Saturday, May 12, 2012

Improvised home brew insulator for my Butternut HF-6V vertical

A number of days ago while operating CW on the 15 metres (21 Mhz) band using 400 watts I turned to look out the window while operating and noticed white arcing sparks coming from a point up the antenna. There was some smoke too. I turned down the power but it was still happening. After stopping transmission I noticed the part of the antenna that was affected was an insulator and I could see from the shack that it was almost burnt out!

The burnt out insulator from the Butternut
So I stopped using the antenna immediately. The Butternut is an important part of the setup here, and a vital antenna in working the world. I planned to take it down and examine it as quickly as possible to see what the damage was.

A couple of evenings later I set to work. I decided to take the antenna apart at a point about six feet off the ground. This prevented me having to disconnect coax and all the stay wires (which are made of strong fishing line). I brought the top part of the antenna down to ground and, sure enough, I could see the insulator was almost melted away in parts.

The new insulator in situ
A few months ago I was gifted a couple of pieces of uPVC that had been cut off a chopping board. You know, one of those things that people chop vegetables and fruit on in the kitchen! Yes, this is where domestic culinary implements meet the hobby of amateur radio. When we say "home brew" in this hobby, we really mean it. If it's made from the right material, it might just end up as part of an antenna! I had been given these bits by Pat EI2HX, with the express purpose of making insulators for antennas if the need ever arose. So thank you Pat!

I set to work cutting away a piece, using a hacksaw, that would  be the same length and width as the burnt out insulator. Needless to say it was thicker, but when I finished with the saw I had a shiny white new insulator. I drilled two holes in it, one for attaching it to the aluminium holder on the antenna, and the other to attach the wire running down the side of the Butternut. After a few minutes of tightening everything up, it was all ready to go back up in the air!

The new insulator
It did look immediately different with the new insulator, but nevertheless appearance does not matter - it's performance that counts! With everything reassembled, the jubilee clip and screws tightened up, and amalgamating and insulating tape added, I was ready to see if it was working.

Some quick testing in the shack revealed that the SWR was still pretty much as it had been, with no ATU in line. I had resonance on the bottom end of 80m (about 1.3:1 at 3.505), and a decent SWR on 40m, 20m, 15m and 10m. I even had decent resonance on 30m! I tuned up the Acom 1000 and put a bit of power into it on 15m, running it for a while. No sign of any arcing - not yet anyhow. 

Given that this particular Butternut is estimated to be at least 20 years old, and that it was resurrected from a very sad state in someone's back garden a couple of years back, it is performing very well. Latest DX worked since the repair was 5N7M in Nigeria on 80 metres CW!

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