Introduction: Build a Large DB8 HDTV Antenna: Big Bertha
Update May 2015: this antenna was built in 2009. It is now 2015. We still have it and it's still doing it's job. I've since put an amplifier on the mast and we now can get that fringe channel lightly to the left of the others without any longer having to use the rotor to turn it. Actually, I leave it set facing the fringe channel and the stronger ones are the ones that compensate. I go up on the roof to check things every couple of years and so far all is well. I would recommend stainless hardware throughout if doing this. My plated stuff is doing well but stainless would have given many, many years of carefree use. Oh, I also now have a 60" Sony Bravia LED instead of the old Sony analog TV we had at the time of the original construction.
We've had Cable TV and Cable Internet. It seems that there is less and less on cable than there ever was. Cable in my area is $49. I eventually cut down to basic for $20 and supplemented with Netflix. Netflix is excellent by the way but that's another story. We also have my macintosh connected to the TV so we can Hulu any program that played recently.
I'm finding that even basic cable has little 'value'. By value I mean I get the basic local channels and a bunch of junk otherwise. The channels I look at I could get for free if I used an antenna. Hence, I've decided to minimize.
Here in Southern Maine the TV stations are mostly in Portland about 30 miles away. Some are further, about 50-60 miles away. Most HDTV antennas work for 30 miles and a few claim to get up to 60 miles. I decided that I need more antenna than that. Something where 60 miles might be the limit but a doable and good limit. I've decided to produce a DB8. A DB8 antenna has 8 receiving elements, or 4 pairs of elements. It's basically two DB4 antenna's combined. The last picture in the segment is a commercial one.
What follows is my foray into the world of HDTV antenna construction and trying to squeak the most out of it for a moderately fringe TV area I live in.
BTW, the last segment contains all kinds of HDTV signal information and links to places to assist you in learning more. I was a teacher for 30 years (no I don't want any help with my grammar, I said I used to be a teacher) My job was simplification and clarity. I hope this instrucatble is up to that.
Step 1: Plans and Measurements
I want to give credit to this website for the dimensions for the antenna. And the diagrams uploaded as part of this instructable. At the site you can find a bit more information.
The measurements should be exact or as exactly as you can get them. I will describe the materials as the steps to building this occur. Most of the actual antenna construction part can be purchased at Home Depot which is where I got the raw construction materials.
The first diagram gives the overall dimensions of one array.
The second diagram shows the wiring and dimensions of the wiskers
The third diagram shows the measurements of the wiring
I suggest you print these three pages.
Step 2: Building the Reflector
The reflector can be made of any metal. You could use a solid sheet but in a big wind it would be a problem. And all that is really needed is horizontal bars or wire that are separated by no more than 2 inches vertically. Anything larger than that and it would exceed the wavelength and would not reflect the signal to the wiskers. I found some 36" wide rolls of something called galvenized wire netting at Home Depot. It's got 1/2 inch squares of stiff galvenized wire that is welded at each crosslink. The 36" is perfect for the width of the array. Wider could be used but it would go wasted as the reflected signal wouldn't hit anything useful.
Unroll 40 inches (for the hight) and cut it with snips. To reinforce the sides (40" side) I used thin 1/4" wide angled aluminum trim. I placed one side of it under the mesh and pounded it over with a hammer.
Picture 2 shows this more clearly. I then turned it over and pounded the other side to flatten the mesh as the aluminum tended to curl in the direction of pounding. Do the same thing to the other side.
Next, use two, thick, 1inch wide X 36 inches long aluminum bar to reinforce the top and bottom. As the measurements show the two sides of the array are wings that will be slightly folded in. Place the bar in a vise and bend 10 inches of the bar 2 1/2 inches forward. Do the same to the other end. To assist, make a wedge 10 inches long and 2 1/2 inches wide out of hardboard to act as a guide. Or just measure it. Make another angled brace for the bottom of the array.
To prepare to install the two bent top and bottom braces, measure 10 inches of the side of the mesh and bend it slightly on the edge of the workbench. Do the same to the other side.
The bar is on the bench with a final angle check. Drill small holes. 2 on each end of the angled bend and one in the center of entire bar. I used 3/4" size 8 machine screws and nuts with washers on each side to bolt the bar to the FRONT of the mesh. Bolt one to the top and one to the bottom.
Step 3: Spline
For all the solid bracing you could use a number of materials. Wood would work but it might rot over time. I chose to use plastic board. It's the stuff they often use to do the eves of houses now. It's white, tough and work much like wood. It's also pretty expensive. It's up to you.
Cut the spline the hight of the reflector (40") and drill and bolt to the top and bottom of the BACK of the reflector. Be sure to use a washer on the spline side. I also used a small lock washer. I expect wind will rock the reflector back and forth and don't want the nuts coming loose.
The pictures below just show three views of this step.
Step 4: Preparing Forward Whisker Brace
The V shaped wiskers will need to be mounted ahead of the reflector. A brace 29" long (the distance from the top to bottom wisker is 27") is made from the same material as the back brace.
Use a large drill (forstner bit works nicely) to drill a recess for each of the eight wiskers. use the diagrams from step two to determine the distance apart they should be. About a 1/4" deep should be enough. Notice that the recess is of the side of the brace. This is to accomodate the wiskers sticking out.
Drill the center of the recesses to accept a machine screw.
Step 5: Preparing Phase Line and Whiskers
Phase line: the wires that connect the wiskers together. See the diagram. I used #12 copper house wire.
Whiskers: The wires that produce the V shaped elements. I splurged and purchased some bare solid copper #6 wire off the roll at home depot. I bought 30 feet of it and have about 2 feet left. I bought enough because we're building two of these things here and hooking them together. If you're only building one then 16 feet should be sufficient with a bit left over. I built two so I could connect them together and maximize my signal collection. One of these is good for 30 mile reception.
You can use smaller wire for the whiskers but it might no stay in the correct configuration over time as movement of the antenna might alter their shape.
Use the phase line diagram in step 2 to determine measurements.
I stripped the plastic of the house wire to obtain a length of plastic coated white and black copper wire. I wanted the plastic coating to stay on the wire everywhere except the place where it connected to the whiskers with a screw.
shape the two wires as shown in the diagram. Make loops where it will go under a screw. make sure the loops coincide with the depressions you drilled in the front brace. Be sure to make a loop for the center. This is where the antenna wire will connect when it is mounted on the roof.
Picture 1 and 2
I wanted the plastic insulation off the loops but cutting it off was getting tedious. So, I fired up the propane torch and melted it off. With a little sandpaper the loop came clean.
Pictures 3 and 4
Cut 8 pieces of the #6 copper wire for the wiskers. In the end each whisker should be 9 1/2" long. So cut it the wire 18". I found that an extra inch helped out. You can always cut any excess length off after.
Bend the wire in half around a bolt in a vise. and pound it together, then use pliers to spread the whiskers apart in a V shape.
Seat the V of the whisker in the recess, Place the phase line wire loop over it, add a screw, with washers on both sides and squeeze it in place by tightening the nut. Do the same for all 8 whiskers.
Step 6: Mounting the Whisker Spline to the Reflector
The following pictures are just various views of the same thing. The whisker spline mounted to the reflector. this mounting can be accomplished many ways. You could cut pieces of plastic pipe and use it as spacers for example. I decided to use some more of the plastic board to create a fin between the splines. I thinned it out a bit on my planer (if it looks thinner to you).
It is attached to the rear and front spline with 2 inch galvanized sheetrock screws. 5 or 6 on each side. It seems solid. Be sure to notice the measurement parameters on the diagrams for how high it needs to be raised.
Also notice the whiskers have been bent forwards 2 1/2 inches to coincide with the wings of the reflector. In actuality, this thing could have been made flat. But only the reflector directly behind the whiskers would have deflected a signal to them. The bent configuration creates slightly more reflection and therefore slightly more signal to the whiskers. But not much. Remember, I'm looking for fringe signals. You may not be in that position. Stations might be closer for you.
Step 7: Ganging Two Arrays (optional)
As you can see in the following pictures I created two reflectors to put them together to make an array. One reflector will work perfectly well for up to about 30 miles from a station. Two arrays won't give you double the distance but almost. And I'm counting on the design of these antennas to actually be over 30 miles for one and at least 60 miles for two.
I ganged them together using think 1" aluminum angle bar. I simply drilled and bolted them across the top and bottom of the flat bar braces. I used two screws on each side, so four screws for the top and four for the bottom.
The center of this whole thing is where my U bolts will be placed to mount to the mast pipe. If you use only one reflector then it would go in the center of that reflector.
These reflectors can also be mounted one above the other on the mast but you'd need a longer mast pipe and doing so might facilitate having to use guy wires to steady it in a wind. Alignment is fairly specific for HDTV signals. A bobbing, waving antenna might be an issue.
If you decide to just have one antenna then skip to the section on connecting them. It will be simpler.
Step 8: Connecting Your Antenna Array
Please remember that all connection instructions are your responsibility. If you feel uncomfortable on a roof doing this or with grounding properly for lightning then have it done professionally. Basically this means that I absolve myself all responsibility in this area.
How you mount your antenna is your business. There are several mounting masts available. I'm mounting mine to my chimney. Using a set of stainless straps that wrap around the chimney for just this purpose. My chimney isn't being used. If yours is, especially for wood or coal I suggest another spot. Your antenna will be soon covered with soot if you use the chimney. Two things are important.
One is that if you can get higher, the higher the better. Mine will be 10 feet above the roof. Remember though that anything much over that should have guy wires to steady it.
Secondly, if the stations are not all in one location, like a city, then you'll need an antenna rotor to turn the antenna the desired direction to the station. See the last chapter of this instructable to find out where your stations are located.
Connecting the antenna
If you just made one antenna then you'll only need the balun, lightning arrestor and coaxial cables. Connect the two leads of the balun to the too center loops of the antenna phase line. Connect with screw, nut and washers keep it loose or drill and bolt it to the standout board if you want. connect the other end to a short coaxial cable. Screw a lightning arrestor to the pipe and connect the other end of the coax to it. The other terminal on the arrestor goes to the TV or DTV converter box.
If you've got two antenna's like I do then you'll have to use to balun's and a splitter (or in this case a splitter acting as a combiner) mounted between the antennas. the diagram should explain this.
I recommend that all connections either be wrapped nicely with electrical tape, or coated with silicon II that hardens (outdoor silicon caulking is fine) or use coax with weatherproof boots on the connections.
Grounding your mast
It is very important that you ground the antenna and mast. You'll need to get a ground rod and connector made for this and a length of aluminum grounding wire. Attach the ground wire to the antenna mast with a screw or clamp and run it to the ground rod that has been driven into the ground. Securely attach it to the ground rod with a screw clamp made for this.
Step 9: Up on the Roof!
This series of pictures just shows the assembled antenna up on the roof.
The first picture shows one of many ways it can be done. I have an unused chimney that is large and strong. I chose a chimney strap system. It consists of two corner brackets and stainless straps that go around the chimney. Turnbuckle type bolts let you tighten it. The mount is strong. You can also get roof mounts in various configurations. One of the best and least invasive are the brackets that mount on the side of a house at the peak. No holes in the roof and you can screw into solid wood.
The second picture shows one half of the array and how the matching transformer is connected. I attached the leads with stainless steel machine screws with washers on both sides and a nut. Then ran the bolt through the white plastic to brace and bolted the connection to it.
The third picture is of the splitter being used as a combiner. A coax from each elements matching transformer is connected here so they antennas can be 'combined' into one cable. This splitter actually degrades a bit of the signal but the second element will bring in enough extra signal to make it worthwhile.
The fourth picture: Bolted to the mast pipe is the coax grounding lug. The short length of coax from the splitter is on one side and the other side is the coax to the TV. The ground wire is connected to the lower pipe and goes to a ground rod. There is a grounding screw on the grounding lug that the ground wire can be attached to. My wire is attached to the mast below the rotor.
Here you also see my channel master rotor. Where I am the signals are within a 20 degree arc with some of them being 180 degrees to the rear.
The fifth picture shows the entire antenna from the front.
Step 10: The Visual Results
The digital tv converter box I chose is the Digital Stream DSP7700P Digital Set-Top Box. There are many to choose from. Some have much better reviews than others. But, there are enough horror stories for each box to make you think that all of them will be a lemon. And at this time not many are available since the government coupon deadline is over. This one seems to be working well.
The second picture shows the back of the converter box. Simple really. Coax antenna in and coax out to TV or you can connect your TV via the analog RCA jacks. Your choice. The box has an on button and channel up/down buttons. It comes with a infrared remote that has more bells and whistles. The instructions are sequential and fairly clear. You can see a signal strength and scan for channels that lock in when done. There are full menu items for a variety of functions.
Where I live in Southern Maine there are three locl channels NBC, ABC, and CBS that are 25-35 miles away. I live on a lake and therefore a valley that is low and surrounded by hills. Trees are also all around my house and the leaves are still on them. My antenna is about 20 feet above ground.
There are three public television stations 7-35 miles away and Fox movie station where american idol exists. So, the wife would like to get that. The only problem is that Fox is 62 miles away. Definitely a fringe station.
The closest station NBC has a signal strength of 88-90 and very strong. ABC and CBS have lower but still strong signals. ABC is further away but the antenna is atop Mt. Washington so, a good signal. Picture three shows the signal strength for NBC.
The fourth picture shows the signal strength for Fox at 62 miles away. The signal strength is 30% which is more than enough for viewing. A strength of 5-10 should be enough but with this station at least 18 is needed. With digital signals the picture is usually always good if you can see it. Snow on the screen is only for analog signals. At 18 though some blocky artifacts can sometimes be seen. This signal was supposed to be the litmus test for my antenna. My neighbor with a db4 an amplifier can't get this station.
The last picture is of the trees in the direction most of my stations need to deal with. Trees aren't good but the antenna seems to not be bothered by them. The leaves will soon be down.
Overall the construction experience has been pretty good. I had a lot of fun and learned a lot in the process. I hope the info here is correct. I'm no expert for sure. I ended up getting the three networks and Fox, three public television stations, and a couple of smaller local stations. BTW one of the good ones ABC is a VHF not UHF station. This often requires a VHF antenna. The strong signal along with the strong antenna seems to make this unnecessary. After the weekend I will be giving Cable TV back their signal.
Thanks for reading,
Step 11: Digital Signal Strength 101
There are tools on the internet to help you determine the stations in your area, their power, distance, and your chances of getting them to show on your TV.
I suggest you try 'TV Maps' link. Type in your address, height of your antenna and you can determine your chances of reception.
You'll also see a list of stations in your area. If you choose one you'll see a color coded map of signal strength from the station to your location. The list shows the distance in miles and and important number NM or noise margin. The antenna we're making should have a gain of at least 15, hopefully more. Think of the NM as the loss of the signal to your house. It could be hills, leaves, walls or weather. It's also distance and location of you and the signal tower. The goal is to get a net gain of at least 0. At zero you'll get a signal. For a reliable signal a higher number is beneficial. 5-10 means you'll probably get a signal over 0 consistantly.
So, take your antenna gain. Let's use 15 and add the NM For the positive numbers it's no problem. The negative numbers might be another issue. An antenna of 15 db hoping to get a stations that's -11 db leaves a net gain of 4. Marginal but a reliable steady signal is possible at this level. The thing is every splitter, length of cable, branch in front of the antenna, Snow in the air, and many other factors can lower the db of gain bringing that gain of 4 down to 0 or lower meaning loss of signal.