Desiring a wire antenna a bit longer than my present 50 foot specimen, I started searching for an easy to build a spud gun that would enable me to run wires through and over the tallest of trees. My slingshot and fishing weights have served me well, but success rates were small and maximum height was limited to maybe 50 feet.
The design was delivered to my mailbox in the March 2009 issue of QST, page 67. W4SSY’s design is based on others I have seen, but his simplified version is just what I was looking for. I already owned most of the parts in my scrap bin, so monetary outlay was minimal. I only had to purchase the water valve and a few PVC fittings. Finding the necessary parts to allow me to connect my Schrader valve and pressure gauge proved to be frustrating, so I used my metal lathe to modify some brass and PVC fittings.
I modified Byron’s design somewhat, driven by my philosophy that bigger is better. Instead of a 12 inch piece of 3 inch pipe, I use a 19 inch piece. My barrel is 36 inches long vs. his 24 inch one. I was concerned that his PVC projectile would be a little light, so I added a small lead fishing weight, bringing my total projectile weight to 3 ounces.
The water valve I selected (Orbit Model # 57101) has a wonderful feature that allows it to be turned on by flipping a small lever 90 degrees. This fortuitous feature means you don’t need a source of power or the extra wiring required to energize the valve. Unfortunately, the solenoid must still be mounted, but that’s a small price to pay.
The first time I fired this beauty up, I decided to start with a pressure of only 20 psi. Since the QST article mentioned an operating pressure of around 35 psi, I figured 20 psi would be a safe starting point. I pointed the barrel up in the air at a slight angle and flipped the lever. With a muted “whummmmmp” the projectile left the barrel and almost disappeared from view. What a glorious sight.
Please reference the QST article for construction details.
Update: I recently retired and moved to a 7 acre "farm" in Northeast Georgia. I participated in the 2014 ARRL Field Day with the Northeast Georgia Amateur Radio Club. I used the spud gun to launch a fishing line over the tallest walnut tree on the site. I built a heavier projectile (4.4 ounces) and pumped the spud launcher to 40 p.s.i. The 4.4 oz. spud cleared the 75 foot tree with no problem, but the entire spool of line was depleted and the arc was stopped short. I was able to tie a nylon string to the end of the line and let the projectile pull the line and the string until I could reach it from the ground. Mission complete.
Inspired by this success, I decided to pre-position a nylon cord for a future wire antenna on my new farm. I replaced the fishing reel with a different model with a larger spool of line. I found a suitable tree, this one about 60 feet tall and took another shot. I should have reduced the pressure a bit because the projectile not only cleared the target tree, but traveled another 110 feet and cleared another 60 foot tree. I should have no problem clearing the tallest tree on my property.