Scantenna ST2 repair

[dave3825]

For the antenna experts.

The scantenna's elements were made of hollow rolled tubing. Mine suffered a broken leg during Hurricane Sandy and I am going to repair it. I wanted to know, if one element is solid aluminum rod, or aluminum tubing that's a different thickness (same outside diameter), and the original is hollow rolled tube, will that have any effect on receive performance?

 

[dlwtrunked]

For the antenna experts.

The scantenna's elements were made of hollow rolled tubing. Mine suffered a broken leg during Hurricane Sandy and I am going to repair it. I wanted to know, if one element is solid aluminum rod, or aluminum tubing that's a different thickness (same outside diameter), and the original is hollow rolled tube, will that have any effect on receive performance?

No difference in receive performance . RF signals are carriered on the sufface of the tubing only. Solid will be stronger and that is its benefit (but will weigh more of course).

 

[dave3825]

Ok, well that's good. Now I have to decide if I should go ahead with the original plan which would cost no money. Was thinking of drilling out the aluminum rivet and inserting an aluminum rod inside and solder or aluminum weld using rods and torch. Then dill that piece and re-rivet. With rod inside that area it would give it more strength in that spot. Then do the same on the other side.

Or just buy an aluminum tube from Speedy Metals for 23 bucks and transfer the rest of the stuff over.

A: 3/8" OD
B: 0.305" ID
C: .035" Wall
D: Length 49"

 

[KevinC]

I’d be careful about adding to much weight to the original boom. I’m not sure it can support much more weight than it was designed for.

 

[iMONITOR]

In some circumstances a solid element might be more susceptible to metal fatigue over time from high winds flexing and vibrating them. The problem with hollow aluminum elements that many of them are split making them much weaker than if they were not split.

 

[dave3825]

I’d be careful about adding to much weight to the original boom. I’m not sure it can support much more weight than it was designed for

I thought about that. Since everything is riveted on to the boom, I was either going to buy a section of square tube with a thicker wall composition and just re rivet everything back or, go the complete overkill route (which I am known for) and fill the whole boom with West Systems Epoxy which would give it incredible strength. That stuff has a compression strength of 11,000 pounds per square inch, and tensile strength around 7,000 psi.

The original elements are 49 inches each. Not sure of their individual weight. The weight of a new 60" piece is 0.2220 lbs or 3.552 ounces. A 49" piece should weigh 0.1813 lbs or 2.9008 ounces.

In some circumstances a solid element might be more susceptible to metal fatigue over time from high winds flexing and vibrating them. The problem with hollow aluminum elements that many of them are split making them much weaker than if they were not split.

Thought about that also. Trying to find some lightweight fiberglass rod, similar to plow markers everyone puts out in the winter and inserting them into the full lengh of the elements. Then it should be pretty strong. But then again, if I go with a new section for the element, it is hollow tube without the split and should be better than what it came with.

I saw this pic below in the wiki where some taped a long fiberglass thingy onto theirs but I really don't like the look. So inserting it inside the tubes may be the answer. Whole thing might be over the top but it would take more than Hurricane Sandy to mess this one up.

 

[iMONITOR]

Thought about that also. Trying to find some lightweight fiberglass rod, similar to plow markers everyone puts out in the winter and inserting them into the full lengh of the elements. Then it should be pretty strong. But then again, if I go with a new section for the element, it is hollow tube without the split and should be better than what it came with.

I saw this pic below in the wiki where some taped a long fiberglass thingy onto theirs but I really don't like the look. So inserting it inside the tubes may be the answer. Whole thing might be over the top but it would take more than Hurricane Sandy to mess this one up.

You might be on to something! I think that's what Diamond did with the long lower elements in tehir D-130 discone. Stainless steel tubing with a fiberglass core.

 

[dave3825]

So I have come up with a plan for this repair. Turns out that the inside diameter is 5/16 and Amazon has 5/16 x 12 in rod and 0.035 tube for 3 bucks.





I did not want to replace the rivet, but since its old and weathered, and because I wonder how good of a connection the element to the aluminum wire actually is, and because the plastic insulator would melt in a heartbeat, it looks like I am going to drill out the rivet, then cut a piece of rod 3 inches, drill it for new rivet and weld er up with low temp aluminum welding rods. Might grind out a little bit of the seam to get more welding rod to melt into there for more penetration, or I may drill a few holes in the element every 90 degrees, then slide in the rod and weld, also ensuring a good sturdy conductive connection. The foot of rod weighs 0.090 so divided by 12 then multiplied by 3 = 0.0225 which is 10 grams.




I do have a few tv antenna elements that are the same thickness and diameter but then I have to drill out the rest of the rivets. The former will add strength to the weak point where these seem to break. If all goes good, then I will remove the rivet on the other side and do the same. Worst case, I still have spare elements if needed.