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.

Supplies

(4) aluminum soda cans

6 feet of RG-6 coaxial cable

24 inches of RG-59 coaxial cable

(4) F-type panel mounted CATV female solder connectors:

https://www.amazon.com/dp/B07W3K6JL7?ref=ppx_pop

(8) RG-59 coaxial connectors, the smaller the better

(4) right angle coaxial connectors:

https://www.amazon.com/dp/B09QLXDV2N?ref=ppx_pop&th=1

4-way cable TV splitter:

https://www.amazon.com/dp/B0077QMDGY?starsLeft=1&ref_=cm_sw_r_apan_dp_CNXMP328APYK19BH9VRY&th=1

Amcrest indoor camera wall mount, large L-bracket, or something similar

4" x 4" x 3/32" plexiglass

5¼" x 2½" x 3/8" acrylic block

3" x 7/8" x 3/8" acrylic block

(1) 3/8" x 3" bolt, washer, lockwasher, and nut

(2) 8-32 x 3/4" pan head screws & nuts

(2) 6-32 x 3/4" flat head screws

(2) 6-32 x 3/8" flat head screws

¼" heat shrink tubing

(4) stick-on rubber feet

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.

Step 5: Make the Connecting Cables

I used the older RG-59 coaxial cable for this step because it is smaller in diameter than the RG-6 and much more flexible. Even so, I still had to remove the outer cover to get it to bend enough to bridge the gap between the reflectors and the 4-way splitter.

Cut 4 lengths of cable that are longer than the distance between the antennas and splitter leaving enough to form S-shape loops which provide slack in case you have to pivot the antennas up or down on the mount. Then using a hobby knife, carefully slice the entire length of the cables and remove the outer covering only--leaving the copper braid intact. These particular lengths were 204mm for the lowers and about 157mm for the uppers, taking the 47mm length of the 90 degree connectors into account thus making each cable the same electrical length. This is important as the 4 signals will reach the combiner at the same time.

Strip the ends of each length and install a small RG-59 coax connector. These connectors are hard to come by anymore, but I scrounged up several from some old cables that I had. Instead of crimping the braids to the connector with a collar, I soldered them to the back side of the connectors and covered with a short length of heat-shrink tubing. Screw one end of each cable onto a reflector. Before connecting the other end, perform a continuity check between the coil and center conductor, and shield-to-reflector on each cable. You should have continuity on both, and open (no short) existing between the center conductor and shield.

Because 2 of the splitter inputs face the rear, I used two 90-degree connectors screwed together to form a U-shape on each input, so that the 2 upper cables can attach more easily. Once all cables are connected, lightly tighten them down with a 7/16" wrench.

Attach a stick-on rubber foot to each corner on the underside of the base to complete.

Step 6: Get It Working

Connect a length of coax cable from the CATV antenna input on a smart TV to the input of the 4-way splitter.

Download the RCA Signal Finder app to your phone and quickly setup by entering your zip code or current location, then select the networks you want to receive. The antenna is very directional and this app is helpful in aligning it to the television broadcast tower nearest your location. By placing the bottom of your phone flat against the front base of the antenna you can easily align it to the active broadcast towers shown in the app.

Once you have it properly aligned, set your smart TV to receive over the air channels and give it a few minutes to program.