[TowerTalk] Un-nesting aluminum elements...
Robert Chudek - K0RC
k0rc at citlink.net
Fri Jun 30 22:10:13 EDT 2006
Okay fellows, thanks for all the ideas. I need to let everyone know it was necessary to round up a wench to finally get these two pieces of aluminum apart! (And a mighty find wench she was, I must say!)
On the other side of the element, this joint slipped apart real easy. (This is the side that points True North.) This afternoon I took the antenna down to work on it on the ground. I ended up sacrificing the smaller diameter tube even after soaking the joint overnight with LPS and downing the Coke as instructed. Sears was back ordered on the pipe wrench and I'm not allowed to play with matches so heating the outer tube was not an option.
Once I got them separated, I saw there WAS oxigard (or whatever the grey stuff is called) in this joint, but part of it had hardened like concrete. Other areas were still "wet". I ended up strapping the "thick" end of the element to my Ford tractor 3-point hitch using hose clamps. I was necessary to grip the smaller tube with vise grips... thus the sacrifice. When I spun the smaller tube I asked the wench to pull on the loose end. In about 2 minutes we had it apart. But you wouldn't believe how HOT that tubing got from the friction!
In any case, I salvaged a replacement piece of tubing from an old yagi. (Never throw anything away!) I cleaned everything up and put it back together. I ran some VSWR sweeps with this element sitting on a step ladder. Right now it resonates about 6600 KHz. When I raise it back to the 65 foot level this will move up the band. Just how much I'll report later this weekend. (BTW, when I lay it on the ground, it resonates at 4400 KHz, so 5 feet makes a big difference!)
The first time I put this element up (to chase 3Y0X in February), I under-estimated how much it would shift up in frequency. So the resonance ended up about 7500 KHz. (I think it moved up over a half meg!)
That's what started this whole fiasco in the first place... my desire to lengthen it and get it to resonant in the 40m band! I'm starting with 75 ft 5 in total length this time. If I did my math correct, that should put it on 7150 KHz.
Just why this dipole needs to be so much longer than formula escapes me! (I am taking my measurements at the feedpoint, without coax.)
73 de Bob - K0RC
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