Slingshot Antenna Launcher

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Slingshot Antenna Launcher

Post by va3ts » Sat Jul 29, 2017 12:00 am

This will be revision 2 of the antenna launcher. The first attempt R0 had the reel mounted straight out front on the same plane as the slingshot. R1 had the reel mounted on the side of the slingshot, and this one is out front again but mounted lower on a plane below the slingshot. All three attempts result in a less than 100% successful shot rate. Often the fishing line gets tangled among the rubber bands.

It seems that once the bands are drawn the line itself becomes slack . The key may be to minimize the amount of line drawn by mounting the reel on the same plane behind the reel, or on a plane above the reel.

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Re: Slingshot Antenna Launcher

Post by ve3efq » Wed Dec 13, 2017 3:43 pm

I have since adopted this method for my antennas in my camps given that this is the easiest way to get my wires high in the tree. I hate trying to throw lines up into trees - for hanging food in bear country or trying to get a dipole up: it tangles, it goes up but not down; it goes in the wrong spot and so on. But the slingshot method makes it very easy, with pretty good aim, and gets the line higher than I could throw.

Given that I am backpacking everything, I tried the slingshot method without the fishing reel to save weight. I bought a new spool of fishing line and shot it up in the tree. It worked fine the first few times; but, after manually re-spooling the line a few times it would not un-spool easily; it kept getting wrapped up in itself; the shot was pulling the entire spool off the ground thereby destroying the upward movement of the line. So, it was obvious that the fishing reel was going to be required to maintain free un-spooling of the line.

After Rob's forum post and seminar on 4nec2, which prompted me to learn how to use that program, I compared the vertical radiation plot of my dipole antenna at the height of my telescoping pole, which gives the feed point a height of only about 7.6m:


Here is the model when the height is 12m above the ground:


Here is the model when the height is 20m above ground:


The pole's height works - a year's use of it exclusively shows that; but, obviously, the slingshot method will make a big difference in the performance of the antenna, especially for long ranges. Though, for the 40m and 80m sections of the antenna the model does not show much difference over that range of height changes for those bands.

When I have been using the slingshot, I have been simply leaving the reel on the ground just in front of me rather than mounting it on a bracket (for it is easier for me to pack and carry it this way) and it has been working fine. So, it is possible to omit the bracket mount altogether.

I was only carrying about 12m of coax given the height of the pole and the short run required to my shelter. But, after using the slingshot, I actually ran out of coax before I ran out of height - it was funny to see my 'long' coax hanging above my reach. I have since added coax to my kit - now I have 25m - to take advantage of the new height it is possible for me to get. I am fairly sure that I could even shoot the line higher if in the right spot - some of the places I camped in Algonquin park have trees that are 2 or 3 times the height of the trees around here - so, I certainly would need more coax for that. This should help my 20m DX for sure.


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