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coaxial dipole
On 15 Sep, 19:16, wrote:
I have built several coaxial dipole antennas in the past with great success. What I like about this antenna is it is broadbanded. If you design it using the center of the band of your interest, for the most part you can cover the entire band without retuning. The problem I have always had with this is the antenna is somewhat fragile. I have used plexiglass squares to secure the center of the antenna and taped nylon fishing line to the legs for more strengh. Any one with more ideas? These are mostly useful in the HF range. You can find the info on designing these athttp://www.amateurradios.info and other places on the net. 73's Bill w5grx BILL The best way of using coax with antennas is by stripping the PVC and soaking the braid in polyurothane so the clock wise windings are insulated from the counter wound windings By shorting one end of the braiding you can feed the other end i.e. the two different windings 2where the actual span is somewhat less than a 1/2 wave ( calculate the true wire length) The same can be accomplished by using somewhat less than a full wave length folded back on itself and directly feed the ends. This arrangement takes the fragility away from the span by not feeding at the center as well as using the center wire of the coax for mechanical strength. This method comes in quite usefull when the need is for a 160 meter antenna where you can wind the coax cross wise fashion so the ends for feeding finish together. This comes out at around 60 turns on a 2 foot former. This method gives more gain over 1/2 wave designs in a similar way that a quad or loop of one wavelength exceeds others. You can also use a single wire instead of coax for cheapness if you wish but ofcourse you like coax but this way you can join scraps of coax and solder them together without bothering with individual strands. This method by the way does not require a ground plane so you may leave the barrel on the ground or place it on top of the tower for rotation purposes. You can have a lot of fun with this antenna if you can also rotate the axis of the barrel by useing two rotators or a combination satelite version. Note thatusing a full wave length antenna you achieve tha same gains( ~ 3db) that a quad obtains over the standard fractional WL length radiator(~2db when using single wire). Feed impedance is around 50/60 ohms resistive and is quite broad banded. The above is based around Gausswian formulae that also conforms with Maxwellian laws so you can use suitable modeling programs such as AO to derive all specifications. The above is subject to possible U.S. patents acceptance at this time Enjoy Regards Art KB9MZ....XG |
#2
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coaxial dipole
On Sat, 22 Sep 2007 08:14:58 -0700, art wrote:
On 15 Sep, 19:16, wrote: I have built several coaxial dipole antennas in the past with great success. What I like about this antenna is it is broadbanded. If you design it using the center of the band of your interest, for the most part you can cover the entire band without retuning. The problem I have always had with this is the antenna is somewhat fragile. I have used plexiglass squares to secure the center of the antenna and taped nylon fishing line to the legs for more strengh. Any one with more ideas? These are mostly useful in the HF range. You can find the info on designing these athttp://www.amateurradios.info and other places on the net. 73's Bill w5grx BILL The best way of using coax with antennas is by stripping the PVC and soaking the braid in polyurothane so the clock wise windings are insulated from the counter wound windings By shorting one end of the braiding you can feed the other end i.e. the two different windings 2where the actual span is somewhat less than a 1/2 wave ( calculate the true wire length) The same can be accomplished by using somewhat less than a full wave length folded back on itself and directly feed the ends. This arrangement takes the fragility away from the span by not feeding at the center as well as using the center wire of the coax for mechanical strength. This method comes in quite usefull when the need is for a 160 meter antenna where you can wind the coax cross wise fashion so the ends for feeding finish together. This comes out at around 60 turns on a 2 foot former. This method gives more gain over 1/2 wave designs in a similar way that a quad or loop of one wavelength exceeds others. You can also use a single wire instead of coax for cheapness if you wish but ofcourse you like coax but this way you can join scraps of coax and solder them together without bothering with individual strands. This method by the way does not require a ground plane so you may leave the barrel on the ground or place it on top of the tower for rotation purposes. You can have a lot of fun with this antenna if you can also rotate the axis of the barrel by useing two rotators or a combination satelite version. Note thatusing a full wave length antenna you achieve tha same gains( ~ 3db) that a quad obtains over the standard fractional WL length radiator(~2db when using single wire). Feed impedance is around 50/60 ohms resistive and is quite broad banded. The above is based around Gausswian formulae that also conforms with Maxwellian laws so you can use suitable modeling programs such as AO to derive all specifications. The above is subject to possible U.S. patents acceptance at this time Enjoy Regards Art KB9MZ....XG Art, I'm curious concerning what kind of mind-enhancing substance you were on when you wrote the above post. As far as I can tell, this post concerns the coaxial dipole. However, I don't discern any relationship between your post and the coaxial dipole. What does "60 turns on a 2 foot former" have to do with the coaxial dipole? And what is the "barrell" that you can leave on the ground or put on the top of the tower for rotation purposes? Rotation of an 80-meter dipole with a barrell on the top of the tower? Art, you have been smoking too much liquid polyurethane in your Gaussian pipe. Walt, W2DU |
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