Repairing a Steppir Biggir Vertical – part 5 – Rebuilding the EHU
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.
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.
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.
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.
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.
With the original Steppir parts and my “repair” parts, each time, the arc path met the BeCu ribbon on the ‘left’ side. hmmmmm……
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.
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.
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.