will have to add more magnets for this one. The second photo shows a shot of the antenna sporting two wraps on a shorter center insulator. This change I did during my lunch break last night. However, the antenna seemed to suffer some noticeable performance reduction. I will be putting a longer lower shaft on it to see if I regain performance.
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Post by homerbb on Dec 6, 2010 16:03:57 GMT -5
Latest model. I don't know how it stacks up to the others until I run it a little while.
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Post by cbrown on Dec 7, 2010 9:44:10 GMT -5
Looks pretty sweet, Homer!
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Post by homerbb on Dec 7, 2010 9:57:29 GMT -5
Looks pretty sweet, Homer! Thanks.
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