Sunday, August 25, 2019

Rebuilding the HF4B

It's been a long time since I picked up the Butternut HF4B project from a friend. I decided it would be a good fit at the Fulton County QTH. It's small enough to be supported by a mast, and will turn with a tiny rotator. I took all of the pieces to Fulton County, disassembled and cleaned everything, and took stock of what I needed.

The basic components seem to be OK. One of the 1/2" tubes is damaged with a gouge near the end, nearly ran over by a lawnmower no doubt, but will be serviceable. One of the 1 1/8" element support tubes has a crack. I've looked for a replacement locally without luck. I think for the moment I'll use a clamp to hold it together.

Two of the four doorknob capacitors have cracked. I managed to find five 75 pF caps at a hamfest a couple of years ago. I bought five in order to have a spare. These things are fragile.

All of the stainless hardware is serviceable despite being out in the weather for over 25 years. The U-bolts, however, are another story.

I don't know what genius thought it was a good idea to sell an antenna with zinc-plated U-bolts, lock washers and nuts. After 25 years of weather, they are rusted junk. Some of the legs broke off when trying to undo the nuts. Those that didn't are so rusty as to be unusable for any purpose.

I ordered replacement U-bolts from McMaster-Carr, who had exact replacements for a reasonable price. Except these are stainless steel.

With replacement hardware in hand, I started to re-assemble the antenna. The wires of the bowtie elements needed replacement. This antenna has eight of these, but only four survived to make it home with me. Of these, only one is intact. I used it to make measurements and make eight identical replacements.

I hit the a snag assembling the first element. The clamps that hold the vertical tubes aren't tight enough to keep them from rotating on the support tubes. Butternut replaced these sheet metal clamps with U-bolts in a later release, which would work better. This requires sleeving about four inches of the vertical tubes.

I guess that's what I'll have to do.

1 comment:

  1. Last year I had a HF5B project. Similair antenna. My HF5B seems to be newer as the doorknob caps are not there. But tuning it is a pain. The antenna is working well for its size especially on 15 and 10m. But compared to other antennas on 20m it doesn't give you any advantage except a lower noise. Good luck, 73, Bas