Inspired by an article in the March 2009 issue of QST I began building air-powered Antenna Shooters which make it easy to get antennas up into trees.

First Generation Shooter

Above is my first generation Antenna Shooter. it is pressurized by an automobile tire pump to between 30 and 60 PSI. The pressure tank is a 12-inch piece of 3-inch diameter Schedule 40 PVC pipe. The barrel is 24-inch long piece of 1-1/4 inch PVC. To release the air into the barrel I use a 1-inch PVC Globe valve. It launches a 2-1/2 inch PVC projectile constructed out of a piece of 3/4 inch PVC and two end caps. The projectile is attached to a fishing line contained in the reel mounted at the muzzle end of the barrel. The projectile has a loop mounted on one end made from a large paperclip. I drilled a couple of small holes in one endcap, fed the ends of the paperclip through and twisted them together internally before glueing the parts together. A fishing swivel is used between the projectile and fishing line to reduce the tendency of the fishing line to twist. Preliminary testing indicates that with 40 PSI it will easily clear a 100 foot tree.

Second Generation Shooter

Pictured above is my second generation Antenna Shooter. I removed the globe valve and substituted a Rainbird CPF-100 water sprinkler valve connected to two 9-volt batteries through two switches, a safety interlock switch and a push-button trigger switch. The two switches and 9V batteries are mounted in a Radio Shack project box underneath the sprinkler valve. To fire the launcher you have to lift the cover on the safety interlock switch and throw that switch before the trigger becomes active. Changing the design to the sprinkler valve resulted in 20-30 feet longer launches probably due to the valve opening faster. The original design also suffered from a tendency for the barrel to be jerked off target when you manually activated the globe valve, which is not seen with electrical activation of the sprinkler valve.

Third Generation Shooter

This is the third version of my Antenna Shooter. As you can see from the photographs I modified the second generation launcher by placing the barrel and air tank in parallel and connecting the two with a pair of Schedule 40 1-inch 90 degree elbows connected end-to-end for a 180 degree bend. They are connected using a piece of 1-inch PVC pipe. It was necessary to cut approximately 3/8ths of an inch off the smooth bore ends of both elbows to get the center-to-center spacing right on the two threaded ends. I had to turn the control box around 180 degrees as well to maintain the same switch orientation relative to the operator. I also rotated the fishing reel 90 degrees on the barrel from the second generation configuration. The best balance is obtained if the launcher is held with the air tank below the barrel and the fishing reel on top. In this configuration the trigger and interlock switches are on the bottom and conveniently located for firing with my right hand. I debated on whether or not to cut the barrel off even with the end of the air tank but decided to leave the barrel its original 24-inch length to increase accuracy. As a last step I added some cable ties around the barrel and air tank to tie them together securely and improve stability.

Fourth Generation Shooter

Pictured above is version four of my Antenna Shooter design. The major differences between generation three and four are as follows:
1) Triggering is now done mechanically, eliminating the need for periodic battery replacement.
I tapped into the top of the water sprinkler valve with a 1/4" NPT fitting and attached a blow gun and ball valve.
The ball valve acts as a safety interlock so the device can't be fired accidentally.
2) A bead of epoxy reinforces the joints around the pressure tank.
3) A 100 PSI pressure gauge has been added to the tank, eliminating the need for an external pressure gauge.



To build your own you will need the following parts:
1) 24 inches of 1-1/4" Schedule 40 PVC
2) 1 each 1-1/4" x 1" Bulkhead Adapter (threaded on the small end and smooth bore on the large end)
3) 3 each 1" close Nipples
4) 1 each 1" Sprinkler Valve (I recommend Rainbird CP-100)
5) 2 each 1" PVC 90 degree elbows (threaded on one end and smooth bore on the other)
6) 1 each 1" PVC schedule 40 pipe approximately 1-1/2" long
7) 1 each 1" x 2" PVC Bulkhead adapter (with the small end threaded)
8) 1 each 2" x 3" PVC Reducing Adapter
9) 1 each 3" Schedule 40 PVC pipe 12" long
10) 1 each 1-1/4" PVC Coupling
11) 1 each 3" PVC Schedule 40 end cap
12) 3 each 1/4" NPT close pipe nipples
13) 1 each 1/4" NPT ball valve
14) 1 each 1/4" NPT 90-degree elbow
15) 1 each blowgun valve
16) Epoxy putty
17) 5-minute epoxy
18) PVC Cement
19) PVC Primer
20) 1 each automotive Schrader Valve (the kind with a nut on the bottom end)
21) 1 each 1/8 NPT pressure gauge (McMaster-Carr p/n 38105K32)
22) 1 roll of Teflon Tape
23) 1/8" NPT thread tap (optional)
24) 1/4" NPT thread tap (optional)

I usually start assembly by building the air tank. The 1" X 2" Bulkhead Adapter fits into the small end of the 2" X 3" Reducing Adapter. It is not a flush fit so you may want to trim about a 1/4" off the end of the large end of the bulkhead adapter, although this is strictly cosmetic and optional. Be sure to use the PVC Primer and then apply glue to both the bulkhead adapter and the Reducing adapter. Fit the parts together with a slight twist to be sure the glue has all-over contact. At this point drill a hole in the angled shoulder of the 2" X 3" adapter (where it is thickest for support) to fit your Schrader valve. Attach the Schrader valve with the rubber washer and nut on the inside. Be sure to tighten the nut so that the seal is air tight. Next, glue the assembly to one end of the 3" PVC. Last step in the air tank assembly is to glue the 3" End Cap to the other end of the tank.

Once the air tank is complete take one of the 1" Close Nipples and apply a couple of layers of Teflon tape to the threads on each end. Thread one end into the end of the just completed Air Tank Assembly. The other end of the Close Nipple is attached to the input end of the Sprinkler Valve. Be sure flow arrow on the valve is pointed out of the tank. Thread another 1" Close Nipple into the output end of the Sprinkler Valve (Teflon tape is not required here).

Glue the short 1" PVC Pipe into the smooth ends of both 90 degree elbows, taking care to line up bot elbows so you form a perfect 180 degree bend or "Letter C" shape. Attach one end end of this assembly to the pipe nipple sticking out of the sprinkler valve output. Thread another 1" Close Nipple into the remaining end of the 180 degree bend.

Glue the 1-1/4" Coupling to one end of the 1-1/4" Schedule 40 PVC Pipe. Glue the 1" X 1-1/4" to the end of the 1-1/4" Coupling. This completes assemby of the Barrel.

Thread the small end of the Barrel Assembly onto the 1" Close Nipple attached to the other end of the 180 degree bend assembly. Depending on the particular brand of 90 degree elbows you purchase you may need a small wood block between the air tank and the barrel for support. I attach the wood block to the air tank with 5-minute epoxy. I deliberately do not glue the wood block to the barrel so it can be removed if necessary.

The next step is to drill a hole in the air tank for the pressure gauge. Use a bit slightly smaller than the threads on the pressure gauge. Be sure to drill the hole in the end of the air tank midway along the joint where the end cap attaches to the 3" PVC for maximum support. I prefer to tap the hole with a 1/8" NPT tap, but you can carefully thread a 1/8" nipple into the plastic to create the threads. Apply a couple of layers of teflon tape to the threads on the pressure gauge and thread it into the hole, making sure it is tight.

Unscrew the solenoid from the top of the sprinkler valve. Remove the screws holding the top of the sprinkler valve to the body. Cut off a piece of the epoxy putty and mix it until the color is uniform. Apply the epoxy putty to the hole in the top where the solenoid used to be. Let it dry. Now drill a hole in the center of the sprinkler valve top using a xx drill bit. I prefer to tap this hole with a 1/4" NPT tap, but you can carefully thread a 1/4" pipe nipple into the hole to create threads. Remove the pipe nipple and apply a small amount of 5-minute epoxy to the threads on one end. Thread this end into the hole in the sprinkler valve you just tapped. Let the epoxy set. When dry apply a couple of layers of teflon tape to the other end of the nipple and attach a 1/4" NPT elbow. Take another 1/4" NPT close nipple and apply a couple of layers of teflon tape to one end. Thread this end into the other end of the 90 degree elbow. Apply teflon tape to the other end of the close nipple. Thread the 1/4" NPT ball valve onto the remaining nipple end. Similarly attach another 1/4" Close Nipple to the other end of the ball Valve. Apply two layers of teflon tape to the other end of the close nipple and carefully attach the blow gun.