[TowerTalk] Rotator loops was: Re: Feedline for a new tower

[Bob Shohet, KQ2M]

Between the ice and wind at some qth’s like mine, laying cable in loops on a top plate is just begging to have it catch on a corner or be frozen in place and tear.  It is usually a bad idea for anyone to generalize from their qth to everyone else’s, just as it would be for me to generalize from my extreme wx qth to most other qth’s.

As our climate changes, the resultant violent storms become ever more frequent and extreme.  Even with 110 mph wind gusts – reachable now in most of the US  - (the high end of an EF2 tornado or high end of a Cat 2 hurricane) antennas and towers can survive and people might assume that everything else is ok and remained in place, like coax loops.  You know those pictures of cars and small planes being flipped upside down even bad T-storms?  What is the weight of a coax loop compared to that?  All it takes is movement of a few inches to a foot and one end can easily slide off a corner and ges caught with very damaging results.  

For these reasons I have gone with hanging loops with ultimately better results at my qth.  One advantage of a hanging loop is that you can rotate the antenna full scale with someone standing at the top of the tower (or under/above the sidemount) and observe what happens through a 360 degree rotation and make adjustments and then test it again.  And you can, to some degree, simulate the effects of wind by pushing or pulling the loop in different directions to see what it does and move potential obstacles or “loop catchers” out of harms way.  It is not foolproof but it is quite effective.  I have not had anything catch since well before the past two Hurricanes, macroburst and two tornados at my qth, more than 10 years ago.  Of course there is also luck involved.  When Hurricane Irene and its 110 mph wind gusts tore off the massive crown of a tall tree and hurled it into my tower 80’ away, it could have easily have caught on one of the antennas or coax loops or moved them, causing them to catch on something anyway.  You can’t prevent everything, just take sensible and thorough precautions.

I also like hanging loops because ice is far more likely to melt and fall away on a hanging loop when the sun comes out and assists gravity in doing the rest of the work.  This is even more likely to occur if you spray or coat the cable with something that repels water, whereas with a horizontal coil of coax laying on a plate, when the ice melts it can simply refreeze in a blob and stay that way on the cable, freezing it in place.  Many people don’t realize that even when the temperature is > 32 degrees F, if the ice is in the shade, it will take far longer to melt than when it is in the sun.  So no guarantees that the fully ice will even melt when it could, especially if it is frozen into a blob with your cables frozen inside of it.

Bottom line:  Know your qth and the wx at your qth.  And plan for the unlikely events that can REALLY cause problems for you, especially in Winter.

73


Bob  KQ2M


From: john at kk9a.com 
Sent: Sunday, November 11, 2018 10:21 AM
To: towertalk at contesting.com 
Subject: Re: [TowerTalk] Rotator loops was: Re: Feedline for a new tower

That may work if the top plate is large enough. I am not sure what happens
if the coax slips off the edge or how it would work with side mounted
antennas (the majority of mine are side mounted) or with pointy top towers.

John KK9A

From: N4ZR 
Date: Sun, 11 Nov 2018 08:44:44 -0500

I've never understood typical ham practice of a hanging loop.  What Chuck
describes is mechanically much superior.

73, Pete N4ZR
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