The 3 G Project – Part 3

31May09

After researching antenna mounting options for the last couple of weeks, I’ve come up with a hybrid design of sorts.  It will incorporate features of ridgemount and tilt-over designs, and will additionally employ guying for stability.  Aside from the goal of performing well, my secondary requirements are that it causes as little destruction to the roof as possible, and that it not be immediately visible from the main road or the front yard. 

I’m going with the tilt-over design (it will employ a winch for raising and lowering the mast) because I want easy access to the antenna if I need to make changes.  I’d also like to be able to raise and lower the mast without needing anyone else on site to assist.  The ridgemount feature will let me take the advantage of starting my tilt-over at a base height of 18 feet by mounting on the peak of the roof.  That’s more than a third of the way to my goal, which is to have the antenna sit at, or higher than, 50 feet. 

Although I won’t have LOS (line-of-sight) to my target at this distance, getting above the average tree-line altitude will remove as many obstacles from the signal path as possible.  besides, I have a lot better chance of finding a usable signal at 50 feet than I do at 20 or 30.

Before I grabbed my materials and headed for the roofline I decided to check the temperature.

It's going to be warm today

It's going to be warm today

 I guess it could be worse- it could be humid but fortunately it is not- still, the thermometer is reading about 86 and it’s only 10 AM.  Have you ever experienced what it feels like to work on top of a roof with the shingles pouring off heat from the sun?  Good times.

Here’s where the antenna will be mounted.  I’ve picked a spot just behind the satellite dish because it offers a slightly lower tree-line to the north than at any other spot on the roof, plus that location will leave the bulk of the mount invisible from the main road and the front yard.

Finding the right location is important

Finding the right location is important

I kicked this part of the project off by determining the pitch angle of the peak so I can construct a sturdy base.  Since this project is low buck I didn’t use anything facy.  Just a piece of paper and sharpie marker that I traced the angles with.  When I was done it looked like a drawing of the Flux Capacitor.  You movie buffs won’t have to click the link to appreciate that one.

Using a couple pieces of scrap wood, I cut the angles with my trusty Black-n-Decker chop saw and did a test fitting.  I had to modify the angles just a bit, and keep cutting and fitting until I had it right.  it only took a couple of tries.  Once I had the correct angles, building the base was a piece of cake.

Angles are our friends (say 10 times fast)

Angles are our friends (say 10 times fast)

Now for the fun part.  On each side of the peak. just a few inches before the angle cuts join, I’m going to fit a couple pieces of 2×12’s and angle them up until they sit perfectly level.  These two pieces will form a 12″ rectangular hole that our 4×4 uprights will drop into.  These 4×4 uprights (which will be 6 feet long) will provide the pivot point and lower anchoring point for our mast. (Note the short 4×4’s at each end of the base.  These are extra pieces that I used to initially position the 2×12’s, and they will stay there to provide extra support although when we’re done they will not be visible).

Positioning the 2x12's was so easy! (not)

Positioning the 2x12's was so easy! (not)

Notice the orange level on top of one of the supporting 4×4’s?  You have to constantly check for level all the way through a project.  It’s a good rule of thumb to assume that every action you take will knock things out-of-level.  Since the main 4×4 uprights will anchor to the supporting 4×4’s, it stands to reason that if they are level and plumb, so will the main uprights.

My son James starting getting interested at this point and came up to help.

My partner in crime (and son) James III

My partner in crime (and son) James III

To further bulk up the base, we’ll add more (shorter) 4×4’s to the bottom of the base running perpindicular to the main uprights.  All of this framing will be hidden once we “skin” the top with a couple of pieces of 2X6, which will add even more structural strength.

At this point I’ve got the main 4x4x6′ uprights in place, and after going through my second battery on the cordless driver and about 100 3″ gold screws connecting everything together, those uprights are so secure I could probably climb them and sit on top.  Down in the base there are a total of 6 4×4’s interconnected with the 2×12 sides for stability.  At this point there are no entries into the roof.  Everything is self supporting, which is exactly what we wanted.  Now lets check for level again!

Checking the main uprights for level - Level is good!

Checking the main uprights for level - Level is good!

 Almost done for the day.  To finish, we’ll skin around the tops of the supporting 4×4’s to hide the framing and to make it all a little bit stronger.  This will hide the first foot and a half of the uprights, and bring our mast starting altitude to 18 feet.  I also closed the “top” parts of the rectangular hole around the uprights.  We’ll seal those up with silicone and then Thompson’s Waterseal the whole base to keep out the elements, but that will happen later.

Here’s a shot of the base before I skinned the top to hide the shorter 4×4 supports.

The uprights aren't crooked - I wobbled the camera.

The uprights aren't crooked - I wobbled the camera.

Next weekend, before we mount the mast, we’ll add some framing on each side of the 2×12 supports to hold some plywood that we’ll slope down to cover the open distance between the front of the ridgemount and the top of the upright supports.  With that in place we’ll add tar-paper, and then I’ll shingle it (the previous homeowner left boxes and boxes of shingles) so from the ground or the air it will resemble a section of pitched roof.

That’s all for today.  At the rate of progress I’m guessing we’ll go for an initial raising of the mast two weeks from today.  But maybe, just maybe, we’ll get to that next weekend- although I’m in no hurry.  After the work I did today I feel like an old man.  I sure wish I was still in my twenties. 🙂

To be continued…

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