Contents:
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.
Hardware:
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.
Drawings
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.