Homemade Open Wire Feedline
.
With a few simple
tools and a little effort you can make your own open-wire
line that is superior in many ways to the "window line"
that is commonly sold by antenna product vendors. My
biggest complaint about "window line" is that when the
weather turns foul, the loading characteristics of the
antenna change drastically due to moisture contamination
of the plastic surfaces between the parallel wires. As a
result, it becomes necessary to frequently adjust the
tuning during sloppy weather as rain, snow, and ice begin
to collect on the plastic. Another annoyance is that
"window line" has a tendency to catch a lot of wind which
causes it to whip around. At my location, this frequently
causes it to get tangled up with nearby branches. The
worst issue, however, is with the fragile nature of the
solid conductor type of "window line". Over time, it
inevitably forms breaks in the solid wire conductors from
the stress of movement as the feedline swings back and
forth. Obviously, this inconveniently results in half of
the antenna disappearing from the load, which can have
catastrophic results if you run power.
Peter - N2IDU mentioned to me during a QSO that he had come up with something that worked very well for open wire spreader material. A company called Fi-Shock sells a line of inexpensive electric fence insulators that are very strong, rated to handle high voltage, transparent to RF, and are resistant to ultraviolet exposure. There are many ways you could assemble open wire with the Fi-Shock insulators but I went for simplicity and strength. The homemade open wire line line shown here is stronger, less likely to be affected by wet weather loading issues, and offers much less surface area for the wind to play with. The degree of difficulty for this project is very low, the list of required materials isn't long or expensive, and the materials are readily available:
1. Insulated stranded wire. I purchased a 500 foot spool of black insulated #14 THHN at Lowes (40 bucks on sale) and used that for the feedline and the 250' center-fed antenna.
2. Fi-Shock 4"ribbed tube insualators. I grabbed a box of 200 for 17 bucks (plus about 9 bucks shipping) online at: Fi-Shock Online Catalog Several hams have found them locally at Tractor Supply.
3. A drill with a 1/8 inch drill bit.
4. A vise or a suitable clamp to hold each insulator in place as you work on it.
5. Wire cutters for slotting the end of each insulator.
6. A hot glue gun and glue sticks
That's all you need to get the job done!
The Fi-Shock insulators are UV resistant and built for use outdoors with high voltage electric fences. They are durable and rigid enough to hold your feedline wires very securely. The 4 inch insulators are sold in boxes like the one in the picture below:
To prepare a Fi-Shock tube for use as a feedline insulator, clamp it by one of its ribs in a vise, and then drill a hole at each end through the tube with a 1/8 inch drill bit. Using a magic marker, I made guide marks on the top of the vise to line up my drill bit with so the holes would be a little less than 1/4 inch in from each end. Use a pair of wire cutters to snip from the end of the insulator to the hole that you drilled to allow you to snap the insulators onto the wires. Obviously, you need to make 4 snips to complete the job.
The number of insulators you need will be determined by the length of your feedline and whatever spacing between insulators you feel is adequate for your application. I use one foot spacing between insulators, and my feedpoint is 70 feet above the ground, so I made 90 insulators to allow for a vertical drop of about 60 feet and 30 more to get over to the house. Many people use 2 foot or even 3 foot spacing and have no problems with feedline twisting. After doing a little testing, I found that using one foot spacing makes it impossible for the feedline to cross over itself, even if the line somehow gets twisted numerous times. I often run full legal limit on the lower bands, so in my opinion, the extra safety factor gained for a small amount of time and effort is a good investment. After preparing about a dozen insulators, I had the process down to a 30 second operation for each one, so this part of the project actually goes pretty fast. When you have prepared enough insulators, tie off your parallel feedline wires to a couple of ladders, or your tower, or a couple of convenient trees to make it easy to snap the insulators onto both wires. As you can see in the picture below, I used a pair of step ladders and a garbage can in the middle to keep the wires high enough to prevent a lot of bending over. Just walk along and snap them on, spacing them as you desire.
Peter - N2IDU mentioned to me during a QSO that he had come up with something that worked very well for open wire spreader material. A company called Fi-Shock sells a line of inexpensive electric fence insulators that are very strong, rated to handle high voltage, transparent to RF, and are resistant to ultraviolet exposure. There are many ways you could assemble open wire with the Fi-Shock insulators but I went for simplicity and strength. The homemade open wire line line shown here is stronger, less likely to be affected by wet weather loading issues, and offers much less surface area for the wind to play with. The degree of difficulty for this project is very low, the list of required materials isn't long or expensive, and the materials are readily available:
1. Insulated stranded wire. I purchased a 500 foot spool of black insulated #14 THHN at Lowes (40 bucks on sale) and used that for the feedline and the 250' center-fed antenna.
2. Fi-Shock 4"ribbed tube insualators. I grabbed a box of 200 for 17 bucks (plus about 9 bucks shipping) online at: Fi-Shock Online Catalog Several hams have found them locally at Tractor Supply.
3. A drill with a 1/8 inch drill bit.
4. A vise or a suitable clamp to hold each insulator in place as you work on it.
5. Wire cutters for slotting the end of each insulator.
6. A hot glue gun and glue sticks
That's all you need to get the job done!
The Fi-Shock insulators are UV resistant and built for use outdoors with high voltage electric fences. They are durable and rigid enough to hold your feedline wires very securely. The 4 inch insulators are sold in boxes like the one in the picture below:
To prepare a Fi-Shock tube for use as a feedline insulator, clamp it by one of its ribs in a vise, and then drill a hole at each end through the tube with a 1/8 inch drill bit. Using a magic marker, I made guide marks on the top of the vise to line up my drill bit with so the holes would be a little less than 1/4 inch in from each end. Use a pair of wire cutters to snip from the end of the insulator to the hole that you drilled to allow you to snap the insulators onto the wires. Obviously, you need to make 4 snips to complete the job.
The number of insulators you need will be determined by the length of your feedline and whatever spacing between insulators you feel is adequate for your application. I use one foot spacing between insulators, and my feedpoint is 70 feet above the ground, so I made 90 insulators to allow for a vertical drop of about 60 feet and 30 more to get over to the house. Many people use 2 foot or even 3 foot spacing and have no problems with feedline twisting. After doing a little testing, I found that using one foot spacing makes it impossible for the feedline to cross over itself, even if the line somehow gets twisted numerous times. I often run full legal limit on the lower bands, so in my opinion, the extra safety factor gained for a small amount of time and effort is a good investment. After preparing about a dozen insulators, I had the process down to a 30 second operation for each one, so this part of the project actually goes pretty fast. When you have prepared enough insulators, tie off your parallel feedline wires to a couple of ladders, or your tower, or a couple of convenient trees to make it easy to snap the insulators onto both wires. As you can see in the picture below, I used a pair of step ladders and a garbage can in the middle to keep the wires high enough to prevent a lot of bending over. Just walk along and snap them on, spacing them as you desire.
When they
are all installed, warm up your glue gun, and as
you walk along one side of the feedline, pump hot
glue into the nearest side of each insulator. Make
sure you inject enough glue so that it flows past
the wire inside the insulator tube to ensure that
it locks the wire in. After you finish with one
side, walk down the other side and inject hot glue
into the other end of each insulator. Again, push
enough glue in so that it flows past the wire. The
second side will be a bit messy, because the air
inside the tube becomes very hot, and as it
expands, it will push the glue back out, but it
quickly "pops" and then pulls the glue back in as
it cools. The nice thing about this process is
that the sealed tubes won't become contaminated
and lossy inside with moisture, bugs or dirt. When
the glue cools, the wire is molded right to the
insulator and locked firmly in place. As a last
step, walk along and inspect each glue joint to
assure that the wire is securely fastened. As you
inspect, take the time to clean off any excess
glue that may be hanging onto the wire. A lot of
spider-web like excess seems to form whenever I
make this stuff, and I found that just wiping down
the wires with my work gloves cleans it all off
easily.
With the feedline finished, solder the leads at one end to your antenna, prepare the other end for your balanced line tuner or balun, and then haul it all up into place. The picture below showing the feedpoint at 70 feet was taken from the roof of my house. The feedline is light and won't load down the center of a dipole like coax tends to do. As the picture shows, my 250 foot center-fed is supported in the center and configured as a gently sloping inverted-vee.
The picture below shows the 60 foot vertical drop and the transition to the horizontal path over to the house. The wind was blowing at about 20 mph at the time and the only movement evident from the feedline was a gentle swaying as the supporting trees and antenna moved around. Air passes right through the feedline so it doesn't whip around like window line which is a good thing as it prevents a lot of mechanical stress.
Outdoors, about 6 feet below the station's window threshold, I run the balanced feedline through an Array Solutions AS309H open wire lightning arrester mounted on a small piece of vinyl fascia board bolted to a 10 foot steel post that is pounded into the ground. A short run of #6 copper wire connects the ground tap of the AS309H to the steel post and its collection of ground rods bonded to its base. After passing through the lightning arrester the open wire feedline continues up to the window threshold and passes through two big feedthrough insulators to the Palstar AT4K antenna tuner. When thunderstorms roll into town, it's easy to disconnect the feedline from inside the house, leaving the antenna grounded through the AS309H to the steel mounting post. I have a feeling that the big wire antenna having a straight shot to ground outside the house is a good thing. So far so good...
With the feedline finished, solder the leads at one end to your antenna, prepare the other end for your balanced line tuner or balun, and then haul it all up into place. The picture below showing the feedpoint at 70 feet was taken from the roof of my house. The feedline is light and won't load down the center of a dipole like coax tends to do. As the picture shows, my 250 foot center-fed is supported in the center and configured as a gently sloping inverted-vee.
The picture below shows the 60 foot vertical drop and the transition to the horizontal path over to the house. The wind was blowing at about 20 mph at the time and the only movement evident from the feedline was a gentle swaying as the supporting trees and antenna moved around. Air passes right through the feedline so it doesn't whip around like window line which is a good thing as it prevents a lot of mechanical stress.
Outdoors, about 6 feet below the station's window threshold, I run the balanced feedline through an Array Solutions AS309H open wire lightning arrester mounted on a small piece of vinyl fascia board bolted to a 10 foot steel post that is pounded into the ground. A short run of #6 copper wire connects the ground tap of the AS309H to the steel post and its collection of ground rods bonded to its base. After passing through the lightning arrester the open wire feedline continues up to the window threshold and passes through two big feedthrough insulators to the Palstar AT4K antenna tuner. When thunderstorms roll into town, it's easy to disconnect the feedline from inside the house, leaving the antenna grounded through the AS309H to the steel mounting post. I have a feeling that the big wire antenna having a straight shot to ground outside the house is a good thing. So far so good...
Note that it
appears that Array Solutions no longer offers
the AS309H open wire surge protector. The DX
Engineering open wire surge protector (Part
Number: DXE-LLSP) appears to have the same
ratings and looks like it would be an equivalent
solution. It can be found here: https://www.dxengineering.com/parts/dxe-llsp
By the way, the same materials and construction techniques work great for building fan dipoles. I assembled a 20 meter and 17 meter fan dipole with the same 1 foot spacing between insulators and it performs beautifully on both bands. It's lightweight, physically strong, and took about an hour to put together and trim to resonance on both bands. The picture below shows the fan dipole stretched between 2 trees at 50 feet above ground. Parachute cord is used at the ends of the 17 meter dipole to tie it off to the 20 meter dipole above it.
By the way, the same materials and construction techniques work great for building fan dipoles. I assembled a 20 meter and 17 meter fan dipole with the same 1 foot spacing between insulators and it performs beautifully on both bands. It's lightweight, physically strong, and took about an hour to put together and trim to resonance on both bands. The picture below shows the fan dipole stretched between 2 trees at 50 feet above ground. Parachute cord is used at the ends of the 17 meter dipole to tie it off to the 20 meter dipole above it.