K3ZXL - Super Vertical for Low Bands
Dan Schaaf
7 July 2010


Introduction and Design Philosophy

Step 1- Traps

Step 2 - Insulated Base Design

Step 3 - Tower and Stinger

Step 4 - Raising and Lowering Gin Pole Fixture

Step 5 - Stubs for 30 and 40 Meters

Step 6 - 160 Meter base loading

Step 7 - Bias T remote switching

Step 8 - Drawings

Introduction and Design Philosophy:

Let me begin with the fact that I live on a city sized lot and I have a space on one side of my house that is 35 x 65 feet for antennas.

For several years now, I have used a variety of antennas for low bands. For 30 and 40 meters, my workhorse has been the HyGain AV-640. Terrific antenna !!! Worked lots of DX worldwide with it. But, no bands lower than 40 meters. On 80 meters I first used and inverted V G5RV, then an inverted V Alpha-Delta DX-LB ( 80 and 160 ) and finally a Hustler 6BTV for 80 meters. On 60 meters I used the G5RV inverted V with a tuner. On 160 I used the G5RV inverted V and then bought the Cushcraft MA160 V vertical. The Inverted Vees were too low for optimum performance. The 6BTV was a short antenna and therefore a very narrow bandwidth The MA160V worked the best for 160. But, too many antennas in a small space. So, my goals:

1) have one antenna that would cover 30 through 160 and remove the other antennas.

2) have a robust antenna because the wind speeds here prior to afternoon rains can get up to 50 MPH gusts.

3) have full quarter wave for low angle radiation.

4) ability to raise and lower it single handed in the event of service, approaching Hurricanes or Lightning Season

5) wide 3:1 SWR Bandwidth that can be tuned by my autotuner in the shack

This webpage will describe how I accomplished all of my goals. I did not do this alone. I had extensive assistance and education from Greg Ordy W8WWV and Wil Caselli K1MIJ.

I started this project in the late summer of 2009. A local ham in Ft. Myers Florida had given me 22 ft. of tower that is 9 1/2 inches leg to leg. This was the beginning of my motivation. Originally, I had thought about making my own copy of the HyGain HyTower. After some initial studying of how the HyTower works, I decided that it was not the right thing to do. The HyTower stinger is insulated from the top of the tower and this may have merit in the HyTower design, but it was not the best solution for my application. So, I decided to make the stinger mechanically and electrically connected to my freebie tower.

I was really gung ho until I was diagnosed with cancer which was a real setback in terms of motivation. So, after part way through the project, I put it aside for a few months during treatments. In January 2010, I got back into the project. The project actually diverted my attention from my medical problem.

Step 1- Traps Before starting this project I had to first find out about making a trap for 60 meters. I had read about Coaxial Traps and found a website during my planning for a 160 Meter Receive Loop http://k3zxl.com/Loop.htm . This website belongs to W8WWV http://seed-solutions.com/gregordy/Amateur%20Radio/W8WWV%20Experimentation.htm and he helped me with my Loop Design. Then I had asked him about coaxial traps and he had lots of useful info to convince me that it was the way to go. http://www.seed-solutions.com/gregordy/Amateur%20Radio/Experimentation/CoaxTrap.htm and http://www.qsl.net/ve6yp/ for the software download. Of course, it is not all that simple. You have to know about traps in general. First, in the case of a 60 meter trap on an 80 meter radiator, 60 meters is very close in frequency to 80 meters. Therefore, it is best that the trap be high resistance in the center of the 60 meter band. Some traps on commercial antennas make use of the inductive or capacitive properties of the trap as part of the overall antenna design. The inductive component can be used as loading for the next lower band to keep the antenna short or the capacitive component can be used to allow the antenna to be longer on the lower band. We chose to make the trap high resistance in the center of the 60 meter band to minimize the influence on the 80 meter band.

So, based on that decision, Greg made a 60 meter trap for me using RG-59 and a PVC tube with PVC caps and a 1 inch diameter fiberglass rod for support which would be inserted into 1.125 inch aluminum tubing top and bottom. By the way, Greg has all of the necessary test equipment and modelling software to analyze the final trap to insure that it meets the required specifications. Equipment and software which I do not have.

Step 2 - Insulated Base Design Next was to design an insulated base mounting. For this insulated base, I chose to use the HyGain HyTower base insulators since they are easy to get and a well proven technology. These insulators are made from fiberglass filled epoxy. They are pre-drilled and ready to use. I also bought the tubing that inserts into the bottom of these isulators from HyGain. It is a thick walled tubing. The HyTower uses 3 of these insulators mounted to a triangular base plate. I decided to go with 4 insulators to increase the strength. I had the tubing welded to a 1/4 inch thick plate which is then bolted to the concrete base. I chose aluminum because when water sets under neath or on top of it, it does not corrode like steel will rust. And I left a 1 inch air gap underneath between the plate and concrete to allow water to run off and evaporate.
My base plate is made of 1/4 inch aluminum because I did not want rust to develop on that base plate and because the aluminum tubing from Hygain could then be welded onto the base plate. The tower plate is made of 3/16 inch steel with tabs welded onto it for tilting and supporting the tower legs.

Next was to install a DX Engineering VFCC Vertical Feedline Current Choke under the upper insulated plate. This VFCC chokes off RF from the coax shield and forces return currents to flow only on the radials.

Step 3 - Tower and Stinger
In an effort to help minimize wind loading, several approaches were used. The first was to buy the MFJ/HyGain 1 inch diameter aluminum tube that has supports installed for attaching a CB whip on top. This whip serves to reduce some of the wind loading at the top of the antenna. Secondly, the aluminum tubing is triple and double walled from the top of the tower on up and eventually single wall near the top.

Step 4 - Raising and Lowering Gin Pole Fixture
I also wanted to be able to raise and lower this antenna myself with nobody else available. Why? Because I do things a little bit at a time and I cannot depend on having assistance 24/7. Secondsly, in the event that a hurricane may be on it's way, it would be foolish to expect a neighbor to help you with your antenna when he is primarily concerned about boarding up his house and getting out of Dodge City.

This base plate is not square, it is rectangular. This allowed me to make a support for the permanent gin pole which will raise and lower the antenna. The gin pole is a 20 ft long steel pipe which is hinged at the base so that after the antenna is raised, the gin pole can be lowered to the ground using the same hand winch. The gin pole has a back stay connected to a ground anchor. This stabilizes the gin pole during raising and lowering the antenna. During the first excercise at raising the antenna, I found that the aluminum base plate was warping from the stresses transmitted to it by the gin pole. So, I went back to the welder and had him put a truss on the pole support as well as a 1 inch square aluminum T brace under the plate in a cross fashion to beef up the plate, both fore and aft as well as side to side.

Step 5 - 30 and 40 Meters

A 30 meter stub is mounted 4 1/2 inch center to center from tower legs. The bottom 6 ft piece is 1/2" OD to allow the upper section to telescope for tuning adjustments.
Due to the length of this antenna I decided that I would make use of it's length to get 3/8 wave on 40 meters. The 60 meter trap is capacitive on 40 meters and so it helps to shorten the length. For additional shortening I put an L network at the base that consists of a 3.1 uH shunt coil and a 120 pf series capacitor.


Plastic Clamps for 3/8" OD tubing McMaster Carr P/N 8871T32

Black Delrin Rectangular Bar 1/4" thick x 1 1/2" wide McMaster Carr P/N 8662K22

Stub Tubing 0.375" x 6' DX Engineering P/N DXE-AT1189

Stub Joints 0.500" x 2" DX Engineering DXE-AT1205

Aluminum Rectangular Bar 1/4" thick x 1 1/2" wide

Ubolts for stub bottom 1/2" Saddle Clamp Style U Bolt DX Engineering DXE-SAD-050A

Step 6 - 160 Meter base loading
Base Loading and Shunt Coil Design http://www.dl5swb.de/html/mini_ring_core_calculator.htm

Step 7 - Bias T remote switching

Now, in order to do remote switching from the shack, a Bias T circuit is used to put DC control signals down the coax. The switch positions are:
A) 160 meters,
B) 80, 60, 30 meters,
C) 40 meters.
160 meters is +12 VDC, 80, 60, 30 meters is 0 VDC and 40 meters is -12 VDC.

Base Loading Philosophy

Since the series combination of the 160 meter loading coil and 160 meter shunt coil has a very high impedance at 60 meters and higher, it was simpler to just leave them in the circuit for all other bands.

There are two fundamental drawings. The first is the mechanical structure http://k3zxl.com/Tower_Vertical/Tower%20Assembly-Model.pdf and the second is the schematic of the system http://k3zxl.com/Tower_Vertical/K3ZXL%27s%2030-160M%20Antenna%20Switch%20Rev.%204.pdf . Both are in PDF format for ease of reading and zooming in. Detailed drawings are available on request. This article is not meant to be a complete construction article but rather an overview that can be used to make your own custom antenna depending on your personal needs.