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MA-40 Antenna Tower Project

««« permit & foundation       «« tower install       « antenna install

Fall 2011: antennas, rotator, cables & lightning protection

The OptiBeam OB6-3M tribander is a Yagi on 10 and 15 meters but it's a Moxon on 20, making it possible for me to raise a beam with full-size elements in limited space. I find the look very clean and modern too. See my OB6-3M review on eHam.net.

OB6/3M on tower from yard

You might not notice the Diamond D220 2m-23cm mobile discone at the top if it weren't for the PVC pipe I used to mount it. Height matters: for local FM and D-STAR, even a J-pole would work great up there at 40+ feet! Here's my D220 review on eHam.net.

Below is a picture of both antennas riding the MA-40 tower up to full extension, as seen from the street:

OB6/3M on MA-40 from street

The tower is easily turned by a Yaesu G-1000DXA rotator. A medium-duty Yaesu G-800SA rotator was working fine the first year or two, but seems to have broken its limiter stop, although that may have more to do with Yaesu rotators' quality than this specific tower's weight. Others using Yaesu 800-series rotors with MA-40 towers have not reported problems, but I only noticed this issue myself when I upgraded to a Green Heron controller. The Green Heron needs to know exactly where that stop is.

The rotator is connected to the controller via landscaping wire that runs underground through a PVC conduit to the shack entrance. The coax cables are taped together as they come down the side of the tower through two standoffs. Those cables then loop around the base to allow for turning the tower, and disappear into a second underground PVC conduit. To avoid tight bends in the coax, I used a weatherhead cover on that pipe.

Yaesu G-800SA rotator and cable weatherhead

I later treated those rusty bolts in the base with Rustoleum, topped the bolts with plastic caps (from the ends of Cable X-perts coax assemblies), and had my general contractor seal up the gap between the base and the foundation pad with Quikrete per US Tower instructions. Note how it slopes away from the base:

MA-40-tower-base-concrete

The cables come out of a weatherhead on the other end too, and then connect to grounded lightning arrestors at the shack entrance. I hope to add pictures of my own, but meanwhile I borrowed the shot below (which is certainly a lot neater than my final results). Clicking on the photo below will take you to DX Engineering which sells that utility box and other grounding components including Polyphaser arrestors, but I also used some arrestors and copper ground bus bars from Alpha-Delta Communications.

Lightning protection gounding equipment enclosure

My radios are also grounded there, via a common point on my tuner, from which a flat braided ground strap leaves the shack. Everything at the shack entrance is connected to an 8' buried ground rod, which is in turn connected to all other grounding points around the house, including the tower, as I'll explain next.

As you may recall from the foundation installation page, the tower base bolts are grounded inside the concrete to the foundation rebar and to another ground rod. All ground rods around the house are connected to each other by buried #10 wire, which terminates in a Ufer connection to the house foundation rebar. If you don't know anything about this - and even if your electrician says he does - it's worth investing in a copy of the National Fire Protection Association (NFPA) recommendations on lightning protection. They sell a protected PDF of that online.

All cables enter the house through a couple of 4" wide 3M Fire Barrier Pass-Through Devices, a neat little invention my electrician found at his electrical suppliers. I later stuffed insulation inside.

3M cable pass-thrus

I hope this has been useful information for anyone considering one of these towers! See also my eHam review of the MA-40

««« permit & foundation       «« tower install       « antenna install

1) Permit approval, concrete foundation
Page 2: assembling tower
2) Tower delivery and assembly
Page 2: assembling tower
3) Mounting beam antenna on tower
Mounting the beam

Other projects:

Antenna Farm 3: The Slanted Roof Solution
Antenna tripods over slanted roof

...and:

Antenna Farm 2: The Flat Roof Challenge
Flagpole Antenna Project • Antenna Farm 1
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