Intro: Scratchbuilt Wooden Offset Satellite Dish
I had come across some websites where several people built their own prime focus satellite dishes, one Australian man even built a huge 13 metre offset dish. What is the difference? Prime focus is what you think of when someone says 'satellite dish', offset is what you see mounted on the side of someone's house. The difference is how the dish is shaped and where the LNB (the doohicky that collects the signal) is mounted. On a prime focus dish the LNB is centered above the dish, on an offset dish the LNB is mounted at the bottom edge.
After checking LyngSat.com I found that there were several channels available via FTA. FTA, "Free To Air" means that some satellites broadcast unencrypted channels. This is free and legal. Most are religious or foreign language but several are in English. You won't get HBO or AMC... that is stealing and that won't be discussed here.
So what size of dish? SatBeams.com says that I could get away with a 24-36 inch dish for Ku-band but to get any real channels I need at least a 48 inch dish for C-band (6 foot would be better but too large for me to make). I decided on an offset dish to prevent the LNB from blocking any signal as it does on a prime focus dish. Compared to other homemade dishes mine is low tech.
Why build it? Because I can. And I like getting free TV. And as of January of this year (2015) we discontinued cable service. To go from the analog cable package we had and continue getting the channels we liked in digital would almost double our cable bill. To get local programming we have two antennas in the attic that get CJOH, CKWS, TVO, and Global (a Kosmic SuperQuad and a Super Stealh Hawk w/ZZ4 reflectors).
Recently the Puerto Rico mux left 99W, so no more NBC or FOX :(
Step 1: Software and Planning
Software used - Parabola Calculator 2.0 (on MacBook, OSX10.6.8, in WINE), Inkscape
Tools used - Jigsaw, hammer, screwdrivers, cordless drill & bits, handsaw, sheet metal cutters or tin snips
Materials used - Wood (3/8in plywood sheet, 2x2, 2x4, 2x6, 1x2, 3/8in dowel), 10in x 30 foot aluminum flashing, various screws, various hinges, bolts, washers, V-rods, shelving rod, square towel rod, 6 inch turnbuckles, 3/8in threaded rod, hose clamps, 1/2in hardware cloth/mesh, washers, nuts, bolts, L bracket (Sorry, I won't be using metric equivalents in this Instructable. 1 inch = 2.54cm)
I used Parabola Calculator to plot the curve of the dish. I chose a diameter of 108 inches with a focal diameter of 0.35, best for C-band (f/D is found under Options). Offset satellite dishes are just an oval near the edge of the full circle. Think flower petals. I made mine 54 inches long by 48 inches wide (or W x 1.10 by W (+10%)).
I used Inkscape to plan and plot out the components of the setup. Top views, side views, etc. You could use Illustrator if you have it, but I use Inkscape because it is free. (Both are vector graphics editors, that is, you create shapes and you can move them like vinyl cutouts or resize them without distortion.)
I took the measurements from Parabola Calculator and transcribed them to some bristol board. In the first picture you'll see that at 54 inches out I would need to make the mark at 19.29 inches high, then at 53 inches it would be 18.58 inches high, and so on to create the curve. From the side view the offset dish would look like the left half of the image in Parabola Calculator. I added 3cm to the bottom to give the ribs some depth.
Step 2: The Base
The base is made up of 2-2x4s and 2-2x6s with another set of 2x4s on top forming a digital "8" shape, I drilled a 1/2" hole in the center.
On top of that floats the pivoting base, 2 sheets of 3/8"x24"x48" held together with 2-2x4s and in the center a 1/2" stabilizing board with a hole in the center. A 1/2" bolt goes thru this board to the lower base. This assembly allows me to adjust the azimuth (east/west movement).
Step 3: Ribs
All the ribs are cut from 3/8" plywood, I marked my bristol board template with the various lengths of the nine ribs, five different lengths in all, No. 1 being the longest. I determined the lengths by measuring the blue lines on the plan's rib view.
Step 4: Add Ribs to Base
The rib support is a 3/8" sheet 24"x48" on which I drew an 18" half circle at the 'bottom' center, both sides. From the diagrams I transposed the angles on both sides so I could semi-accurately drill from the bottom side.
I put a frame of 2x4s around the bottom and tried to attach it to the base with hinges. It was too heavy to hold with one hand but I had a simple solution. I removed the 2x4 from the frame that would hold the hinges, attached it to the base and hinges then slid the rib support back and re-attached it with the screws.
Step 5: LNB Support
The Side LNB supports are some V-groove rods I found at the ReStore. I cut about an inch of the vee at one end so I could bend it out flat and drilled a hole for the bolts, the other end was left uncut so the two rods could 'nest' and slide back and forth. A dowel was put in the v-grove and a hose clamp was added to keep them from moving (found the idea at SatelliteGuys.com).
The same thing can be done with aluminum tube or L stock, make sure one will fit inside the other.
The Main LNB support is a 1/2" square steel towel rod sliding in a U shaped shelf support. A L piece of trim and a hose clamp act as the lock. A hole was drilled in the towel rod for the bolt to hold the LNB bracket.
All LNB supports were connected to the rib support with hinges so they could move without twisting the metal. Later on I cut holes in the sides of the dish to accommodate the side supports.
Step 6: Elevation Support
The elevation support/adjustment consists of a 2x2 and a 6" turnbuckle for fine adjustments. I cut a 3/8" threaded rod to 8" to replace one of the eyebolts in the turnbuckle, and used two-part epoxy to fix it in a hole drilled in the 2x2. A 2x4 was added later to increase the elevation. I measured the elevation with a triangular rafter square with a string weighted with a nut.
To keep the eyebolt of the turnbuckle firmly set with a lag bolt I cut a short piece of 3/8" dowel, drilled a 1/4" hole and cut it into two cylinders.
I can do fine adjustments of the elevation by turning the main body of the turnbuckle.
At this point I should have painted the exposed wood with an acrylic primer or paint.
Step 7: Flashing As Reflector
Once the ribs were in place I started cutting the flashing to fit. I first measured the length of the inside of the rib and cut a piece of flashing to match. I made a tool with a screw and a piece of wood to scribe a line about 3/8 inch down the side of the flashing to show where the rib would be underneath sheet as they would be overlapping and the top one would hide the one below.
Then I marked hole placements for the screws and used a nail and hammer to start the holes. I attached the flashing to the rib with a couple screws and used a marker on the underside of the adjoining rib. I took it off the rib, cut the sheet into a wedge, cut part of the outside curve, scribed the new edge, marked and made the new holes. Then I attached the flashing wedge to the ribs and started the next one. Because this is a low-tech build there is a lot of buckling. It took a bit of fitting and refitting to get all the ribs attached. The spread between the ribs gets up to 10 inches, these flat areas reduce the sensitivity. I cut two holes in the side panels to accommodate the side LNB supports.
Step 8: LNB Elbow
I created my own adjustable elbow from two pieces of 1x2. First I cut them into a lowercase "h" shape, adding a curve to the inside. I drilled a 1/4" hole thru both pieces of wood then I cut a small circle of 1/4" hardware cloth/metal mesh to act as a lock washer between them. I then used a bolt, washers, lock washer and nut to hold it together. It fit into the towel rod and the LNB holder.
One day I bumped the LNB Support with the lawnmower and the elbow snapped. I flipped around the black LNB holder and it works just fine. If I were to make it again I would use hardwood or plastic cutting board.
I had three LNBs set up, an EXS242 Dual output C-Band LNB, a Spitfire Elite Ku-Band LNB and a DigiWave 780 Ku-Band LNB. Only the C-Band LNB is picking up signals. All LNBs are connected with RG6 to a 4x1 switch then to a GeoSatPro MicroHD receiver. I bought it because it could record two channels while watching a third on the same transponder.
Using only a C1W-PLL lite C-band LNBF Single FTA Wideband 3.4-4.2GHz LNB after NHK (Japanese news channel in English) left 99W.
I'm using a conical scalar ring to help focus the signals to the LNB. A flat scalar ring works with prime focus dishes.
Step 9: Finished
My dish works like a 36-39 inch dish because of the large flat areas, it is not fully curved.
Gives new meaning to "Big Ugly Dish"
The photo of the Signal and Quality is of Livewell when it was still on the Puerto Rico Mux on 99W.
For now it is still pointed at 99W and we only get the eight LeSea channels, at least I get the Andy Griffith Show.
Step 10: OMG I Built a Death Ray
I finished the build in August 2013 but it didn't work right away, even with making adjustments every so often. So I left it for a while. October came and so did the time that the sun crosses the path of the satellites in geosynchronous orbit over the equator. If the system was up and running I would lose signal as the energy from the sun would overload the LNB/receiver but my experience took a different turn. I didn't paint the ALUMINUM flashing and it acted like a dull mirror and melted the cover for the LNB. I have since sprayed it with beige Krylon paint.