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Message |
    
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1236
Registered: 9-2004
| | Posted on Monday, February 27, 2006 - 11:51 pm: | 
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would there be any advantage to using 1/4 wavelength radials instead of the 5' 10" ones that come with it?
any disadvantages?
thanks for the help,
matt |
Marconi
Advanced Member
Username: Marconi
Post Number: 614
Registered: 11-2001
| | Posted on Tuesday, February 28, 2006 - 7:50 am: |
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Well Kid I cannot answer positively, but in my testing with a 1/4 wave element the GPK length is absoutely critical. However we all understand that the GP element for a 5/8's wave are not nearly as critical as it is for a 1/4 wave, so who knows? If you test your idea by putting 1/4 wave whips up there on and Imax and you see a big difference let us know.
Only difference that I have ever seen in testing was on an A99, with and without the GP kit. There was a decided differnence in the band width curve between the two. Without GP there is no curve, thus I claim additional ground losses were present in the antenna because the max current was not getting to the radiator where it belongs thus making the antenna match look the way it did. With the GPK there is a nice bandwidth curve presented as one would expect from a GP antenna, thus I believe the antenna was improved substaintely. However this difference is typically unnoticable in real world practice, because gain in an antenna at the high end of the gain scale has a very dubious affect in radio work. Classic example is the amout of power it takes to really make a difference using an amplifier. Now if I could ever find a station out there that was at the very end of my radiated field pattern that I could identify, then working that station might show some difference between having a GPK and not. |
Hotwire
Advanced Member
Username: Hotwire
Post Number: 980
Registered: 1-2005
| | Posted on Tuesday, February 28, 2006 - 8:59 am: |
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You would think that the radials that came with the kit would be the best. If 1\4 wavelength radials was better would'nt they just build them like that? Who knows? Maybe your on to something. |
Tech833
Moderator
Username: Tech833
Post Number: 1233
Registered: 8-2002
| | Posted on Tuesday, February 28, 2006 - 10:55 am: |
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full 1/4 length radials will help a little, but not much. I doubt you would ever notice it in any measureable way. |
Marconi
Advanced Member
Username: Marconi
Post Number: 615
Registered: 11-2001
| | Posted on Tuesday, February 28, 2006 - 10:56 am: |
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Hotwire, I believe you have it pretty good.
They just don't need as much, and seeing as it is difficult to tell any real difference, how can we prove anything except by observations or testing. It you can not hear or see it don't mean there is no differences. So, if you can test it and see a difference, then you know there is a difference without seeing or hearing. That is called association by common sense with a little faith.
Now does that convince you Kid? Nope if you just determine everything there is about your radio system based on using your S-meter to tell you how good things are. Then I hear so much from them same peckerwoods that claim how bad them meters really are and that you can't trust your S-meter. No wonder there is confusion in the CB world.
Just do a simple bandwidth test on your antenna and if it shows a flat match from 25.000 to 29.000 then you are likely using ground losses to the max to improve the match only and all to the expense of some possible gain that the antenna can exhibit. Not many will go to the trouble to then test with a GPK attached too, but that will show you something. Maybe you can't see a difference in performance, but have some faith in your own common sense that even though you antenna is not flat matched over this extended range that by reducing that range you are improving the radiation effectivness in the antenna by directing more RF into the sky or to the horizon instead down to the ground on you feed line and supporting mast.
Marconi |
Hollowpoint445
Senior Member
Username: Hollowpoint445
Post Number: 1112
Registered: 6-2004
| | Posted on Tuesday, February 28, 2006 - 5:20 pm: |
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Is there an advantage to using radials longer than 1/4 wavelength? I came across a website where they ran a modeling program with 5/8 radials on a 5/8 antenna and saw a lower angle of radiation. The radials were drooping quite a bit - well past 135 degrees to the radiator.
What came to mind was using guy wires as the radials whether or not they were needed for support. |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1240
Registered: 9-2004
| | Posted on Tuesday, February 28, 2006 - 6:29 pm: |
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i believe that the only antenna experiment that is worthwhile is one that is based on solid antenna theory.
i was wondering whether the radials were 5'10" because thats the length that works best, or if they shortened them down from 1/4 wavelength to make them easier to ship.
well, from the responses here, i can determine that the difference is negligable, so it probably is the longest length that can be shipped without an additional charge.
from reading the IMAX EXPOSED article; i have learned that the counterpoise is much more important on the IMAX than it is on the A99.
if i get one i will just buy it and bend it up to the recommended 30*.
the only problem now it that i dont think my property is big enough to put an IMAX up in the air enough to make a difference over the astroplane.
anyone reading this, please refer to the thread titled, "TVI concerns with Top One".
thanks to all for helping me figure this one out,
matt |
Marconi
Advanced Member
Username: Marconi
Post Number: 618
Registered: 11-2001
| | Posted on Wednesday, March 01, 2006 - 1:18 am: |
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Matt, I will mention another thing that comes to mind in your decision to go with the Imax over the AP. If you could possibly have them both up at the same time and hooked to a good switch box, I think given time you would realize one very important difference between the two. The AP may not show quite the signal, as I have explained, but if the AP is not quiter by about 3-5 S-units most all of the time then you are the exception rather than the rule and you have control over conditions at your location, so go fast to get the Imax up.
I have a simple Marconi that is on a 10' mast. A 1/4 wave whip on a mirror mount L-bracket, with three 1/4 wave whips screwed into a hub off of an A99 GPK, and all three are hanging out at 90 degrees. This antenna is also modified other ways as you will see if I can get some pictures on this forum and that to may make some difference in my reports.
I also have an Imax up at three sticks of a pushup pole, about 27' to the base. I am amazed at the local signals that hit this 27' high Imax with an S9 while I get and S8 on this little antenna at only 10' to the feed point. How much difference is that in comparison, I guess you would say not much? And you would be right.
I will send you some pictures of this modified 1/4 wave ground plane with the Imax in the back ground tommorrow if the lighting will work for me in the AM, and you too will see what I have here. At this point you will just have to take my word for the signal reports for the moment, because I have not figured out how to download video to this forum yet. But I am not going to lie to you guys and I do experiment with this stuff too much of the time.
You guys need to experiment with your stuff if you are interested in how it all works. There will be mistakes and misques, you will have one idea one day and something else another, but there is no subsitute for some good hard work at thinking, studying, and experimenting with this stuff. That is the real world. The BS we often here is just that, and that is not the real world.
Marconi |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1247
Registered: 9-2004
| | Posted on Wednesday, March 01, 2006 - 5:19 pm: |
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as much as i want the IMAX; the YL's and my decision to stay at this house for another year makes it impractical.
darn!
the house we were looking at had a back yard that was 3/4 of an acre!
here i have to be realistic about the safey and damage to a neighbors house.
i think the AP is my best friend in this respect.
i wish i could put up both, but i cant at the moment.
still going to try to build my own too, but this will also have to wait a bit.
thats ok; more time to learn,
matt |
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