The
6M
Halo Antenna
Photo courtesy of KB1DIG
I was inspired to construct this page by Steve's, N1TYH, enthusiasm regarding the building of this home brew 6M omni-directional halo antenna based on Steve, KB1DIG's website. Both N1TYH and myself are building this antenna using a few different building techniques that worked for us. I have never been on 6M as a ham of 26 years and now with the Kenwood TS-2000, I wanted to get on 6M easily but without exhausting my retirement budget and Steve, N1YTH, a newer ham, waiting, like me, for those grid squares and DX contacts.
I thank Steve, N1TYH for rekindling my desire to homebrew antennas and helping me out in parts of the building process I could never do. In return, I was able to obtain parts which, in turn, helped Steve. And I thank "other" Steve, KB1DIG for allowing us permission to connect his site with mine and to add our building techniques to his and from which you will probably improve upon the three of us techniques even more!
As the original design plans are here on KB1DIG's web site, you should go there first because this information are on his photos, dimensions, and plans for his omni-directional halo antenna. I recommend printing his halo antenna page out so that you can study it in greater detail. Do not forget to view the "Some Comments about the 6 meter Halo Antenna" section as he has posted some other critical dimensions to the antenna construction plans. Afterwards, come back here to take a look and see how we built it as partners in the true spirit of ham radio. Before building, CLICK HERE to get a PDF file to print & read this whole page easily before any construction.
List of materials:
1. 2 3/8th in. 60" long aluminum fuel lines (from a
NAPA auto parts supply store; they stock all lengths)
2. 1 3/8th in. 18" long aluminum fuel line
3. Aluminum block as per KB1DIG's specifications
4. 2 1 1/2" muffler clamps (again NAPA)
5. 1 piece of 14" long RG8 cable with the outside cover and
shield removed
6. 2 #8 metric bolts
7. 1 Bernz-O-Matic aluminum brazing/welding rod
8. 1 household welding torch
9. 3' x 3' piece of plywood
10. 3-4 vice grips
11. Rubber mallet
12. Pencil, string, and center punch or metal with a point to stay in
place while you draw an arc
13. Calterm brand rubber insulated clamps (P/N 67791) from
Home Depot...2 pieces per bag for tuning stub minus the
rubber insulation that you just pop
out. Thank you N1TYH for picking those out for me...was very crucial
14. A 6M SWR meter...thanks again to N1TYH
15. Silicone Rubber Sealer from Radio Shack (P/N 64-2314b) $3.19
16. Mast (your choice of height) from Radio Shack ($10.49 for a 5'
section)
17. 2 fiberglass rods for antenna support Home Depot .....$1.99 for a
4ft. piece...... orange & white markers poles to
mark edges of driveways in winter. (They will be
spray painted).
18. 1 can flat black spray paint
19. Plastic wire ties
20. SO-239 connector and either pop rivets or small 6/32 seconds screws and/or
nuts & bolts to attach SO-239 to block
21. Strip of aluminum and bolts and screws to make gamma match strip.
22. Work bench (Black and Decker Workmate workbench with adjustable table
sections act as a vice for the template)
23. Safety goggles when soldering and drilling
Shaping the Elements:
Fuel line work: If you purchase fuel line in a coil, it will be easier for you to create the arc so that the whole halo is an softer. NAPA fuel line is much harder and, as such, I needed to make a template by which I can create the perfect arc so the antenna at least LOOKS like a halo. If you have softer fuel line, forming it by hand/eye coordination is good if your hands and eyes are coordinated too (: but this will work for softer metal also.
From KB1DIG's diagrams, you will see that each element is 54 inches long. Because my fuel line was harder, I had to make a plywood template that would yield a perfect half circle for a 54" piece of line. For this, you must use math and calculate the radius it would take to make the 54" two elements into a nice looking circle. For that we need to find the circumference of whole circle of 108" (the two 54" halves).
Here is the formula: If
C = 108”
Then C = Pi (3.1416) x d
R = d/2
Solve for R
In my case R = 17.14 inches
Drawing the Arc:
1. Take a sharp pencil, string, and a piece of metal with a
point...I used a center punch
2. Secure a string between the pencil and the center punch;
once tied,
measure carefully that the string is the length of "r"
above.
3. On the plywood board measure the exact center of the
bottom of the board. Place the metal marker on that
spot and with the pencil at the other end
of the string, slowly draw an arc across then plywood. Use a saber saw
and cut out the template. You will now have
a perfect 1/2 circle with the proper radius for a 54" length to form your
elements.
Forming the Elements:
1. Place the entire plywood template in a locking vise such as a B&D Shop mate workbench.
2. Using three or four vise grips attach the vice grip to the
template with the straight fuel line across the top
of the template. Use the rubber mallet to
bend about 3-4 inches at a time around the template. If you use NAPA
fuel line, you can hit it as hard as you
want with the mallet; the fuel line won't dent but be patient on this step.
3. Do the same thing with the 14" line which will be the gamma
match with the same radius. When done, your
elements will look like this:
IMPORTANT:
Be sure to keep a flange on each end of the two
elements it provides further surface contact and strength
when you weld the flanged end with the bolt in it to the aluminum block. The
block "bites" the inside of the element so
it isn't destroyed. The reason that it is a metric bolt is that 3/8' bolt will
destroy the tubing and the very next size
down, 5/16th" is to small. The metric bolt is in between those sizes and does
nicely. You don't need the flange
on one
end of the gamma match section
so file it off with a fine metal file.
The Aluminum Block:
This part of the project was built and written by Steve, N1TYH
1. I printed out Steve's ( KB1DIG) template and
it happens to be 1:1
2. I cut a few notches in the paper in areas where I
wasn't going to drill.
3. Then I secured the template to the top of the pre-cut
(2" X 4" X 0.25") Aluminum plate using clear packaging tape
(covering the entire template). The notches
allow the tape to grab the top of the template.
4. The tape over the entire template, prevents the template
from ripping to shreds when the drill goes through.
5. Then I simply put the drill bit into the milling
machine and followed the hole locations on the template.
What I'd do different next time:
1. I'd print out the template on Avery label stock,
thus avoiding the need to cut notches and also eliminating the shipping
tape.
2. I'd have the dimensions of the fuel line ahead of
time, so that I'd mill out the right diameter the first time.
3. I used the 6-32 threads to secure
the SO-239.
The Assembly Process:
It's now it's finally time to put the whole thing together. First though, here is a photo of the aluminum block made for me by Steve, N1TYH. We found that the clamp holes where too small for our clamps that will fit snuggly with Radio Shack 1 1/2" OD mast. I drilled out the clamp mount holes for a standard 1 1/2" inch muffler clamp. Use a 5/16th drill bit without a pointed tip! Use a drill bit whose cutting edges contact the surface, slow speed until the bit centers itself, then increase drill speed to finish widening the hole. If you have not drilled any holes yet, then 5/16th drill with a center point bit is the size you'll need.
4 5/16th holes and SO-239 drillout
Upper left holes are for the elements and right side holes for brackets
The center conductor of the stripped down RG-8 in the gamma element will be
soldered to the center pin of the SO-239
Welding:
Just a note on welding...but sure that the bolt passing through the block
into the elements has a bite on the element. This adds to more stability to the
them.
I did one weld in the basement which is ventilated but my alarms went off
away.... the welds took very well. The alum
rod and block has to be hot enough for the alum rod material to flow and set.
Aluminum heats up quickly so don't overcook as I almost did.
A good weld will somewhat dull and runs...it will flow into the joint and have
that dull color. A cold solder/weld joint will be somewhat shiny and lumpy, will not flow,
and does not adhere to any pieces of the metal i.e. a cold solder joint. It is the same principle as
Basic Soldering 101. If you built Heathkit products as I have years ago, you
will know exactly what I mean.
I am unable to show you photos of the weld as my digital camera does not have a lens for close up photos so check KB1DIG's site that does have good photos of a good weld.
Once set with a good weld with the bolts, very strong bond is now made so next step is to place the plastic tubing insert over the two ends of each element.
The Plastic Insert:
My local hardware store had 9/16" OD clear tubing with a 3/8th" ID. It is made of clear vinyl and I'm sure the sun will eventually break it down but I check my antennas every year and changing the tubing is no problem....especially when it's only .14 a foot so I bought a few extra feet and used about 8" on the antenna. I have the two elements spaced apart one inch.
SO-239:
At this stage just attach the SO-239 with the 6/32 bolts and nuts or screws if you thread the block. No problem here.
The Gamma Match:
Cut the gamma match to 14" and insert the piece of stripped down 14" coax into it. Solder the center conductor to the pin on the SO-239. You'll notice this piece of insulted center conductor slides through with great ease. ...important feature when it comes to tuning. Take the two Calterm clips and remove the rubber insulation...it peel right off. Shape one around the element next to the gamma match and the other to the gamma match itself. Use a good size bolt, washer, and nut and really tighten it down. You may have to use needle nose pliers to get that space where the top and bottom of the clip meet to really shape it to the gamma match and element circumference.
SWR Adjustments:
This is the toughest part of the whole project I encountered. There are three variables to getting a good match. In math, if you know even one of the variables, like 54" = b + c, this would be an easier exercise in tuning...but it's not. We have a = b + c ; three variables to adjust to get a good match. The first is the amount of RG-8 cable exposed when you slide it in and out the gamma match. The second the distance between the gamma match and it's neighboring 54" element. The third is the length and the distance along the tuning stub connecting the gamma match and it's attached element. Fortunately, Steve picked up the Calterm brand clips which just happened to be the exact length of the tuning stub needed. One variable solved in hind site.
Borrowing N1TYH's 6M SWR meter, I uncoiled the coax in the shack and placed the antenna on three non-conductive pieces of furniture. IMPORTANT: To begin the SWR adjustments, I used only 10 watts and no more to tune the antenna on the desired section of 6M I wanted to use...50.125. By moving all the three pieces while sitting down in the shack and viewing the meter at the same time, the first reading of 8:1 was brought down to 4:1. That's the break I needed. I also noticed that as I lifted it up off the supports, the SWR went down a little further.
At this point, I now mounted the antenna on a 5' mast and placed it on my back porch which is one story above ground and at eye height when looking it. I then ran the coax through the hallway, through the dining room, out the back door, and connected it to the antenna. Here is where the exercise comes in but you know that you have a closer match now. By a combination of sliding the coax in and out of the gamma match and then making a subsequent trips to adjust the tuning stub without moving the gamma match , it took me about a dozen or so trips back and forth to read the SWR meter and adjust different parts of the antenna when unexpectedly, I had a match of 1.6:1 which is good enough to me. Remember from your reading of antenna books that any match at 2.0:1 is OK.....actually trying to get it at 1.5:1 is almost folly but the expected standard and don't bother trying to get a flat match as that is just an act of diminishing returns and a TON more work and makes NO significant difference in your TX/RX signal strength. 1.6:1 from 50.100 all the way up to 50.500 worked for me.
I then contacted N1TYH and asked if he was available for a test QSO. Steve lives about three towns apart from me, 10-12 miles away, and the 2nd largest city in MA, Worcester, lie between us. When we hooked up, and we had arm chair copy on both sides, my 100 watts from the TS2K rig. I yakked for at least 45 minutes total. Thanks for taking the punishment Steve, who, BTW, will be building his own halo as he has a Diamond V2000A now a "quasi' vertical.
Mounting on the Mast;
I mounted my antenna to the mast just a bit different from KB1DIG's method. It just seemed to work for me....so do what works as long as is secured tightly.
You may also notice the white goop over the entire plate. I admit it isn't pretty or a showcase antenna for any antenna page or book. I used the Radio Shack silicone rubber on the entire aluminum plate both sides protecting the SO-239 pin, the welds, everything from weather and oxidation. I also gooped the entire tuning stub so it would not move during windy WX and not oxidize. I also gooped the end of the gamma match so I didn't need the black cap as well the point where the gamma match where the coax emerges from of the gamma element to the center SO-239 pin to make sure no water would enter that end of gamma match either. The next morning everything was stiff and set.... NOT pretty site, but then again, neither am I (:
Final steps: The fiberglass supports and adding more mast.
Adding the fiberglass rods is an easy step...I bought two four footers and painted them flat black instead of white and orange. I used two wire ties criss-crossed on each element and smothered them both with the clear rubber silicone. At the mast, I used three wire ties for extra support and also sealed it in silicone.
The orange
tips were in the ground when I spray painted the rods. I have since painted them
black
The Good News: The assembly of these rods were no problem and really gives the other end of the halo rigid support.
The Bad News: This changed the SWR to a higher value and had to fiddle with the stub and gamma match again so make sure to include this step. After several adjustments and from what I learned the first time, this was really not a problem.
The Mast:
At this point I am now on the final stage of the whole project. I used 20' of Radio Shack mast. First I painted them all flat black as navy steel grey is unsightly and the flat black won't shine & be noticed as much as it blends into the landscape much more easily. I made another support at the top of the railing corner in the picture above (but not shown) From ground to top of the halo is about 35 feet and I might add another ten foot section and guy wires.
The Cable:
Before the antenna was hosted up on the mast, I made sure the coax was supported by one of the bolts before heading down the mast. I also made sure I had silicone all over the connector for WX protection.
In my case I ran the cable along my second story porch, up through the vents in the eves of the roof and ran a stretch of cable across the attic and down into my shack...total length need for me from antenna to rig was 70 feet. An SWR check showed the same 1.7:1 and I am happy and up and running. Now I just have to keep a sticky note of the DX and USA calling frequencies and reminder to QSY off those window frequencies when a contact is made.
Final Photos:
Here are a few of the photos of the antenna now that the project is over. Though I have had just a couple of contacts, signal and audio reports were great.
If you would like to get in touch with any of us, here are our e-mail address. Just click on the call(s) below. We would be interested in reading your comments and any other suggestions that might improve the antenna. Again thanks to KB1DIG for doing the yeoman's job on this antenna and his inspirational e-mails back and forth and N1TYH for his alum block mill work and use of his 6M SWR meter!.
Final Test:
Again N1KYH & I had a QSO and was arm chair copy with very low SWR. To our surprise, N1EUX from Mason, NH came in and gave us great signal reports. Mason, NH is a fair piece considering we live closer to the CT state line! Well, there's state #2 so 48 to go (: Thank you Al!
Blends in on a cloudy day......................on a sunny
day.........................not too bad against a blue sky
.....Now we all hope to hear you on 6 meters! GL, good DX, and 73......
Steve KB1DIG Steve N1TYH Frank NG1I