Friday, March 25, 2016

Aim High

Antenna Raising

Last Saturday morning was cool and damp.  What better outdoor activity for such a time than putting up some antennas. 

I had the opportunity to help put up an 80m/40m Doublet at the Excalibur antenna site. My only previous experience at getting antennas in trees was to use a throwing weight with kite line, but Paul Stroud (AA4XX) showed me the finer points of using a slingshot.

Up, Up and... well that didn't go where I aimed

Getting an antenna support through the top of an 70-80 foot tall tree is a multi-step process.  Or if you're new at this like me and miss your mark with a slingshot, a repetitive, multi-step process.  

  1. Attach a fishing reel with lightweight 6 lb fishing line to a slingshot.  Lubricates the line with a very lightweight oil or teflon to let it better slide over branches, especially in the spring when the sap starts to flow.  
  2. Attach a 1-2 oz weight to the line with a snap hook.  You'll be taking that weight on and off the line frequently.
  3. Sight well above the tree and aim for a hefty fork in the branches that you wish to support the antenna wire.
  4. Let it fly...  At which point there are a couple of possibilities:
    • If you are Paul and you've done this many times then you move on to the next step.
    • If you're like me you miss badly a few times, or you tangle the fine fishing line on the launch.  When you miss: 
      • Gently tug on the fishing line watching for where the weight is at the other end. Mark that spot in your mind.  
      • Go detach the weight, come back to the rod,  THOU SHALT NOT try to reel the line back with the weight attached.  If you leave the weight on while trying to reel it back IT WILL wrap itself around a branch and you'll have to cut the line and likely lose the weight.
      • Reel the line back in and try again.
  5. Gently tug on the fishing line to find the weight at the other end bobbing above the ground so that you can find it.
  6. Go to the end of the line that you marked in your mind (you were paying attention weren't you?) and detach the weight and attach 100 lb fishing line to the 6 lb line.
  7. Reel back your 6 lb line now bringing with it the 100 lb fishing line.
  8. Attach your antenna rope (or weedeater line in our case) to the 100 lb fishing line, go back to the other side of the tree and pull it through while re-spooling your 100 lb line.  Getting the heavy line through the branches requires a bit of tugging.
  9. Now attach your antenna to the support line and prepare to repeat the steps for the other side of the wire.

Correcting one of my many blunders.  Homebrew ladder line in the foreground.
In our case we had a 40m dipole and 80m dipole attached to the same insulator so we were raising one antenna with 4 ends.  Ultimately the center feedline height was about 65 feet with the 80m and 40m antennas about 30 degrees off axis from each other.  The 40m antenna was aligned for best propagation to Europe.  The relatively low height of the 80m antenna meant that it was omnidirectional.

The feedline was 125 feet of home-made open wire feedline made from cheap insulated 18 gauge wire and electric fence insulators.  The plastic electric fence insulators had a hole drilled in each end and small zip ties were used to hold the wire in place.  Insulators were spaced approximately 18 inches apart on the feedline.  That's a lot of insulators.  Paul is a patient man.

Other work at the site

While Paul and I were working to get the 80m and 40m doublet raised Dick (N4HAY) was doing an inspection on the antenna  mounted on the 75 ft crank up tower.   The tower had been lowered for maintenance. 

Cranking it back up is a good cardio workout.
N4HAY displaying the proverbial "High Standing Wave"
So I'm learning about raising wire antennas and sharpshooting with slingshots. Fun times.

That's all for now

So lower your power and raise your expectations

Richard, AA4OO

1 comment:

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