Antenna Cannon For Amateur Radio

As an amateur radio enthusiast, [Andrew] sometimes has to set up impromptu antennas up to 160 meters in length. The easiest way to get these antennas off the ground is to drape them over trees, a feat normally accomplished by lofting fishing line into the air with a slingshot or bow and arrow. [Andrew] thought slings were so last century, so he came up with a spud gun inspired antenna launcher.

The launcher is built out of PVC and launches a foam filled tennis ball that can reel out 150 yards of Spectra line. In a moment of brilliance, [Andrew] decided to add an augmented reality HUD. The display is actually [Andrew]’s phone running an app called Geocam that provides him with a display of elevation and azimuth overlaid on the phone’s camera feed. The results of [Andrew]’s build are fairly impressive. The cannon was able to lob a tennis ball over a 110 foot tree at half the pressure rating of the PVC. The grouping was pretty tight as well, more than sufficient to run a line over a tree.

[Andrew]’s antenna cannon is an awesome piece of work and unlike most french fry cutters, it’s a useful tool. If you’re interested in seeing 160 meter antennas heaved over the tops of trees, amateur radio field day is next month week, June 25th and 26th.

32 thoughts on “Antenna Cannon For Amateur Radio

  1. How many times do we have to repeat this before people understand?

    PVC IS NOT FOR COMPRESSED AIR. Says so, right on the side of the pipe in capital letters. The pressure rating is for WATER.

    It doesn’t say “LOLZ J/K IF YOU’RE AT HALF THE PRESSURE RATING.” Every time you build a potato/t-shirt/antenna/dildo canon using compressed air and PVC, Baby Jesus cries.

    1. Yo Doppy!
      Every study any physics at all?
      Here are some of the differences between air and water pressure: Water is much heavier than air. A cubic foot of air weighs 1/12 pound. A cubic foot of fresh water weighs 62.4 pounds and a cubic foot of sea water weighs 64 pounds. Air is a mixture of gases, principally oxygen (O2, 21 percent of the air by volume) and nitrogen (N2, 78 percent by volume). Each gas exerts its own independent pressure, the sum of which equals the total air pressure (Dalton’s law). Unlike water, air (and any other gas or mixture of gases) is compressible; the greater the pressure exerted, the more tightly packed together are the individual gas molecules. Regardless of the air pressure, however, water molecules are much more tightly packed together than air molecules. Compared to air at sea level pressure (1 atm.), water is about 800 times denser. Just as air has weight and exerts pressure on all sides of an object in the atmosphere, water exerts pressure around any object immersed in it. We can push water out of the way because its weight is distributed on all sides and the molecules can be easily moved. The resistance we feel under water reflects the extreme density of water (compared to air), and the fact that it takes time for water molecules to move out of the way. Water pressure, like air pressure, is a function of weight; the deeper one goes the greater the surrounding water pressure.
      In short the warning on PVC pipe tyhat it’s not for Air pressure is a disclaimer by the manufacturer to protect themselves from any legal liability. Hence the label warning. Personally I use HDPVC Air pipe use in pheunmatic piping in factories. It’s actually cheaper and you can find it surplus on line. Many type of “Plastic” Pipe can even carrry presurized steam. there is a guy on YouTube who made a 12 cylinder steam powered engine out of HD PVC.
      the only metal used were the bearings and the bolts in most cases. If you use just standard OTC PVC pipe for your Air storage bladder or canister. You can just put several layers of the Packing with strings in it or a good quality duct tape. I also put in a Blow off valve set at 65 PSI. At 65 PSI the valve opens to let out any excess gas.

  2. quick question — How accurate in spooling out exact lengths is this device? Does the reel have a measurement device that can tell you exactly what freq. the longwire is optimized for at any particular moment? If not, I say that that would be an obvious improvement…

  3. @ Brian – Noted and corrected.

    @ asheets – the cannon only spools out a leader which is then tied to the antenna. I’m not sure about the weight per foot of copper wire, but I don’t 80 meters of copper would be launched very far.

  4. He didn’t design the antenna launcher, but he probably built it, it’s available as plans (free), a kit, or fully assembled. I believe the one above is the CSV19, I have the same one, only it’s painted camo. Check out more about it here I would be more interested in the augmented reality portion of this. The compass is a really nice feature for aiming dipoles (N/S, E/W). I don’t use my antenna launcher that often, but I think it would be neat to code an app to calculate range, height, and angle (touch screen to select point), and recommend the required PSI to accomplish the task (doesn’t have to be exact). This thing can shoot tennis balls a lot further than you’d expect. Using it 2 or 3 times a year, one quickly forgets just how far the ball will actually go with 80 PSI in the tank. Totally impractical waste of time to write such an app, you bet, but it would still be cool. Great job Andrew (REALLY like the steampunk look). Good luck with Field Day.

  5. Why do people continue to make compressed air based PVC cannons? Stop using PVC pipe with compressed air. Go aluminum if you care about weight. Yes, the cost will be higher but you make guns out of steel, titanium, alloys because it is a gun. It produces compressed gas and it needs something that can handle the forces created.

    I know that this doesn’t generate the forces on the same level as a firearm but my point is that when you make a product, you need to properly engineer the materials that go into it. PVC is an inappropriate material to use. Can you get away with it, possibly for a long time? Probably. Should you? I can’t answer that for you specifically but my opinion is no.

    I know PVC is cheap and “rated” for 120 – 200 PSI but that assumes brand new pipe without cracks, scratches and the fail mode of PVC doesn’t change if you have compressed air in it vs water. Lots of things are cheap but are otherwise a very bad idea to use.

    Please stop using PVC in compressed air applications.

  6. I’m not going to deny that there is a hazard with Using PVC in these applications, but I don’t see people moving away from using it anytime soon. My guess if we see something featured that use welded aluminum, Someone with pop off with; unless the welder was a certified welder is could be dangerous. And welding AFIK is the only economical way to use aluminum pipe. They would be wrong, but we have to deal with probabilities.
    Away here in Kansas we need portable tree. In the event the hack a day folks run across home shop built portable masts, I’d appreciate there being posted. Good luck on Field Day

  7. Well, another launcher, this one still not 100% safe but at least it’s not the worst we’ve seen on here yet.

    The drilled/tapped holes are in double-wall PVC which is spot-on.

    Two big problems safety-wise I see: The lack of a pressure relief valve.. (a CYA part), and the use of non-pressure-rated PVC fittings on the pressure chamber (the reducing coupler).

    The HUD is a really nice touch but honestly not needed if you know what you’re doing. Might make things a tad easier I suppose.

    Steampunk theme – bonus points.

  8. @willow It does have a pressure relief valve, it’s on the other side of the barrel, I think it’s set to 120psi or so.

    @SubPar Well, it COULD be, but it’s rare. I have a full wave 160m loop, that’s about 560 feet of wire. But I agree, I thought the same thing as you when I read that.

  9. @KC2PHO: Apologies, didn’t see it from the photos.

    Only thing I would note to the builder, or anyone looking to do this, is that the blow-off rating should be close to your maximum operating pressure, and not close to the maximum pipe rating.

    In this case he marked the MOP at 80psig, so the BOV should be closer to 90psig. Generally speaking the maximum rating on 4″ sch40 is 130psi, and that’s a best-case scenario at a specific temperature (70*-72* usually).

    It drops as temperature rises, and as temperature falls PVC becomes brittle and prone to sudden fissure cracking and bursting, most especially if it takes an impact of some sort.

    Which is another reason why the 4->2 reducer on the pressure chamber should be pressure-rated instead of DWV rated.

    Still loving the steampunk theme, a lot!

  10. One other note for anyone interested, don’t use epoxy to fill the solenoid cavity. Over time it will begin leaking due to stress and temperature shifts.

    Instead what I find handy for 1″ valves is to get a threaded PVC plug, either the inverted kind or the normal, which fits the threads of the cavity. Usually a 1″ plug will work, sometimes 3/4″ has to be used.

    Then grab a gasket, honestly a garden hose gasket works perfectly. Put a little bit of silicone grease on the top side (where the gasket will touch the plug) so it doesn’t become distored when threading it in place.

    It’s a 1 minute job, provides a perfect seal and is servicable if needed. Also no need to wait 24 hours for epoxy to set.

    This is the style plug I’m referring to:

  11. I am pleasantly surprised by this post and it’s comments. A pneumatic launcher that is (finally) pneumatically actuated (although still uses a sprinkler valve). I don’t even have to say anything about using DWV fittings because someone already said it, yay!

  12. @willow Good stuff to know, I’ll be re-engineering mine soon. Actually, now that I look hard at the photo, I don’t even see the BOV, perhaps he didn’t install it. I do know that it’s adjustable, I’ll have to properly set mine if it’s not at 90.

    Trust me, those couplers aren’t pressure rated. I, like an idiot, put something in the barrel which shouldn’t have been there (trying to be funny) and the coupler failed at 60 psi, right against my chest. Didn’t hurt, wasn’t injured (VERY lucky), but I did have to change my pants. Lets just say I respect it much more than I did before.

    I think PVC is okay, provided you take real good care of it, keep it out of the sun, heat, and cold, and replace EVERYTHING after a few years. I would like to see some kind of ‘safe’ fail point on these things though.

    While building mine, I was really nervous about the safety of this thing. The pressure vessel is held together with pvc cement, the valve, gauge, and PR valve are threaded into the pipe, the sprinkler valve is rigged with epoxy, and the entire thing seems fragile. Needless to say, I don’t get that warm and fuzzy feeling of safety when using it. But it’s still the most safe, fun, and unique way to get a rope in a tree.

  13. Just wanted to mention that all of the components in the launcher are in fact made out of pressure rated PVC. There are two types of PVC pipe/fittings – pressure rated Schedule 40 and “Foam core PVC” used for DWV (which must not be used for such application). The 4″ pipe (used for the pressure tank) was clearly marked as “max 220 psi” with red ink on the side. After the launcher was built, it was wrapped in a heavy blanket and pumped to ~110 PSI (100 PSI is the max of the pressure gauge and I did not want to damage it with much higher pressure)for about 30 min. Then I subjected the launcher to a mild shock (droping if from a little over a foot onto concrete floor as it was still wrapped in the blanket). That was my safety test. Is it 100% safe – most probably not! but again – anything that launches a projectile with compressed air is less than 100% safe. Building and using such device requires good judgement and caution.

  14. Andrey,

    You have no idea what you’re talking about. Schedule 40 pipe is WATER pressure rated.

    WATER does not compress. Air does. When you fill a PVC pipe with water, if the pipe cracks/breaks, then water goes everywhere, but that’s it.

    When you fill a PVC pipe with air, if the pipe cracks, the compressed air provides considerable stored energy and will force the pipe (which doesn’t simply break but shatters like glass) apart.

    Those OSHA reports include photos of maimed body parts, in some cases belonging to people who were in some cases on the other side of a piece of DRYWALL from the pipe that shattered.

    Charging the device with air near others is extremely irresponsible. Even transporting it in your car is dangerous- if it let go, the flying glass could seriously injure or kill people. Stop screwing around!

  15. Not to start a pointless argument here but Pounds-per-square-inch (PSI) is a unit that represents force applied to a specific surface area and it makes no difference if the force is excreted by liquid, gas or solid object. IF the pipe fails – yes – it is a different story – shrapnels are propelled at higher velocity by the gas – same holds true when a gun barrel fails – and they too fail sometimes. That’s why there is a max pressure limit. It is a common sense that you dont drive around with a loaded PVC compressed air tank – just as you dont drive around with a loaded shotgun in the back of your car. As for OSHA recommendations – they are for safe WORK ENVINRONMENT not for back-yard experiments. Is it dangerous? – yes – is soldering without safety goggles dangerous – yes to that one too! Should you use it around the local playground – NO. There is an equal amount of danger from the projectile (weighted tennis ball) traveling at 100 miles/hour. Just as using a sling-shot or bow and arrow and even climbing a tree to put the antenna wire, someone can get hurt due to lack of common sense. FYI – I did not invent the concept of pneumatic PVC spud gun – thousands of these are built all over the world – my contribution is the idea of using Android Phone as Augmented Reality Scope, showing the angle of the barrel for more precise aiming – that’s all. If I was really paranoid, i’d stay home and play chess instead of installing an antenna or repairing the 8kV power supply in my RF amplifier. Here is an idea for those who are really paranoid – a few layers of ballistic nylon from a backpack or kevlar fabric around the compressed air tank and valve wrapped with ballistic nylon straps should ease your squint.

    1. I believe the difference is heat. Gasses heat up when pressurized, which can cause the PVC to fail prematurely. Or something like that.

      But who am I? Just another amateur…

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