The Gray-Hoverman homebuilt TV antenna can be assembled from common plastic plumbing pipe and fittings. Here are some tips compiled from my build of a GH6 antenna having straight NARODs, but these hints can be useful no matter which of the many variations you build. The color pdf drawing I used to build my antenna may be found at this link http://www.user.dccnet.com/jonleblanc/Canada_TV_Stations/Gray-Hoverman/DBGH_VHF_hi_Antenna.pdf. Note the license information printed on the drawing, which is offered free for private use, but commercial exploitation is prohibited.
This is one of several of my Instructables related to building this antenna. To see the others and my related Instructables, click on unclesam in the INFO box at right and repeatedly click NEXT to page through them all. To receive automatic notice about my future antenna construction postings, you can click in the INFO box to subscribe to me. In the final step I include links within Digitalhome.ca that further describe the antenna. At the end I have edited in an assembly photo of the spine for a GH10n3 antenna I subsequently built.
Step 1: The Sharpie Sled
Holes need to be drilled in lengths of PVC pipe that are precisely placed in spacing and perpendicularily, and marking the pipes lengthwise on four quadrants makes that easier. This is best done after a piece of pipe has been cut to length. The pipe is clamped to a flat surface in several places, so that the pipe is in contact with the surface along its entire length. A fine-point marker fastened to a wood block is carefully drawn along the length of the pipe. Locations of the remaining quadrants may be marked using a circle-drawing template. The pipe is then rotated and clamped in position so the marker's point will follow each of the remaining quadrant marks in turn along the pipe's length.
Step 2: Mark Pipe Quadrants Without a Circle Template
The remaining quadrants can also be marked using a narrow strip of paper after one line has been made along a pipe using the Sharpie Sled. With one end of the strip set to the line, wrap the paper to overlap, then mark the point of overlap. This creates a strip of paper whose length is the circumference of the pipe. Fold just the circumference in half and crease it, then fold that in half and crease it, then mark the three resultant folds. These and the original mark divide the circumference equally into four parts. Wrap the paper around the pipe with the original end against the line again, secure it with a rubber band, and transfer the remaining quadrant marks to the pipe. Do the same at the other end of the pipe then connect the dots using a straightedge.
Step 3: Mark CPVC Pipe
I used some half-inch CPVC pipe in my antenna, and it needs to be marked lengthwise on opposite sides so it can be drilled and secured into the antenna with the proper rotational alignment. The mold marks on two CPVC tees can be used to accurately mark lines along the pipe on opposite sides. The mold marks on the tees are enhanced with scribe or marker. The tees are placed on the ends of the pipe and their bases pushed onto a flat surface to align them in the same rotational position. The mold marks are transferred onto the pipe on opposite sides, then the dots are connected using a straightedge.
Step 4: Mark PVC Fittings for Drilling
PVC fittings need to be drilled in precise locations. Their mold marks (enhanced in the photos with pencil) locate their centers in one axis, and the mold marks of two identical fittings can be used to find the center of a tee in the other axis. The center is punched to help start a drill, or if the hole needs to be offset from the center, the offset is measured and that spot punched. I mark the spot on both sides of a fitting and drill both sides, rather than drill through from one side. Two tees can be clamped so that a straightedge can mark the center of the middle tee in its other axis, and the same can be done to mark the center of a cross fitting. A forstner bit is stiff and has a sharp point, so it will start in the punch mark without wandering on the curved surface.
Step 5: Mark CPVC Fittings
Half-inch CPVC fittings can have their centerlines marked for drilling or as an aid to alignment during antenna assembly. The fittings have tapered bells, so provision needs to be made to keep them level for marking. A temporary arrangement of other fittings can be assembled to keep the fitting from rocking, and fittings can be added to the outboard fittings to also keep them from rotating. The mold marks of the outboard fittings (enhanced in the photo with pencil) can be used to mark the other axis of the fitting in the middle. The centerline of the top of the tee can be marked in a similar way using only the two outboard tees connected by short pipes. The bottom edges of the two bells of the two outboard tees are pressed onto a flat horizontal surface, to align the two together rotationally, and the bell of the middle tee pressed against a vertical surface perpendicular to the horizontal surface. A straightedge can be used to mark a line along the top of the tee.
Step 6: Drill Pipe
Once the pipe is lined along its quadrant axes, the locations of the holes to be drilled are measured and marked with a center punch, on both sides, so each of the thru holes can be drilled from both sides. Using my method for assembling the antenna, the hole locations are measured from the lengthwise middle of the pipe, then outward toward both ends. I use a drill press having a moveable vise. I select two hardwood or metal rods having exactly the same diameter to cradle the pipe, rather than squeeze it with the vise. The rods allows me to make all the holes exactly on the diameter of the pipe without having to repeatedly adjust the front-to-back location of the pipe under the drill's quill. Once the quill is exactly centered between the jaws of the vise, a tube set onto the dowels can be positioned by sliding it lengthwise and rotating it so the hole's punch mark meets the point of the drill bit. The vise is first centered front-to-back under the drill's quill by chucking a precision circular object in it, such as a large forstner bit. The vise is adjusted toward the user until its fixed back jaw touches the bit. The moveable jaw is then adjusted until it touches the bit. The bit is withdrawn and removed from the chuck. Neither the vise's position nor that of its moveable jaw should be moved until all the holes are drilled. With the drill turned off, the sharp point of a forstner bit is best for finding a punch mark as the pipe is slid and rotated under it. Once found, the quill is locked down and a hold-down is used to secure the pipe. The drill is turned on, the quill is unlocked and the hole drilled. Not shown is a shop vac nozzle that is positioned to catch the chips.
Step 7: Let's Stick Together
Plastic pipe and fittings are assembled by first priming and then cementing them using only products sold specifically for that purpose. An all-purpose cement will work for PVC and CPVC, and the resultant joint will be as strong as if the two pieces were manufactured as one. The photo shows a test of my method for cementing a half-inch CPVC pipe through a PVC pipe. The CPVC was pushed in to almost its final position, then cement was dabbed on the CPVC using a Q-tip, only on the part outside the PVC. The CPVC pipe was rotated and pushed in about a quarter inch, then cement dabbed on the protruding short end of the CPVC, only outside the PVC, and the CPVC pipe drawn back, while being rotated, to its intended eventual location and rotational position. The joint was left alone overnight then was subjected to a straight pull test of 75 pounds for 24 hours, then gripped with pliers and twisted with all the massive upper body strength of a retired engineer. The joint showed no hint of failure or even weakening.During final assembly of the CPVC pipe parts into the PVC parts, the parts are tried dry and measurements made, then marked, or spacers used, to ensure that the antenna's elements will be cemented in place with the correct spacings and rotational orientations.
Step 8: Attach 1-1/4 Inch Pipe to 1-inch Tee
My antenna attaches to a mast of 1-1/4 inch diameter, which is a snug sliding fit inside a 1-inch PVC "cross" fitting. I used 1-inch fittings and short pipe tubes for the remainder, but wanted to use 1-1/4-inch PVC pipe for the antenna's vertical spine. I found a way to join the spine directly to a 1-inch tee without need for two additional adapters. The inside diameter of 1-1/4-inch pipe is only 30 thousandths of an inch larger than the outside diameter of 1-inch pipe. I drilled four 3/8-inch diameter holes one and one quarter inch from each end of the 1-1/4 inch pipe, then slit the pipe from the ends to meet the holes. Gentle pressure from two hose clamps is enough to snug the pipe onto a 3-inch long section of 1-inch pipe, with a jig used to set the proper length and rotational alignment during cementing.
Step 9: Active Element and Straight NAROD Holders
I formed holders for the ends of the antenna's active elements, which I made from 1/4-inch copper tubing, and the straight #10 copper wire NARODs, using 1/2-inch CPVC pipe and modified "bracket" 90-degree elbows. These elbows were chosen because they have a square bend, and the brackets were sawed off. I first used the mold seams on a different style elbow to mark the centerline on both sides of each bracket elbow for later drilling a hole to run the NAROD through. I then cemented a length of CPVC pipe into the elbow and made two saw cuts on the bandsaw. Sawing created a flat for bolting the end of my active element to, just the right distance below the NAROD's support hole (hole not shown).
Step 10: Tophat NAROD Holder
I designed my antenna with a straight NAROD, but built in provision for trying out the several shapes and sizes of tophat NARODs. The photo shows how a 90-degree standard elbow can be drilled through to make an adjustable holder. It can be slid up and down and back and forth, then cemented in place to accommodate any tophat. A modified pipe cap confines the tophat, simulated in the photo by a short length of copper tubing.
Step 11: Antenna Information Links
1. Introduction to the Gray-Hoverman antenna
2. Antenna Research and Development Forum
3. Link to the license:
Step 12: Plastic Spine for GH10n3 Antenna
Following the SBGH6, I built a GH10n3 antenna that has high gain for VHF-high and UHF channels. The photo shows the stages of assembly for the spine. This antenna worked very well.