A 90 foot Irrigation Tubing Vertical
(click here to see some neat photos of antenna taken at sunrise: [sunrise 1] [sunrise 2] [sunrise 3] )
For the past couple of years I have been experimenting with making vertical antennas out of aluminum irrigation tubing. The most frequently asked question I get about this is: how do you raise the thing? I quickly ruled out such "solutions" as renting a crane, having an antenna raising party with a dozen people pulling on a dozen ropes, or building a conventional tower and using it to hoist up the tubing. What I eventually came up with was a 45 foot ginpole made of 4 inch tubing and a lot of ropes and pullies. The end result is that the vertical goes up or down in a few minutes with one person doing all the work on the ground. How this works is summarized in this [diagram] . The finished vertical is 90 feet, consisting of two 30 foot pieces of four inch tubing and one 30 foot piece of two inch tubing, stacked with the small tubing on the top. photo: [looking west] . The heavier ropes seen on the left are the raising ropes. The other ropes are guy ropes. Four sets of guys (north, south, east and west) are used at each level (15, 30, 45, 60, and 90 ft). When the antenna is up, the ginpole is normally laying on the ground. photo: [looking west] [looking east] . The antenna and ginpole are mounted on side by side pivots at ground level, about a foot apart. The raising ropes go from the top of the ginpole to the 30 and 60 foot points on the antenna.
The raising procedure starts with the ginpole vertical and the antenna laying down. photo: [on ground] . For later reference, note that this view is looking east. (The way the ginpole itself is raised initially is to simply walk it up "Iwo Jima" style. 45 feet with ropes hanging off the top is about the limiting height for me, and if I were stronger, I would start to worry about bending the tubing at greater heights). To the right of the ginpole, ropes come off the end of it to the 30 and 60 foot points on the vertical. To the left, there appear to be two ropes as well, but this is actually a single rope going through a pulley mounted at the end of the ginpole. The lower end of it goes to a pulley on the ground mounted 45 ft from the pivot. The top end goes to a fixed anchor about 120 ft from the pivot. After passing through the ground mounted pulley, the rope runs along the ground to the right for about 150 feet. The ginpole has side guys from the top to 60 feet from the pivot running east and west. All east and west guys for the antenna are preinstalled and tightened on the ground. The south guys are measured and preinstalled on the ground but of course are not under tension at this time. The north guys are preattached at the antenna and tied off loosely to the east or west guy point, as if they were west guys, just to keep them from dragging on the ground, dangling, etc. Guy points are 30, 60 and 90 feet from the pivot. photos: guys close up .
To start raising, the rope going off to the right is pulled. This takes in line through the ground mounted pulley 45 feet north of center which pulls on the top pulley of the ginpole. This causes the other rope going to the left to tighten and help pull the ginpole to the left. The top rope being tied off to a point at 120 feet, has much better leverage than the rope coming from the pulley at only 45 feet. Together, there is a 2:1 reduction in force needed, reducing the rope pull to about 30 lbs. The next six photos show the antenna raising and the ginpole lowering as the rig slowly goes up. photos: [raising 1] [raising2] [raising 3] [raising 4] [raising 5] [raising 6] [raising 7] [raising 8] . The pull rope has handles every 30 feet that I can hook over a post to stop the process at any point to do visual checks (or take photos). The rope is long enough that I do not stand within a 90 foot radius of the antenna when it is being raised. If anything is going to go wrong with this antenna, it will probably be when raising/lowering. During raising, the top 30 foot section does bend somewhat, but not to where it takes a permanent set. In the last photo, the weight of the ginpole and antenna just about counterbalance each other. If I continue to pull the rope after this, the ginpole will start to fall on its own and pull the antenna upright. Since I am standing to the right, I can grab the 60 foot south guy rope to gently let it down. The lowering proceedure is basically the reverse of the above.
The base is basically a 4x4 sunk into the ground with a double wooden yoke holding carriage bolts which pass through the bottoms of the poles as pivots. photo: base . More specifically, the 4x4 is goes into the ground about 30 inches and has a "foot" consisting of a 16 inch wide by 2 inch thick concrete flagstone bolted to the bottom. It is also "guyed" on the north and south sides by underground guy wires. Each guy wire is anchored by a "deadman" consisting of a similar flagstone buried 30 inches. This prevents the 4x4 from being pushed sideways when raising/lowering the antenna. The bottom of the irrigation tubing fits inside a short piece of 4 inch PVC pipe which is slotted and clamped to the tubing with hose clamps. The PVC pipe in turn is inserted into a "slip to male iron pipe thread" adapter. This adapter has a smaller inside diameter than the tubing thus providing a shelf for it to rest on. A hole is drilled through the threaded part of the adapter for the carriage bolt to pass through (the iron pipe threads are superfluous for this application).
The 30 foot pieces of tubing are connected with insulated joints. For the 4-inch to 4-inch joints, the tubing is butted together with a spacer sandwiched in between. The spacer consists of a PVC "3-inch" coupling (for 3-inch pipe) which coincidentally has an outside diameter of exactly 4 inches like the tubing. photo: lower joint The sandwich is clamped with a short piece of 4 inch PVC tubing that is slit lengthwise, wedged open slightly and slipped over the joint centered on the 3-inch coupling. The center of the 4 inch PVC is squeezed shut by a hose clamp. The ends of it are squeezed shut by slipping 4 inch PVC couplings over the ends. Originally, hose clamps were used for this purpose but were found not to be strong enough. The other side of the couplings (that is not holding the 4-inch PVC pipe) has a 1/4 inch gap between it and the irrigation tubing. The coupling is has 1/4 inch holes drilled into it, into which small (3/4 inch) U-bolts are inserted. The U-bolts are held with 1/4 inch nuts on both the inside and outside of the coupling. There are 4 U-bolts at 90 degree angles around the coupling which are used as guy attachment points. The 3/16 inch dacron guy rope is looped through the U-bolts and protected by a 1/8 inch thimble. The undersized thimble allows the rope to be pressed into it and held, due to it being slightly undersized. A figure-8 knot is used to make the loop. Two holes are drilled in the 4-inch PVC pipe in the center and 1/4 inch by 2 inch stainless bolts protrude through this hole. The bolts pass through holes about 1/2 inch from the ends of the tubing and are secure by nuts on the inside of the tubing. The bolts are used to get electrical connections to the tubing.
The 4-inch to 2-inch joint is also insulated, but a different construction is necessary to transition the size. photos: upper joint upper joint (another view) In this case, again a "3-inch" coupling is again used, which is clamped simultaneously along with the tubing by a 4 inch PVC pipe as before. In both ends of the coupling a "3-inch spigot to 2-inch slip" adapter is inserted. 2-inch PVC pipe is inserted through both of these adapters. It is necessary to sand off the lip that the pipe normally bottoms on. The 2-inch PVC pipe has an inside diameter slightly larger than 2 inches but after slitting and clamping with hose clamps it can easily grip the 2 inch irrigation tubing.
Also seen in the photo , just below the 4 inch to 2 inch insulated joint is a guy attachment collar. This is a 4-inch PVC coupling drilled for U-bolts as previously described. It rests on/around a short piece of 4 inch PVC pipe that has been slit lengthwise and clamped with hose clamps around the tubing. This same technique is used at 15 and 45 feet for guy attachment.
The insulated joints have an electrical circuitry box consisting of a PVC "condulet" at the 30 foot photo and 60 foot photo points. (In the 60 foot photo, you can also see the grid wires of the ground screen: 16 gauge tinned copper in a 3 by 3 foot grid with the crossovers soldered.) The condulet boxes contain relays to effectively change the height of the vertical to 30 feet for 40 meters, 60 feet for 30 and 80 meters, and 90 feet for 160 meters. Ferrite rod inductive chokes are used to get DC past the open relays at the lower level to get to the upper level. These chokes also tune out the gap capacitance, which is on the order of 2 pF. Control wires for these relays are spiralled around the tubing every 3 feet so they don't slap in the wind and make noise. A treatise on electrical design is now under construction.
The antenna is fed with 1000 feet of open wire line. A photo shows the line as it approaches the antenna, also a close up photo of line. The matching transformer consists of a stack of 3 toroids of 2.4 inch diameter followed by a coaxial/toroidal balun. A description of the open wire line is now under construction, mostly photos so far.