WB4IUY's Random Blog

I've been in Amateur Radio since 1974, and still find new and interesting things to do. I like to build, restore, and operate on the air. This is a blog of various info about my Ham Radio operations and activities, projects, and opinions. Visit www.WB4IUY.net for the lowdown at WB4IUY.

Monday, November 21, 2016

Assembling a Low Band Dipole Support....

Well, winter is upon us, and my tower still isn't finished. With lots to do, and cold weather coming fast, I decided I should probably get something up for 80 & 40 CW...fast. I'll still be working on my tower over the coming weeks, but have been in a bad way for antennas since the tower damage on 4/28/16, operating on 40 through 6 meters with my 30m sloper & a tuner.

This is one of the side arms I was able salvage from the tower wreckage. Dipoles for 160m and 80m are heavy, and the previous mount was destroyed, so I needed to fabricate something pretty stout for the job. This side arm looks up to the chore, and will push the antenna feed point about 3 feet away from the tower.

I located a heavy phenolic bar to use as the center insulator, drilled it in the center for a support rope, drilled a pair of holes on either side of the support for stainless steel bolts to be installed to attach the dipole leads, and a hole on either end to anchor the dipole elements to as a strain relief.

I wound a current choke from 8 turns of feed line, about 6 inches in diameter, and attached it to the side arm. A heavy portion of rope hangs the center insulator from the sidearm to support the #14 stranded & insulated wire I'll use for the dipoles. There will be 3 pairs of dipoles (over 300' of wire!) pulling down on this, so the center insulator must be strong and the support must be robust. In addition, the loading goes way up when we have a heavy wet snow or ice storm, not uncommon for our area in January & February.

I use long stainless steel bolts in the center insulator to allow additional dipoles to be easily attached to add more bands and/or bandwidth to this antenna. Initially, it will support two 80 meter dipoles and one 40 meter dipole, in a fan dipole arrangement. This will provide resonant points at 3.525mhz, 3.885mhz, and 7.025 mhz. I'll post more on this, once installed. Here's a few pics of the sidearm, current choke, and dipole support thus far...

This is the phenolic bar I chose to make the center insulator from. I used heavy stainless steel bolts & nuts, and hot dipped galvanized washers to allow attachment of additional dipoles/

Common mode current choke wound from 8  turns of feedline @ 6" in diameter

Choke attached to side arm...

Center insulator hung from the side arm with rope, coax attached to the dipole attachment points

Ready for coax connector to be installed, and be hoisted up to the 70' point on the tower that I have errected thus far...