Topband: Low band antenna project questions
w2sh at msn.com
Mon Mar 7 12:32:34 EST 2016
Given the 50' maximum height of a presumably level catenary line supported at its ends, there are two things you can do to significantly improve the performance of the 50' vertical wire hanging below.
1. Obtain a stout piece of bamboo. Try to make at least a 10' long pole, and this may require using two bamboo pieces butted together. Make two rope bridles. Attach the ends of both to opposite ends of the bamboo pole. Make sure that the length of each bridle is such that when both are pulled taut from each bridle's center, a square pattern is formed. Using a goodly quantity of light-weight wire (#26 stranded copper that has a modest coating of pvc insulation is a suggestion), make yourself a reasonably dense top-hat by running lengths of the chosen wire out in rays, with each ray extending to the perimeter of the rope bordered square that you've formed. Then run the same gauge of wire around the square perimeter of the rope square. Using lead-free solder (recommended is 96% Sn, 4% Ag), solder all the rays together at their center, together with the top end of your vertical antenna wire, and each junction of the ray ends to the perimeter wire. Use GE's pure silicone black caulk, daubing some on every soldered joint. All this work can be easily done at ground level, after having first driven in a couple of ground stakes at the center of each rope bridle to keep the bridles taut in their intended square configuration. Break your catenary line at the point where you want your vertical wire to hang. Attach each inner end of the catenary line to the center of each bridle rope. Elevate!
2. Use a much shorter bamboo pole and appropriately shorter rope bridles. Attach a self-supporting length of light-weight aluminum tubing to the center of the pole and connect that to the top of your vertical antenna wire. Fasten the bridles to the split catenary rope as in no. 1.
My preference is for no. 1. This because the taller a vertical antenna, the more it needs longer radials to harvest radiation splashed off the ground for recycling back to the antenna's feedpoint. Because you are limited in the length of your radials, a shorter capacitance top-loaded vertical will play better than a >50' tall vertical.
Have a look in the QST archives for the picture of Jerry Sevick's eight-foot tall 40-meter vertical wearing a very large top hat.
> From: nc3z at outlook.com
> To: topband at contesting.com
> Date: Mon, 7 Mar 2016 15:28:08 +0000
> Subject: Re: Topband: Low band antenna project questions
> That is the highest I can get support for. I am in far eastern NC and
> right on the sound where we get hurricanes and nor'easters so I am not
> putting up the towers I had at the old QTH.
> Gary Mitchelson
> NC3Z/4 Pamlico County, NC FM15
> On 07-Mar-16 09:49, Robert Harmon wrote:
> > Gary,
> > Are you restricted to 50 feet high max ?
> > Bob
> > K6UJ
> > On 3/7/16 5:50 AM, NC3Z Gary wrote:
> >> OK, still working on my permanent low band antenna and what I can fit
> >> for an effective antenna. The space I have is a recently cleared forest
> >> area. I had originally considered a full size loop but the best I could
> >> do is 50' high, although that would be a bit higher than my temporary
> >> dipole it is not much in the scheme of things. And I keep getting talked
> >> out of it.
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