Sunday, September 30, 2012

Mark III Antenna Launcher

The Mark III antenna launcher.
Trees make very nice antenna supports. Very nice, that is, if you can get a rope over the branches. That's always the tough part.

During one of the W4DOC Atlanta Radio Club field days, I watched some of my fellow hams easily put up temporary antennas with a contraption similar to this one. I had to have one of my own, so I built it.

Two ordinary sporting components are merged together to create this oddball contraption. And for what it is designed for, it works well:

  • Wrist Rocket - also known as a sling shot. Get the kind that uses surgical tubing as the elastic. I believe I found this unit at a K Mart for about $7. I've had it 20 years, and it still works fine. Eventually, the tubing will need to be replaced when it gets cracked and starts to separate.
  • Fishing Reel - the original, or Mark I version, used a closed-face reel that I found for $4, probably at the same K Mart. Mark II upgraded to a 1960 Shakespeare open-face reel that my father-in-law gave me. Unfortunately, the winding handle broke and parts are unobtainium. Enter Mark III - a modern Shakespeare open-face reel for $20 at Walmart.
Wrist rocket and the reel are joined together using a block of wood and a couple of hose clamps. The wood has a channel hollowed in it to fit over the wrist rocket frame.

The open-face reel is important. Although I got a closed-face reel to work, the line had a tendency to bind a bit, which shortened the height and distance I could cast a weight. The open-face reel greatly reduces the resistance of the line playing out.

A bit of advice from using this contraption:
  • Wear Eye Protection! No matter how good a job you do, every once in a while the line will snag on something, and the weight will snap back toward you. You might consider wearing a hard hat and a jacket as well.
  • Use Appropriate Weight. The wrist rocket is designed for relatively small projectiles. If it is much bigger than the pouch, it won't fly right. Small fishing weights work well, but don't spend a lot of money on them. You will lose weights -- it's inevitable. The weight has to be heavy enough to pull the line down to ground level. If the weight won't fall down to the ground, you'll have to reel it back in and try again. I've had success with using 1/4" to 3/8" bolts with nuts.
  • Take Your Time. Pick a good spot and try several shots to get the hang of using this thing. You'll have to aim slightly above where you want the line. You won't always get it in the right spot on the first try.
  • Reel in Slowly. When you mis-cast, you have to reel the weight in. Careful you don't try to do it too fast. As the weight comes up to a branch, it will start to swing, and if you reel in too fast, the weight can easily wrap around the branch. At this point, you have no choice but to pull until the weight comes free, or the line breaks. If you pull really hard, beware that the weight can come back at you like a rocket.
  • Use 10-15 lb Test Line. Some cheap reels come with line. If it isn't a strong line, best to pull it off the reel and use something known. Nylon line is really cheap.
  • Don't haul your halyard directly. Once you have the fishing line over your target, use it to haul up a small rope. I have 500 feet of 1/16 inch braided nylon rope for this purpose. I then use that line to haul up my 1/4 inch dacron halyards. 

An easy project, really. Enjoy building and using your antenna launcher. Just don't go use it when your neighbors are watching....

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