Sunday, September 02, 2012
In The Beginning
View From The Top
Now to set things straight, the new mobile HF antenna that I am building will not out perform my existing antenna. I am building a new antenna, to put some of the ideas that I have been carrying around in my head, to metal. Still, I don't believe my new antenna design will take a back seat to the antenna that is mounted on my mobile at the present time, but we'll see won't we.
When I start designing a new antenna, or anything else for that matter, I start by drawing a few sketches including notes in my journal, as this helps me visualize the ideas that I have in my mind, and it moves forward from there.

In this photo, you see the maching underway on the coilform of my new antenna being built in my shop. The material for the coilform is fiberglass tubing, and that presented a interesting problem in relation to cutting the 8 tpi required in this fiberglass tube to wind and keep the tinned buss wire.in place on the coilform.
The previous antennas that I have built in my shop have featured Lexan coilforms, and the maching of the Lexan was straight forward. However fiberglass although a good choice for a coilform, having great strength, waterproof, and rf transparent, does not machine very well. When I say that, I mean in regards to cutting the threadform to hold the tinned buss wire in place, as cutting the fiberglass with a normal cutting tool, would chip the fiberglass, causing a very poor finish, and I wanted to avoid that. After mulling the problem over for some time, I came up with the solution shown here. In the photo, you can see the tool that made this possible. This tool is a Foredom die grinder that has a handpiece mounted on the end of a cable that is turnning at 30,000 rpm. The handpiece has a small precision chuck in which I mounted a carbide grinding burr with the required profile. Once I had everything set up, I made multiple passes in the lathe cutting the required 8 tpi into the fiberglass coilform the depth that was required. Everything went well, with the end result being a nicely finished coilform with the required 8 tpi. Oh, one last thing, cutting fiberglass is hazardous to your health, so do not breath in the fiberglass dust that is being expelled from the cutting action of the cutting tool. I had my shop vac running while the maching was taking place, allowing the capture of all fiberglass dust present around the cutting tool area, or in this case, the grinding burr of the die grinder.Lower endcap with tail section machined from Delrin. fitted to fiberglass 3 inch coilform.


Here is a link to the gallery on my website, where you may follow the progress being made on my antenna.
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