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1861
Advanced Member
Username: 1861
Post Number: 519
Registered: 2-2004
| | Posted on Friday, June 23, 2006 - 12:16 pm: | 
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IF I USE METAL GUIDE WIRE IN PLACE OF GPK , SHOULD WIRE BE ISOLATED FROM POLE ? |
Marconi
Advanced Member
Username: Marconi
Post Number: 677
Registered: 11-2001
| | Posted on Saturday, June 24, 2006 - 9:48 am: |
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1861, is the GPK isolated from the antenna which is attached to the pole?
I'm not sure about the overall length of effective GP guy wires (maybe 1/4 wave or a bit shorter), but you may need to include some suitable insulators at a point a 1/4 wave or so away from the contact point on the antenna. For sure your guy wires will be longer than a 1/4 wavelength long. It may be possible that longer guys will also work, but you will just have to test that for affect.
When I tested a GPK on an A99, the only thing I noticed was an improvement of the bandwidth with the kit, to a normal curve 1.8 mHz below 2:1 instead of the antenna without being 3-4 mHz wide.
For me this suggest an improvement, even if I could not detect a difference in operations. I did not have these A99's side by side, so my observations were made with some time involved. We all know what that could mean to results. |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1838
Registered: 9-2004
| | Posted on Sunday, June 25, 2006 - 3:05 am: |
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1861, somewhere on here there is a post by tech833 about using all metal guy wires.
i dont want to quote him and risk getting it wrong, but basically he said that as long as the guy wires were below the feedpoint of the antenna, that insulators were not required and the length of the metal guy wires did not matter.
hopefully he will come in here and set us all straight.
if i am remembering correctly, this is great news for a lot of us.
matt |
1861
Advanced Member
Username: 1861
Post Number: 520
Registered: 2-2004
| | Posted on Sunday, June 25, 2006 - 7:48 am: |
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YEAH , I KNOW I,VE READ ABOUT IT HERE AND I,VE DONE A SEARCH BUT HAVE NOT FOUND THAT THREAD . I PUT THE METAL WIRES ON YESTERDAY , ISOLATED THEM ABOUT 12 FT. OUT JUST IN CASE . WILL TRY TO SEE IF IT MAKES A DIFFERENCE . THANKS |
Tech833
Moderator
Username: Tech833
Post Number: 1388
Registered: 8-2002
| | Posted on Sunday, June 25, 2006 - 11:02 am: |
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Again, as long as the guy (not 'guide') wires are under the feedpoint (or lowest part of the antenna in the case of the Top One or Skylab antennas), then they do not need to be insulated anywhere, and length does not matter. |
Road_warrior
Senior Member
Username: Road_warrior
Post Number: 1668
Registered: 7-2004
| | Posted on Sunday, June 25, 2006 - 12:57 pm: |
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What are you having trouble with 1861? Are you using these guy wires for support or for radials? |
1861
Advanced Member
Username: 1861
Post Number: 521
Registered: 2-2004
| | Posted on Sunday, June 25, 2006 - 1:49 pm: |
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NOT HAVING TROUBLE , JUST WANTED TO SEE IF THERE WOULD BE ANY DIFFERENCE ( JUST ONE OF THINGS I DO WHEN BORED ) |
Road_warrior
Senior Member
Username: Road_warrior
Post Number: 1674
Registered: 7-2004
| | Posted on Sunday, June 25, 2006 - 8:40 pm: |
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Oh ok... just experimenting then to keep youself
from getting bored. Gotcha- |
Hotwire
Senior Member
Username: Hotwire
Post Number: 1473
Registered: 1-2005
| | Posted on Monday, June 26, 2006 - 10:41 am: |
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I know just a little about antennas but am soaking up all the good info I can find. I have read in Lou Franklins book Understanding and Repairing CB Radios to keep your guy wires broken up in non resonant lengths. If not they will detune the antenn causing swr problems and radiation pattern problems.Good lengths may be 6 or 12 foot pieces connected with plastic or porcilin egg insulators. The first set should be placed a few inches from the guy wire ring, otherwise the metal to metal contact between the mast and the partial wire "radials" may form a capacity hat which loads the antenna. page 349 |
1861
Advanced Member
Username: 1861
Post Number: 524
Registered: 2-2004
| | Posted on Monday, June 26, 2006 - 5:21 pm: |
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I mounted 4 guy wires at top of mast , right at bottom of i max , and isolated them 12 foot out . Now , I am not going to make any claims , but it does seem to be helping . |
Tech833
Moderator
Username: Tech833
Post Number: 1393
Registered: 8-2002
| | Posted on Monday, June 26, 2006 - 8:03 pm: |
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Marconi wrote, "all antennas between about 1/8 wavelength and one wavelength long radiate close enough to the horizon in order to be effective in 11 meters "
Not so. You know how this works, maximum radiation on the horizon comes from antenna gain and elevation of feedpoint.
Then he wrote, "If it is not so, then how do mobiles work so good compared to base stations, locally or at much longer distances."
Mobiles benefit from huge, solid ground planes under them and very short coax runs, compared to a base station. Maybe it is time to examine what a ground plane really does, excluding the obvious tuning aspect.
Assume for a minute, you have an end fed 1/4 wave ground plane antenna mounted at ground level. The current node is near ground and the voltage node is in the air. Since the current is traveling from the radiator at all angles (down included), much of the signal is either absorbed by the Earth (turned into heat) or, after being slowed by the inductive effects of some inches of Earth, manages to be reflected back into the air at odd phase angles, mixes with the air radiated signal out-of-sync, thus canceling out a portion of the signal on the horizon. The rock skipping on the pond, then beginning to tumble faster than the rock above it that has yet to hit the water- to help visualize.
Now, take the same arrangement and install a solid sheet of metal below the antenna and make sure it is a minimum of 1/4 wavelength long, measured from the feedpoint in all directions. Now, instead of that current being absorbed by the Earth, it flows along the ground plane and adds to the sum of signal on the horizon. Also, no signal is reflected from the ground at odd phase angles because there is no travel distance below effective ground. Any signal reflected off the ground plane will be in phase with signal in air.
Anyone who has ever seen a grid dish knows that you can simulate a solid reflector with individual pipes or wires as long as they are close enough together. As you move them further apart, they act less like a solid form and begin to 'leak'. How much leakage is acceptable depends on the application. Well, let's assume you remove the solid metal sheet and replace it with several wires extending from the base of the 1/4 wave antenna. The more wires (ground radials) you add, the more the system as a whole resembles the solid sheet of metal. More radials (over 1/4 wave long) = more efficiency.
Now, assume we want to get this antenna up in the air to improve the receive capability and reduce receiver noise (and lower the transmitted signal takeoff angle further). Question 1.- How many radials would you need in order to have the same efficiency as the solid metal sheet? Question 2.- How many radials is too many where the wind load, weight, and cost make them impractical? Question 3.- Since we are raising the antenna above ground, which will help the takeoff angle, how much do we lose if we reduce the radials to a manageable number like 3 or 4, and will the height make up for the loss of all the other radials?
These are between the designers and the engineers and the marketing dept. |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1845
Registered: 9-2004
| | Posted on Tuesday, June 27, 2006 - 12:09 am: |
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good lesson!
hotwire, thats funny, i read the exact same page last night while thinking about this.
since we know lou knows his stuff, im guessing that it was an oversight to include the vertical omni antenna in with the yagis, and quads.
or maybe he included it because the info applies to some of the antenna designs that were around when the book was written.
either way, im curious and interested to know what tech833 thinks of this.
paul, hotwire was pretty much quoting from the book in his post if that helps.
as for the guy wires helping the antennas output, if i remember correctly, in tech833's reveiw of the IMAX2000, he said that unlike the antron 99 which doesnt get much benefit from using a ground plane, the IMAX2000 benefited from using one.
i also seem to remember something about the angle of the radials was of some importance too.
like 30* is better than 45*, or something like that.
matt |
Chrisbama351
New member
Username: Chrisbama351
Post Number: 3
Registered: 2-2018
| | Posted on Tuesday, February 12, 2019 - 9:36 pm: |
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I can't find the original post where he explains ground plain radials 30* is better than 45*?
I find a lot of references to the statement tho. I would like to see the proof, test results, the comparison between 30* and 45*. Does anyone have a model showing the antenna pattern of 30* and 45*?
I understand why just want to see the results. |
Tech833
Moderator
Username: Tech833
Post Number: 2426
Registered: 8-2002
| | Posted on Sunday, February 17, 2019 - 1:55 pm: |
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In the 2002 article that was published in Copper Talk and on the Copper Electronics website, I reviewed the Imax GPK (Ground Plane Kit) for the Imax 2000. I installed one on an Imax 2000 and put it on the antenna range and spun it. The free-space patterns were plotted with and without the GPK installed.
What I discovered after doing the article pattern measurements was that angling the groundplanes upward slightly really improved the takeoff angle. It isn't a precise measurement, I just bent them upward and re-spun the antenna until I got a pattern that was optimal. The angle ended up close to 30 degrees. I spelled it out in the discussion that follwed the publication of the original article.
If you are a member of the Copper Forum, you can read it here:
http://www.copperelectronics.com/discus4/messages/7750/20506.html?1023340740
Your radio 'Mythbuster' since 1998
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