The Gray-Hoverman homebuilt tv antenna requires a number of reflector rods of particular lengths, some made of two rods separated by a precise gap, others of one continuous rod. The reflector assemblies are not of the same length, and they must be installed in the appropriate locations in the antenna. I made mine from hollow rods scavenged from neighbors' defunct commercial antennas and developed my own way to attach them to my Gray-Hoverman. A second method used in a second antenna follows the first, and may be easier for most folks to build. 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.
Step 1: Tools and Materials
Metal tubing, aluminum, three-eighths inch diameter (nominal), the amount depending upon the antenna version being built. Tubing scavenged from old tv antennas will have an open seam lengthwise.
PEX plastic plumbing tubing, three-eighths inch size, one five-inch long piece for each reflector assembly (eight for the example antenna)
CPVC plastic plumbing tubing, one-half inch size, one five-inch long piece for each reflector assembly (eight for the example antenna)
wood block, twelve inch length of two by four (actual 1 and one-half by three and one-half inches)
Flaring tool for flaring copper tubing
Hack saw, miniature
hex nut, metal, that will fit loosely over the metal rod
file, metal, for deburring cut tubing
Drill press or electric drill, bits of five-eighths (0.625) inch diameter and one-half inch (0.50) diameter for making the slitting fixture
Electric drill, portable, bits of 3-eighths inch (0.375) diameter, 25-sixty-fourths inch (0.390) diameter, and 13-thirty-seconths inch (0.406) diameter, for reaming PEX tubing
Band saw with wood blade (a hand hack saw will work)
Step 2: Totally Tubular
I scavenged lightweight aluminum metal tubes from old antennas, which is usually three-eighths inch outside diameter. A flaring tool made for use on copper tubing provides a solid grip on the aluminum tubing without damaging it while a miniature hacksaw cuts cleanly. A large metal hex nut slipped over the tubing spaces the saw's frame off the flaring tool and provides a surface that the blade can be pressed against for making a straight square cut.
I cut the metal rods to this color downloadable pdf plan, though there are many variations of the Gray-Hoverman antenna design. The plan shows the sizes and spatial relationships of the antenna's parts, but not how to build it. My design has the reflector rods stuck through a vertical spine consisting of one and one-quarter inch diameter schedule 40 PVC plastic pipe. Note the licensing restriction on the drawing itself. http://www.user.dccnet.com/jonleblanc/Canada_TV_Stations/Gray-Hoverman/DBGH_VHF_hi_Antenna.pdf
Step 3: Make the Slitting Fixture
The five-inch CPVC tubing and PEX pieces will need to be slit. A simple fixture will hold them while they are being cut lengthwise by a saw. Do not slit the PEX until it has been reamed inside to fit over the aluminum tubing. Drill a one-half inch diameter hole through (or as deep as possible) from one edge of the 2 X 4, its center one inch from the end of the wood block. Drill a five-eighths inch diameter hole through (or as deep as possible) from the same edge of the 2 X 4, whose center is one inch farther from the end of the block than the center of the other hole. Saw a vertical slot, through the centerlines of the holes, until it intersects the larger hole.
To slit a section of plastic tubing, insert it all the way into the appropriate hole, use the fixture to push it into the saw blade. If a band saw is not available, a hand hack saw could be used to make the slot in the fixture and to slit the tubing.
Step 4: Ream the PEX
The six reflectors associated with the antenna's zigzag active receiving elements consist of two pieces of metal rod separated by an air space between their ends. The two reflectors associated with the two straight NARODS (passive elements that allow the antenna to also receive high-end VHF stations) are of one continuous piece of metal tube each. Cut a 5-inch length of PEX and CPVC tubing for each reflector assembly, eight total of each for the example antenna.
Use an electric drill and bits to ream out the inside of the PEX (not yet slit lengthwise) until the aluminum rod will be a tight fit inside. The rods from different scrounged antennas will not be exactly the same diameter. Start reaming using a three-eighths inch diameter bit and work up in size if needed. It is not necessary to actually be able to push the antenna rod into the PEX until it is later slit. Ream only little more than half the length of the PEX, then switch ends.
Step 5: Taper the Ends and Slit the Plastic Tubing
Sand or file the ends of each piece of PEX and CPVC into a taper. This will make it easier for the PEX to slip inside the CPVC and for the CPVC to later be forced into its 0.625 inch diameter mounting holes in the antenna's PVC spine. The nominal outside diameter of the half-inch CPVC is 0.625 inch diameter. With it slit and stuffed with the slit PEX and the antenna rod, insertion into its mounting holes will squeeze the CPVC, which will in turn squeeze the slit PEX, which will grip the metal rod tightly.
Slit the lengths of PEX and CPVC plastic tubing lengthwise.
Step 6: Measure and Mark
For the one-piece NAROD reflectors, mark the exact center of the rod and the center of the piece of PEX. Use them to mark the metal rod just outside the ends of the PEX so it will be possible to confirm that the rod is centered once inserted.
For the two-piece reflectors, use a block of the width specified for the gap between the two rods, and its center marked. Align the block with the center of the PEX and mark the rods just outside the ends of the PEX. It is a good idea to mark the center of the CPVC as well and mark on both sides of its center so it will be possible to confirm that it is centered in the antenna's PVC spine tube when it is eventually installed. The spacing of these marks will depend on the diameter of the antenna's spine tube.
Step 7: Slip and Slide
Slip the PEX over the rod (or the two rods) to the marks on the rods, with the slit in the PEX aligned with the seam in the rod. Gripping the rod in the flaring tool will make it easier to slide the PEX over the rod. Next, slip a slit length of CPVC completely over the PEX, with the slit in the CPVC aligned with the slit in the PEX. Gripping the metal rod in the flaring tool, with one end of the PEX against the face of the tool to keep the PEX from sliding along the rod, will make it easier to slide the CPVC over the PEX. Once the CPVC is started over the PEX, it may need to be pushed using another piece of CPVC that is longer than half of the longest reflector rod, even using a hammer to tap it into its final position against the flaring tool's face. Verify by their marks that the rods are properly situated in the final assembly.
Repeat to make the eight reflector assemblies. Note that the reflectors are not of the same length and that they must be installed in the appropriate locations in the antenna. Note also that PEX is easily damaged by ultraviolet light. If the antenna is to be mounted outside, drill a 3/8-inch diameter hole through the end of 1/2-inch CPVC pipe caps and cement them on the ends of the CPVC pipes once the rods are installed in the antenna.
Step 9: Second Method for Reflector Rods
I used a tubing flaring tool to flare the inner ends of each tube, until it was a sliding fit inside a half-inch plastic pipe. A short length of smaller diameter pipe, such as PEX, split lengthwise, defines the gap between the two pieces of aluminum tube. An aluminum pop rivet is installed in each tube, so that it extends past the end of the half-inch plastic pipe. The plastic pipe cap presses against the pop rivet, which keeps the tube from pulling out. The tubes are marked so that the mark on one can be kept in its proper location while the other cap is cemented in place. The half-inch pipe is also marked to indicate when it is centered within the spine. The second cap is cemented in place once the assembly has been cemented into the spine of the antenna. Weep holes are drilled in the bottoms of the sides of the caps.