HDTV Over-the-Air Antenna "Shrink Ray"

The Quad Tetrode "Shrink Ray!" HDTV Over-the-Air Antenna

Intro: The Quad Tetrode "Shrink Ray!" HDTV Over-the-Air Antenna

This is a variation of a simple, yet effective HDTV Over the Air (OTA) antenna that others have created and posted on internet sites. It's a table-top pumped-up version of the single-element type from those sites, and is good for receiving HDTV channels especially in deep-fringe reception areas. When my daughter first saw this, she aptly said, "It's a shrink ray!" Well the name stuck, and we added "Quad Tetrode" to it just for fun. It's also a quick backup for whenever the cable or satellite TV goes out (but that never happens, right?). Or if you want to eliminate those services and go over-the-air, then this antenna will work. I also found it useful for smaller bedroom TV's that don't have cable access.

STEP 1: Make the Reflectors

Begin with the empty soda cans. Using a utility knife, use caution and carefully cut off the entire bottom of the cans, about 1/2" up from the bottom. Then drill a 3/8" hole in the dead center of the bottom of each can, being careful as the aluminum is thin. Start with a few progressively larger pilot holes first before using the larger bit--a step-drill bit works well for this.

Insert a 3/8" bolt through the hole on the concave side and tightly secure with a washer, lock washer, and nut on the other side. Now insert the bolt into a drill press and while spinning on the lowest speed, gently press the can bottom onto a sheet of coarse sandpaper (I used 24 grit) to begin grinding away the aluminum bottom. This will leave a perfectly round parabolic shape when through. Repeat for the 3 remaining cans. Alternatively, you can grind off the can bottoms by hand using a circular motion on the sandpaper, but it will take a bit longer. You should now have 4 parabolic-shaped reflectors for the antenna.

STEP 2: Prep the Plexiglass Backing

On the 4" square piece of plexiglass, measure and divide it into 4 equal quadrants. In the center of each quadrant, slowly drill a 3/8" hole being careful not to crack the plexiglass. Again drill smaller pilot holes first to prevent damage. Each hole should be 1" in from each side and 2" between each other. Then drill a 1/4" hole in the center of the plexiglass for the camera mount to attach to it.

Insert the female coax connectors through the holes in each of the reflectors with the solder lug end facing outward, and then the threaded ends through the 4 holes in the plexiglass. Secure each connector with the nut on the back of the plexiglass, to hold the reflectors firmly against it.

STEP 3: Wind the Driven Elements

Cut the RG-6 coaxial cable into four 18" lengths. Using a hobby knife or a coax cable stripper, carefully remove the outer sheath, silver braid, and white inner core insulation, exposing the inner conductor wire. This is a copper-clad steel wire that is stiff and takes some effort to bend.

Using a 7/32" diameter rod or a #2 phillips screwdriver shaft in a vise, slowly wind 20 turns of the wire around the rod keeping the windings close together. Slide the coil off the rod and holding with pliers on each end, gently stretch the coil to 7 cm long. Straighten 3/8" of the wire in from each end of the coil, bend it inward toward the center, then straighten it even with the axis of the coil. Repeat this for the 3 remaining lengths of coax cable, making 4 coils total. Solder one end of each coil to the lug on the female coax connector on each reflector.

STEP 4: Mount the Remaining Parts

I employed an old Amcrest camera wall mount that I had as it was the right size and is adjustable. You can also use a large L-bracket for the mount. I also chose clear acrylic for the base and plexiglass for the antenna mount to give it an overall clean look, but you can use anything-- wood, plastic, etc. Be resourceful.

I attached the mount to the base a bit off center front-to-back and secured it with 8-32 screws and nuts, through holes in the base acrylic block. I then mounted the smaller block using 6-32 flat head screws, by drilling and tapping holes into the base. This bock serves as a riser for the 4-way splitter, which was screwed down on top of it by drilling and tapping holes in the riser block.