GH6n3 antenna build

My GH6n3 HDTV antenna build

I spent the last few days (Sept 1st, 2011) reading about antenna's. Seems the Gray-Hoverman design performs about the best. Better than commercial builds even. So I have taken on the task of building my own HDTV antenna.

All Gray-Hoverman designs are covered by GPL v3 or later as stated here.

So much for the legal stuff. Anyways after reading for several days and finding several modifications to the original design I decided to copy the work of a user by the name of nikiml. That is his handle on the digital home website. www.digitalhome.ca Clicking on the discussion forum will get you into a wealth of info about antennas and a lot of other interesting info. Enjoy.

Back to nikiml. He has his own website and several antenna's he has both modeled and built. You can find his stuff here. He has a ton of info there and if your into building your own you will find great ideas. My build will be a copy of his GH6n3. This is a GH (Gray-Hoverman) with 6 reflectors AND NARODS and 3 NAROD reflectors. The word NAROD was coined from one of the users online at digital home who came up with the idea. I think anyway. It stands for a couple of rods added to this antenna that are Neither A Reflector nOr a Director. You can read all about all that and more at the digital home link given above. By the way most of the discussion you might want to look at is under the OTA (Over the Air) discussion group and then in the Antenna Development discussion. Those are the approx names and here is a link to take you there directly.

Meanwhile I decided to build this antenna and will detail the progress as I go along. I plan on copying most of the dimensions from nikiml's site and using them as a basis for my own build. Since I don't have any CAD software here to draw the thing I have copied 3 views from his website and will spend the next couple of days plugging in all the dimensions I can find. Wish me luck. Oh and if you see any typo's please let me know so I can correct them.

Ok here is the preliminary drawing with dimensions. I will leave it to preliminary until I have rechecked and heard back from any of you folks that might have found any mistakes. Ok after a lot of experimenting I have found the numbers I had for the XYZ points had some rounding errors. I will make a whole new drawing in the next couple of days with better numbers. Meanwhile I have removed the drawings I had on here due to the inaccuracies.

GH6n3 Gen 3

This antenna was designed and modeled with 1/4" T6 aluminum and results in 300 ohm feed

The NARODs (in black) and the active element ( in blue ) should be 6 mm (or 1/4") surface to surface.

Ok I think I have all the above finished and enough info to build the antenna. You will notice there is no dimension in the width direction. Because of rounding errors I decided not to use the models Y dimensions. Since the gaps are more critical than the end points I decided to just measure over the gap distance and start the element there. Let the end of the tube fall where it may. You will also notice there is not a start point for solid elements. By that I mean there is no gap hence no way to measure over. So you just center the reflector or NORAD on the centerline. Thus giving you the proper relationship.

I did all the inch drawings in decimal as I am used to using them. If fractions are needed just convert the decimal.

I used the metric model for all dimensions. The inch model was rounded to nearest fraction giving you a bit of an error. Probably a 1/16 (.0625) or more. The metric model was accurate to .1 mm so its accuracy was about .0039 inches. Much better in my opinion. Thankfully nikimls help put me on the correct path. I can't tell you how much I appreciate his help. After all he was the brains behind all of this. All I did was juggle a few numbers.

If anyone sees any problems just let me know. I hope these drawings can help someone in the future. Meanwhile it is time for me to start building. I will take pictures as I figure out how I am going to build this thing and post them here.

9/05/2011 update

Got the material list made up for the elements. Already purchased a 1" mast of electrical PVC or whatever it is called. You know the gray stuff they sell. Also bought a 1" dowel to put in the center. This should give me good (probably overkill) rigidity. Below is the material list:

Lengths are without any radii added. Dims will need radii material added to lengths (inches). This will be applicable to the driven element only as they will be bent to form. The reflectors and NARODs will be cut lengths except for the "top hat".

NAROD reflector (red)

Top 32.016

Mid 41.362

Bot 32.016

Reflectors (green) (2ea) 3/8 dia copper tubing

top 23.96

14.858

12.543

NAROD must be same dia as driven (2) (6ga copper)

43.658 inches

Driven elements (2) 6 ga copper

57.276

Material list

6 ga copper wire

2 x 57.276 = 114.552 inches

2 x 43.658 = 87.316 inches

Total 201.868 or 16 feet 10 inches (roughly)

3/8 copper tubing

12 Reflectors (6 pairs)

4 x 23.96 = 95.84 inches

4 x 14.858 = 59.432 inches

4 x 12.53 = 50.12 inches

for about 205.392 inches

NAROD Reflectors

32.016 + 41,362 + 32.016 = 105.394 inches

Total 310.786 or 25.90 feet

So I bought a 20 foot length of 6ga copper wire and ended up buying 27 feet of 3/8" copper M tubing. This left me with little scrap but you have to plan well to get all the pieces cut out of those lengths or you will end up needing more. I bought 2 10' lengths and one 7' and I came out with about a foot of scrap.

9-21-2011 update

I have now cut all the reflector rods to length and am putting together the supports for them. I ended up using some plastic kitchen cutting boards that were approx .400" thick and with the help of my bandsaw cut them to length and notched them to accept the ends of the tubing. Pics below:

This should give you a good idea on how I plan to assemble the reflectors. Since plastic is somewhat unstable in sunlight and deteriorates over time I will be painting them to protect them from the sun. I also plan on gluing them to the copper with 2 part epoxy as that seems to be the best. I am avoiding nuts and bolts (metal) that might influence the design of the antenna.

9-26-2011 update

One of the problems I have been mulling over is how to attach the plastic parts to the copper tubing without using metal bolts/rivets etc. Today I think I have solved the problem. I went googling and finally read a posting by an automotive window installer. They said they have to use a primer that actually melts and bonds to the lexan/plastic. So I got to thinking about using PVC primer as I am sure it does that sort of thing. So my plan now is to prime all the plastic with PVC primer using 2 coats. Then spray paint all exposed surfaces with my spray primer paint. Leaving the section of plastic inside the copper tubing primed with the PVC primer. Then use gorrilla glue to hold that. After applying the gorilla glue and letting it cure I will touch up any exposed plastic or glue with the spray primer. I think this might actually work. Should keep the plastic/lexan safe from the sun rays and give me a good bond to the copper. We shall see.

9-27-2011 update

Well the PVC primer didn't seem to melt the surface of the plastic I am using. So after a generous coating, well 2 actually, of primer I put a light coating of PVC glue on each piece. The glue I KNOW melts the surface or should. Anyways I have that on now and drying. Will take a look at it in the morning and then apply my spray paint to the surfaces that will see the sun. Messy job and the surfaces aren't pretty but at least it should work. I would like to sand them all smooth but fear I will remove too much of the glue so will just paint over them and hope for the best. Pictures will be forthcoming.

10-5-2011 update

Plastic dilemma. After about a week or more of using several different glues I finally found the plastic I was using was a PP or polypropylene. After some more research I found there is not any regular glue that will hold this stuff. You CAN get a 3M glue, DP8005, but it is cost prohibitive at approximately $16 a tube (and up) and requires an applicator that costs about $50. So that is out. I am now scrapping all the plastic I had built and will make new ones out of Lexan/plexiglass and see how that goes. So much for me building this thing in a few days. lol

I have already bought a sheet of 1/4" Plexiglas at Home Depot and will try that. I am worried that it might not be strong enough so I will probably have to make some reinforcing ribs to make the pieces stronger. I guess my engineering skills will have to come into play.

Stay tuned...

11-1-2011 update

Gluing the reflectors. Well today I finally got back to the antenna project. While talking to a friend who was a plastics engineer for many years he told me to use two part epoxy to glue this together. I opted to buy a two part epoxy for plastics by Loctite corp. It seems to hold pretty well. A week or so earlier I made up new Plexiglas plates to hold the rods then today I glued the fully cured plates/rods to the mast.

Early on I had grabbed a 4x8 sheet of drywall to use as a table. I reinforced it with some wood I had laying around and put all this on top of two saw horses. Unfortunately it still didn't stay flat but was pretty close. Today I put a jack underneath the center of it to raise it so it was reasonably flat. I drew up lines on the drywall showing the position of the mast and all the rods. Then I laid all the parts on the drywall using the lines as guides. This might be easier to understand in a picture so...

As you can see in the pictures I only glued the corners of the Plexiglas plates to the mast for the moment. I plan on letting this cure and then filling in all the gaps with this epoxy. The tape you see on the copper rods were labels to tell me the lengths while assembling them. I will remove them before finalizing the build. It is hard to see in the pictures but there are lines outlining all the rods and start and stop points for the gaps. Just to make sure I didn't miss anything and to align everything during the gluing process.

By the way. Laying this all out to scale on the drywall will help in assembly as you will see if you made any mistakes in rod lengths or gaps. Don't ask me how I know. lol

11-2-2011 UPDATE

FAILED Epoxy. Well not a great day in the antenna build. Today after 24 hours cure time I picked up the mast and accidentally tapped one of the elements against the bench. It fell of very easily, detaching itself from the mast. Most of the epoxy stayed on the Plexiglas leaving very little residue on the mast. I put minimal pressure on other reflectors and each one fell off easily. The epoxy DID however adhere to the Plexiglas although I didn't put a ton of pressure on it I feel it has a good bond.

So even though the epoxy says on the package for PVC plastic it did not adhere. So I am trying another tactic. In the epoxies instructions it mentioned that if the plastic surface is smooth you should rough it up a bit. So I took a rough wood rasp and filed the attaching surface at each point the Plexiglas contacts it. Roughing it up thoroughly. I then applied PVC primer, as I felt this might help the epoxy bond. In a few moments I will mix up another batch of epoxy and apply. Waiting till tomorrow to see the results. Here is a pic of the mast.

11-3-2011 UPDATE

Epoxy results. The epoxy failed again. There was slightly higher strength to the bond but I easily removed each reflector from the mast leaving almost no epoxy on the mast itself. So today I am changing to Gorilla glue. First off I drilled 1/8" holes in the areas where the mast will contact the Plexiglas. My plan is to put glue into the holes while gluing the mast to the Plexiglas reflector plates. Then I applied a small amount of Gorilla glue to the inside end of each reflector, mostly to keep any water from entering the ends of the tubes. I sealed the inside (center) ends of the tubes not the outer ends as I will do that later. Meanwhile I will let the glue set up and see how it bonds to the Plexiglas. If that seems to bond well then I will glue up the mast and attach everything together, AGAIN!

11-4-2011 UPDATE

Design change. Well due to a suggestion by one of the folks on the antenna website I have decided to change how I attach the Plexiglas plates to the mast. Since my original idea was that the epoxy or whatever cement I used would be strong enough with my construction ideas above I have reconsidered and changed my mind. Instead of the plexiglas just touching the radius of the mast and filling in the rest with glue I have decided to cut a notch in the mast creating a small flat surface on the mast, wide enough for the plexiglas plate to contact it. Sort of a "notch" if you will. As soon as I get these notches cut in the mast I will take a picture and show exactly what I mean. Tomorrow I will make the cuts and post a picture here.

Oh and one other thing. Instead of Gorilla glue I have purchased 5 oz tubes of Weld-On #16 from a local plastics supplier. This glue SHOULD give me all the strength that I need and seems to be very highly regarded by the plastics community. Here is a link.

12-2-2011 UPDATE

One tip I want to stress is the drawing of the antenna on that 4x8 drywall. I have assembled and disassembled this thing several times and that drawing has helped me put it all back together without a hitch. It has been a real help!

I have had several things going on here that have interrupted my build. One thing was I broke a blade on my bandsaw. So I had to order a new one. This time with a spare. That and rebuilding some of the bandsaw has slowed this project down a bit.

Now I didn't take pictures of the notches I cut in the mast. But you can imagine that I just cut about a 1/4" deep notch 2 inches wide for each reflector plate to sit in. I did it all on the bandsaw then cleaned it up with a file. Not the best looking notches ever but they will be covered by the plate and glue so... Now if I only had a vertical mill I could have done a better job.

I then cleaned the old epoxy residue off the reflector plates from the previous gluing fiasco. I layed all the reflector elements out on the drawing and then placed the mast on top of them. I went back over each element and made sure it was correctly positioned in the drawing. Again I can't stress how much easier this made the assembly. Anyways last night I put the first coat of glue on all the plates. Again not gluing completely but making sure the corners at least got attached. Checking the elements this morning they all seem to be fairly strong. Looks like the glue is attaching itself to the plexiglas plates quite well. Some flex at the mast makes me a bit nervous but I will let this cure a bit more and see how it goes.

My next plan is to take the mast and elements off the drawing table and lay it on its side with the elements pointing up. Then I will lay in another coating of glue (Weldon #16) to fill in all the gaps etc on that side. Let it cure for a day then flip the whole assembly over and do the other side of the mast. This should give me a good strong bond. At least I am hoping so. I am really getting tired of tearing this thing apart and rebuilding it every week or so.

After that I plan on masking off the copper elements and spray painting all the mast and plexiglas plates to both make the build look better and to protect all surfaces from the sun. Then it will be on to building the driven element.

Stay tuned.

12-5-2011 UPDATE

Well I have all the reflectors glued to the mast via the plexiglas plates shown above. It took some doing. The glue is pretty wattery and I thought it would seep down into the cracks between the plexiglas plate and the mast pretty well. However I kept getting some air bubbles trapped beneath the glue. So ended up using a sharp object (scratch awl) to puncture the air bubbles and then poured in more glue. I finally got all the reflectors glued in securely and masked off all the copper so I can paint it tomorrow. I will take pictures and post them here.

I also bent up the first driven element. Not sure I got it very accurate though. My bends are very close to 90 degrees but I am still unsure they are correct. Tomorrow I will take another look at the model and see if my "V"s came out in the right spot. What I did was measure the length of wire in between bend points, put a mark there and then put it in a vice and bent it to the proper angle. Well close anyways. Meanwhile I didn't get sharp corners as I bent them by hand. I could have hit them with a hammer I suppose to get sharper bends but I didn't. So I have more of a radius there then a sharp bend. The length from top to bottom is not quite correct, if I missed my 90 degree by a little then that would stack with the other bends to make the overall top to bottom come out a little short or long. So tomorrow I will go back to the model and find the correct points for all of them in the Z direction and make sure all my V's are in the correct spot.

Here are some pics of the mast and reflectors before and after first coat of paint.

CLICK ON ANY PICTURE FOR FULL SIZE