Repairing a Steppir Biggir Vertical – part 5 – Rebuilding the EHU

View of the fiberglass tube after the full-smoke-test. In this view, the arcing appears to stop where the fiberglass tube meets the plastic EHU, but it did not stop there.

This is part 5 of the series of repairing / rebuilding the Steppir Biggir vertical antenna. You might want to start with part 1 here.

I am not going to claim that I know precisely why the parts in the EHU failed. But I will start with Steppir’s statement that “water got in it.” There is nothing to indicated that it could NOT have been water.

You have seen this crude drawing before, in part 4.

Conceptual sketch of the Steppir Biggir construction.

Before I reassembled the EHU with my ‘new’ parts, I thoroughly cleaned the BeCu ribbon with acetone and one of those 3M scouring pads you find in the kitchen. I cleaned the contact(s) with acetone and a toothbrush. I was able to restore both to a nice shiny appearance.

Close-up view of the contact for the BeCu ribbon BEFORE cleaning. The dust is, I believe, residue from various burned items.

I ordered a piece of 1+1/2 inch Delrin 8572k25 from McMaster Carr to replace the internal BeCu ribbon guide, also, a length of 8535k27 fiberglass tube to replace the part of the tube that passes through the EHU. The fiberglass tube comes in 5 foot lengths, so I sure have plenty left over.

Sorry, I did not take any photographs of my ‘new’ parts before installation.

I decided that I would place the o-ring up higher, between the slot for the BeCu ribbon and the fixing bolt. My hope was that any condensation would have to exit via the opening in the Delrin ribbon guide and the fiberglass tube. This would keep moisture inches away from the grounded metal mast.

My idea of moving the o-ring up between the fixing bolt and the BeCu ribbon slot. The idea was that any condensation would have to exit the fiberglass tube where the BeCu ribbon entered.

Unfortunately this did not work, either. I put it all back together and all was fine on 10m through 40m.

However, the EHU failed immediately when I tried to operate on 80m.

WHY did it fail instantly on 80m, but not 40m – 10m ? Very high voltage; this was explained in part 3.

A pleasant ‘surprise’ is that the 80m coil assembly still looks and operates like new.

Here I show the ‘new’ Delrin insert that guides the BeCu ribbon. You can see that I moved the o-ring above the fixing bolt. Because this failed within 1/2 hour of re-assembly, it could not have been water intrusion or condensation.

One of my attempts retained the o-ring, but moved it to be between the fixing bolt and the BeCu ribbon entry point.

Why are these parts burned so badly ? Because I got mad… mad enough that I used an old trouble-shoot technique called “full smoke test.” Yep, apply power as long as you dare, so that when you disassemble the device again, the failure points will be obvious! Once the system has suffered an initial breakdown, it takes “very little” RF to continue the damage, with the rig’s output transistor protection giving me confidence to leave it on at 50 W for about one minute.

Moving the o-ring did not fix anything.

With the original Steppir parts and my “repair” parts, each time, the arc path met the BeCu ribbon on the ‘left’ side. hmmmmm……

View of the fiberglass tube after the full-smoke-test. In this view, the arcing appears to stop where the fiberglass tube meets the plastic EHU, but it did not stop there. The “full smoke test” eliminated any guesswork as to what was not performing.

The outside of the fiberglass tube shows the arcing took the same path on the outside of the fiberglass as it did inside on the Delrin insert.

The fiberglass tube. The “clean” rectangular area is where the the clamp for the “high wind kit” was positioned.

It is not very clear in the photo above, but the arc went down as far as the high-wind-kit clamp and then went horizontally around to the other side. Then went about a 1/2 inch downward and to the metal mast inside.

Sketch showing the arc path in my failure

I do not know what started this failure, but I am now convinced it was not related to water.

Read my final fix in Part 6.

No, really, I fixed it. I think I fixed it for good now…. I have been running 1.5 kW on 80 – 10m for 4 weeks now, including some heavy use during field day. And the fix is much simpler than what you have read about here so far.

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