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  #9  
Old 03-20-2012, 05:00 PM
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Quote:
there's no such thing as a "quarter wave coil"
In the case of that antenna, and the A99/Imax 2000 antennas, yes it is used as part of the matching network.
It is a common misconception that you can unwind a ( for example) a coil in a center loaded antenna and the length will be the "missing " length of a 1/4 wave or 5/8 wave antenna.



This is From Tom`s (W8JI) Web page that can be found @ Mobile antennas, short verticals, loading coil loss,and loading coil current


Quote:
Common myths about inductor behavior:


We often find inexperienced builders of 5/8th wl antennas think the "loading coil" needs to contain 1/8th wavelength of wire in order to make the 5/8th wave antenna a "3/4wl resonant antenna". They think, through wire length alone, the wire creates a low feed impedance by making the antenna three-quarters of a wave long electrically. In other cases claims are made one half-wave of wire wound on a compact form causes a 180-degree current delay, making a compact coil useful for phasing in a collinear array.

The basic flaw is the above ideas do not account for what actually occurs in a coil. The flawed viewpoint is current goes in one end, winds its way around through the physical length of wire in the coil, and after a time delay caused by the copper path length current appears at the other end. There is a physical mechanism that prevents what we might intuitively think happens from actually happening. A coil or loading inductor has magnetic mutual coupling between turns. The physical mechanism is the magnetic field in the coil!

What Really Happens

When current flows in the transmitter-end of the coil, a magnetic field is created. This time-varying magnetic field causes charges in the other turns to instantly move. This effect ripples through the length of the coil at light-speed, just over 186,000 miles per second. As long as the magnetic flux coupling is high, the delay through the coil is the speed of light over the physical length of the coil. In an inductor with good flux coupling from end-to-end, the electrical time delay in current is very close to the physical length of the coil expressed in degrees at the operating frequency. Note that this time delay is NOT the phase relationship between voltage and current, but the delay time of current appearing at each inductor terminal. More on this appears later in this text.
Tom Has loads of good reading on his Antenna pages.


73
Jeff
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Old 03-21-2012, 04:17 PM
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Ok well maybe I did not word it right. I have never taken any electronics classes so I don't know the proper terminology.
But it is theoretically possible to use a loading coil to electrically reduce the length of an antenna.
A friend wanted an 80 meter dipole in his back yard, but did not have the room for 2 65ft legs, so he opted for a shorter version that had 2 loading coils which reduced the overall length.
Tom W8JI needs an interpreter to put his info into laymans terms for us idiots that never took electronics classes.

Last edited by W5DMG; 03-21-2012 at 04:36 PM.

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  #11  
Old 03-21-2012, 04:35 PM
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I was quoting Doc, but don`t worry about the proper terms.
When I first started playing radio, I was convinced that a loading coil did "make up the length" of the Antenna, took me a bit to grasp the concept.
W8JI has some really good reading on his web pages.


73
Jeff
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Old 03-21-2012, 05:58 PM
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"Extraterrestrial Admin". So Jeff what is it AMSAT or SETI.?
I am an AMSAT member that also processes SETI data.
Actually I am the AMSAT Founder for SETI.

Last edited by W5DMG; 03-21-2012 at 06:25 PM.

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  #13  
Old 03-21-2012, 06:45 PM
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Lol, No I am not a AMSAT Member, and although I have visited Berkeley, and I have always loved science, I have never been to the SETI Institute.
Are you part of the SETI@home project?
If I understand correctly, it allows the project to use individual`s home computers to create sort of a giant "supercomputer" that is all connected together, and helps to analyze data collected from radio telescopes used in search of signals from other worlds.
Am I close?
As for Tom`s web pages......I read them and go away and try to wrap my head around it, and come back and read some more....I doubt I will EVER fully understand antennas the way some do, but I do my best to try.


73
Jeff
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  #14  
Old 03-26-2012, 04:36 PM
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I just gave mine to a friend of mine who has it mounted on his garage. It works quite well.

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Old 03-30-2012, 03:48 PM
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Quote:
Originally Posted by WB2WIK
I own that, and have assembled many of the Ringos over the years including the 10m model.

It does "work," but has serious common mode issues because it really, really needs radials! You might note that the 2m high-performance version of that same antenna, Cushcraft model ARX-2B, does have radials -- and boy, do they help...a lot.

They didn't use them on the 6m and 10m versions only to minimize cost and the amount of space required for installation; but with the 10m Ringo, the mast you mount it on becomes a single radial (which does help, to some extent) below the feedpoint. If the mast is 1/4-wave long (about 8-1/4 feet), the antenna acts like a offset-fed dipole and does pretty well. If the mast is some other length, the outer conductor of the coaxial feedline becomes an undesired radial and causes problems for most. If mounted on something non-conductive like PVC or wood, the feedline always becomes an undesired radial and the antenna can, depending on line length and orientation, have a lot less than 0 dBd gain. It could have -6 dBd gain, easily; and often does that.
I am curious if the Proton uses the mast in the same way as the Ringo, since the Proton has no radials.

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Old 03-30-2012, 06:14 PM
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I am shocked to see this still going but anyway I gave this antenna to a friend and ended up putting a Imax at both the home and cottage. In time I am going to take both down and put a Maco 103-c under both with a rotor. I like the Imax for finding DX and then switching to the beam for distance and less noise. I am still running no amps here.
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