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Una sola letra y m David J.
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Asunto:[dxcolombia] Loop para 17m
Fecha:Lunes, 11 de Junio, 2007  11:23:01 (-0400)
Autor:Alexis Deniz M. 4M5DXgroup <yv5ssb @...net>

 

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15 Meter HamLoop

Introducing the HamLoop

        Series: L7       

http://k6sgh.com/antennas/L7hamloop.jpg

The HamLoop antenna is a design by me, K6SGH (formally known as kg6ena) and operator of this fine amateur website.  The L7 is the "square" design.  Lots of people call them a "quad" loop.  But like tuna fish, that name seems redundant.

So then the L7 HamLoop is a monoband vertically hung and horizontally loaded square loop.  It is fed with either ladder line, coax and a balun, or coax and a quarter-wave piece of 75ohm coax to the feedpoint.

Using the formula Length=1005/frequency (using 21.375), the antenna is 47 feet in circumference, or 11.75 per side.  A 4:1 current balun is used cut into the center of the lower horizontal element, fed with regular coax.  You can also use ladder line or a quarter wavelength stub of 75ohm coax directly to the same spot on the lower element.  Measured to the feedpoint, the plot on the left is 1/2 wavelength up (23.5 feet) and the plot on the right is a full wavelength up.  For an antenna that is only 35 feet up at the highest point, pattern 1 is a respectable pattern and it really works well.  

img5.gif

img4.gif

An aside here:  Models are models but contacts are contacts.  I set up a 10 meter L7 just for the 10 meter contest in early 2002.  I wanted maximum gain at zero degrees.  Moving the feedpoint around in the model, I found that feeding the loop 15% up from the bottom of one of the vertical elements--in the corner--created this.  So up it went.  It worked great for long DX, but no one in the US could hear me.  In the context of the contest, no contacts was calamitous.  So, I dropped it down, moved the feedpoint to the middle of the lower element, hoisted it back up and off I went.  Not only was I working Japan, but plenty everywhere else as well.  It was like night and day.  That pattern is shown below.   I have used this design quite effectively for DX contests, but it's fairly deaf when it comes to making contacts within the US.

img6.gif

Another nice thing about the L7, is that you can point it.  It is not a beam obviously, but it does have nulls to the side.  Which brings us to how to hang the loop.  I have found that by making a small spar or spreader, you can hang the upper horizontal element from it and use a single hoist point from the center.  HomeDepot carries inexpensive bamboo poles.  An 8 foot length costs about $1.5.  For the 15 meter loop, I took two of them to create a span of 16 feet.  Then simply hung the insulators from the ends of the span and attached a line to the center of the span and hoisted it up into my tree from a single hoist line.  This enables me to "point" the loop by simply moving the tie down lines that are attached to the lower two insulators.  Also, cut a small piece of line 11.75 feet and support the balun or feedpoint from the top of the loop's spar.  This will support the feedpoint and keep the loop nice and square.  Since a picture is always the best, check out the images available from the toolbar.

 

 

 

 


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