Sunday, August 30, 2015

Building a new beam antenna installation at N6QW ~ Part 11

More Preparations for the Rotor and Mast Installation

Since this is Part 11 you can well see that I have abandoned Roman Numerals and counting in Latin. Too bad Miss Bushnell!
This is the third day since the concrete was placed (not poured) and so it is OK now to remove the forms (yes I waited only one day). The three days is to allow the concrete to set enough to proceed with the follow on work. I can say this is not the best placing of concrete I have done but it is "good enough" for this install. The first thing I wanted to do was a "fit check" of the rotor assembly. This is where you get that sinking feeling that the anchor bolts are in the wrong place or may have shifted during the concrete placement. Well I am happy to report that the rotor plate assembly fits on the anchor bolts and you can see that below. I wear a size 10 shoe and you can see that as a reference point in the photo. (So OK I could have cropped the photo and my shoe would disappear but this does give you a size reference.)

Preparing the Mast Assembly for Installation

I must share that the SpiderBeam mast is quite well made as you would expect nothing less coming from Germany. The form, fit and function rate high marks. One operation must be done by the customer and after an explanation from the Customer Support Representative I can see the "why".
There are a whole series of additional adapter pieces beyond the basic mast. In my case I purchased the 10 Meter Heavy Duty mast and along with the mast I bought the rotor adapter module that installs in the base as well as the top section adapter that is used with their other product the Spider Beam. The basic mast bottom section is too large to fit in the typical rotor and therefore the adapter section essentially consists of short section of pipe with a larger diameter on one end about 15 CM long that inserts inside the mast bottom section and a comparable length of a smaller diameter that will fit inside the U bolts that attach the mast adapter to the rotor. Actually the short section of pipe is made of aluminum and has a singular diameter. Over the fatter end a material similar to PVC pipe is slipped over the pipe so the net diameter of the fatter section will fit inside the main mast. This PVC sleeve is bolted to the pipe using counter sunk bolts.
From the bottom of the PVC sleeve measuring about 11 CM is a through hole that will accept a 5/16 inch bolt. The purpose of this hole is to provide an anchoring of the mast to the adapter. Enter the first small problem -- there is no matching hole in the mast base section. This is where the customer is required to accurately drill that hole so that a 4 inch long 5/16 inch bolt can be passed through the mast and adapter plate which will prevent the situation where rotor is rotating but the mast doesn't move. It also serves the purpose that if the rotor has a brake lock any wind forces on the beam will not move the antenna. A single bolt provides an important function.
At this point you would ask why doesn't the mast assembly already come with a hole drilled at the right location. Well that seems like a reasonable assumption from a customer --hey the mast can be bottom rotated and the adapter (quite well made) is factory provided so why no matching hole in the mast.
Well I am thinking back to when I had a NIB 1966 yellow Volkswagen and to my surprise there was no hood lock and within a week my spare tire was stolen --and might I add there was no spare tire lock. So when I purchased a new spare tire, at the same dealer where I bought the car, the sales person said you better purchase the spare tire lock. So I said give me one and being in a hurry since I was on my lunch hour, I simply locked the spare tire and the lock inside the car.
Later that evening when I went to install the spare tire lock I laughed out loud and my first words were "German Engineering". The spare tire lock consisted of a piece of chain, a large bolt and a padlock. The install entailed removing a bolt which attached part of the body to the frame located behind the spare tire. After removing this bolt you passed the longer kit bolt through the end of the chain and installed it in the vacant hole. Then placing the spare tire in its location you ran the chain through one of the lugs and next put the padlock on the chain. So the same question --why didn't this come like that from the factory --the cost was $13.
The answer from SpiderMast Customer Support was that few masts are sold to be rotated at the bottom as most masts are used in portable operations and are turned using the Armstrong Method. (ie hand rotation). I also was told that many of the masts are used for applications other than ham radio and therefore not rotated. So to have masts with and without holes would involve multiple part numbers and since the usage with bottom rotators is small -- the task is left to the customer. I am sure that was the same answer for the spare tire lock -- German Engineering!
The thought just occurred to me --any chance the guy who designed the spare tire lock now works for SpiderBeam?

How to drill a straight hole through the mast?

So OK the customer has to drill the hole. This is where you spend considerable time noodling (my term for thinking) the problem. There are at least three issues with the first being you only want to drill through the bottom section. With the mast nested literally all of the sections are in the hole location with the mast retracted. So the mast sections above the bottom section must be pulled out a bit so that you are only drilling the bottom section. [This was a caution from Customer Support --so others must have drilled through all of the sections.]
In looking at the adapter section a fit check in the rotator with the adapter installed it was clear that there should be about 1/8 inch clearance so that the PVC sleeve will extend about 1/8 inch below the mast. Why? Because there is just enough of the bottom section to fit within the jaws of the rotator (Yaesu G450) thus if you made the mast align with the bottom of the sleeve there may be interference with the top of the rotator housing. This is just to give you some breathing space. So allowing for this I decided the center of the hole through the mast should be about 10.5 CM. I placed a dot (magic marker) on the mast section at 10.5 CM and then placed the mast adapter near the hole and saw that the center of the adapter when aligned with the proposed hole would give the 1/8 inch clearance at the bottom. So we are ready for the next step.
To assure that the hole is drilled properly several things must happen. First you want the mast section to be "captured" so that when you are drilling there is no movement of the mast. This is easily done using four piece of scrap wood. I happen to have a small box of cut off pieces of 2X4 and this is a perfect size. So Ok I am about to put several nails in the top of my homebrew wooden workbench. Starting with two pieces of the cut off 2X4 pieces, I temporarily nailed them about 12 inches from the front edge of the bench and these are spaced about 4 foot apart. Next I laid down the mast along the length and marked the position of the other two blocks as they were butted up against the mast and then installed the last two wood blocks. These four block form a "crib" assembly to keep the mast from moving around while your drill.
The next step involves placing the mast assembly in the crib holder and finding the mark at 10.5 CM. Before drilling align that mark so it is square on the top dead center and so the mark should visually appear equidistant between the two pieces of 2X4. The final hole size is 5/16 so you will need a 5/16 inch drill bit at least four inches long. DON'T start the drilling process with this size instead you want to be "stealthy" initially starting with a 1/16 inch bit which essentially is a pilot hole. The using four or 5 sizes of drill bits each progressively larger drill the hole to size. Slow drill speeds are best and KEEP the drill vertical!
Now with one hole completed we are ready for the second hole. We start by inspecting the first hole by looking inside the mast section from the open end and evaluate if there are any burrs or other debris. This foreign matter can be easily removed using a long screwdriver with a thin blade. The next step involves placing the adapter assembly inside the mast and aligning the hole in the adapter with the hole in the mast. Now insert your drill into the first two aligned holes and carefully feel the drill bit seating in the second hole in the adapter. The adapter is now serving as a drill jig. I should mention that I placed a small square of plastic material about 1/16 inch thick between the underside of the bottom mast section and the workbench top so when the drill bit clears the metal, the plastic acts as a backstop to prevent drilling a 5/16 inch hole in the top of my workbench. With all in place and keeping the drill vertical slowly begin drill the second hole. This process worked perfectly and the holes are properly aligned and square with the world. Below are some photos of the finished assembly.

Critical Success Factors!

  • Measure 40 times and Cut Once.

  • Use the proper tools

  • Slow Drilling and proper hold down of the part being drilled

  • Check your work and noodle through each step

Pete N6QW