Sunday, September 02, 2012

In The Beginning

View From The Top
By now most of you that are fans of amateur radio, are aware that I recently purchased a new vehicle, and although I have mounted all my radios and antennas in and on it, I have moved forward with the designing and building of a new antenna.
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.
Your getting a look at some of the materials that are being machined in my shop, as part of a new 10 thru 80 meter HF antenna. This antenna will be quite unique, as I have not seen another of its type available in the marketplace. Whats different about it you ask....Well if you look close, you will notice the assembled mast assembly is of two different diameters. As the photo shows, the mast assembly (the length of the lower mast will be somewhat shorter than in the photo) is sized for a 3 inch coil at the top end of the mast assembly, but the lower section of the mast is only 1.375"OD. When the antenna is complete, the coilform will consist of 2 different sized diameters, allowing for the upper 3 inch section of the coil carrying the tinned buss wire & the whip, to be stabilized by the lower Delrin endcap that will reside within the lower mast. When operating on the lower bands such as 80 meters, this will allow for a very well supported 3 inch diameter sized coil, although with a pleasing overall appearance due to the smaller sized lower mast.

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 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.
 If you were wondering why the two sections of the lower endcap assembly are of different colors, it is due to the fact that I sourced black Delrin for the upper end cap that will be visible, and I wanted it to be black in color or esthetic reasons. Therefore I used the same black Delrin to machine the lower endcap from. However, the material for the tail section of the lower endcap is also Delrin, but I had it in white, and that id why I used the 2 different colors. Just so you know, both the black & white Delrin are RF transparent, although the white is more RF transparent than the black Delrin above 1 ghz.
Hey...the coil fits, now to wind the coil. If you think all this is taking time, your right, as I have a full plate, what with playing ham radio, photography, and all of my other interests, including a little work once in a while.  But stay tuned, as I plan on having this antenna finished sooner than later.
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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