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Initial Halo Fabrication

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Ok, now. How do "we" build the halo? Well, I highly recommend you read the article by Dick Stroud, W9SR in the January, 2002 issue of QST (pages 33-34). It'll help you understand the genesis of my project (and, his description(s) may be more understandable than mine...)

First, you have to start with an aluminum lawn chair. I found mine curb-side - with a "free" sign - on a Monday morning after a week-end yard sale a couple of blocks down the street. The perfect price!

You do need to be 'picky'. You are looking for an old fashioned aluminum lawn chair. The front leg "U" must measure the same width as the rear leg "U". In an unscientific study done in thrift shops and Junque Emporiums since I built this thing, I found there are quite a few 'other' styles of aluminum chairs that do not meet this requirement. But, don't be discouraged! In that case -- just get two chairs! I've even seen kiddee-sized lawn chairs of the 'correct' style that would probably make really good 2M Halo's.

You see below my first lash-up of the U-sections cut from the lawn chair, and how I solved the halo-to-mast assembly 'problem'.

Probably no two lawn chairs are the same. Dick's chair was 21.5" wide (the O.D. across each U-section.) Mine was 21" wide. So I simply added 1/4" to each arm of my U-sections. And, to be more specific on dimensions: My lawn chair tubing diameter measured out at 31/32" OD and 0.91" ID. (The lawn chair you employ will no doubt be different.)

It is easy to cut the tubing with a pipe cutter -- which gave me very neatly squared-off ends. For my design, a neatly squared-off end was important for the work I did at the gap. A pipe cutter does 'neck-in' the tubing at the point where it's cut. I used an 'appropriately sized' half-round file to clean this up. As well, since I was going to be sliding other 'objects' into these U-sections, I ran the half-round file a little further down in the tubing -- to file down the welded seam that you can feel in there.

The halo-to-mast solution was found on an old, scrap TV antenna I had. It had a round boom (versus the square box boom seen most often.) (That's it above -- as the mast in an early mock-up assembly.) The boom was 1" O.D. -- and each element mount 'saddled' the boom quite nicely. Ergo, one of them would 'saddle' my halo mast quite nicely, too. The element mounts were also more sturdy than found on box-boom TV antennas. These were 6.5" long and 1.5" wide. At the outer ends there are 'ears' to hold the TV elements locked in place. These I was able to grind down to let the 1" U-sections from the lawn chair 'nestle' into. The saddle portion of the element mount wrapped half-way around the mast -- which helped any pitch or yaw problems in my my design. The width of the mount, the ears for the halo to nestle in, and the outer bolt holes 3.5" apart gave me A Real Sturdy Halo-to-Mast Mount. (And five spares...)

Here are (pretty nearly full-sized on a 17", 1024x768 screen) close-ups of the TV element mount being used as a Halo-to-Mast mount:

The bolts are stainless steel - using SS, nylon-insert locking nuts on the backside.
Below you can see a section of scrap tubing -- cut as a half-pipe and trimmed -- that I set under the center bolt -- where the butt ends of the two U-sections meet over the mount.

What you cannot see is a 15" long piece of tubing that I found in my Scrap Aluminum Tubing Barrel, whose O.D. was exactly my halo's I.D., which I slipped into both ends of the U-sections where they meet here at the mounting block.
(Dick Stroud did this with an outside sleeve with his halo.)

What you may have noticed is that the nice saddle mount provided on the TV antenna's boom creates a 'hump' on the upper (top) side that the halo tube cannot crossover without some 'milling'. This requires that a round notch be cut out of the halo to permit it to fit over the mount and lie flat on the outer sections of the mount. With v  e  r  y   c   a  r  e  f  u  l  marking, eyeballing, and scribing, I was able to layout the cutout on the halo (assembled with just the two U-sections, the inner 15" sleeve, and the 2 outside nuts & bolts to hold it all in place.) Then I  v  e  r  y    c  a  r  e  f  u   l  l  y  made the round cutout using a 'craft' quality jig-saw table. I had never tried this stunt before, and I was pleased with how well it turned out.

The internal tube is intact -- except for the cutout -- across the butt joint of the 2 U-sections, and adds considerable support where it's needed the most.

My halo's dimensions are -- using O.D. (Outside Dimensions):

(Early on I had thought about using that old TV antenna boom as my mast. However, I was a little put off by all the holes that were in the boom. Not that I was necessarily concerned about an 'eyesore', but I was worried that the damn thing would whistle like a banshee at highway speeds! So, the boom is stowed away for some Future Project.)

(Update 2017: When I moved on to a Subaru XV Crosstrek I had to employ a longer mast than I had used with the Mercury Tracer. And I did use that blue TV boom -- which I still had after 15 years! I am reporting that it does not seem to whistle at speed -- at least not so that I can tell fron the front side of the thing at 75 mph.)

Well, now...   The halo is assembled.  How did I feed it?  How did I tune it?
Let's move on the "The Gamma Feed":

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Last updated: 07-Sep-17 -- Now "Mobile Friendly"