EME Station 2.0 Part 9 – H-Frame Assembly

M2 Antennas 2X2 2MXP28-32 H-Frame

M2 Antennas 2X2 2MXP28-32 H-Frame

The final major component to be assembled is the 2MXP28-32-2X2-3K H-Frame which will support our four 2MXP28 Antennas. The H-Frame is one of the most mechanically complex components in our EME antenna system so we began by carefully studying M2’s manual for this component.

Parts Identification, Inventory, and Preparation

H-Frame Parts Inventory

H-Frame Parts Inventory

We also spent some time identifying and inventorying all of the parts. M2 supplied upgraded aluminum saddle clamps for our H-Frame. These parts improve the clamping action between the components and also reduce stresses on the fiberglass and other tube parts.

Truss Cable Parts Prep

Truss Cable Parts Prep

We spent some time preparing the parts for the Phillystran Truss cables for the Main Cross Boom and Vertical Risers. Prep included a drop of oil on each of the clamp threads and some NOALOX Antioxidant Compound on the turnbuckle threads. We also added stainless steel jam nuts to the turnbuckles to lock them in place after installation.

Initial Assembly of H-Frame Sections

Assembled H-Frame Sections

Assembled H-Frame Sections

We next mock-ed up the center section of the 3″ Main Cross Boom in the Elevation Rotator assembly to ensure proper fit and operation of the Elevation Rotator.

With this done, we assembled the Main Cross Boom, Vertical Risers, and T-Brace sections. This helped us to get all of the parts and hardware in the correct locations and to become familiar with how all of the parts fit together. We used a generous coat of NOALOX on all of the metal to metal tubing joints to facilitate the assembly and to prevent corrosion from forming at the joints of the metal tube sections. This sort of corrosion can cause increased noise levels after the array is installed outdoors for some time.

Main Crossboom Assembly

Cross Boom Truss Assembly

Cross Boom Truss Assembly

Next, the 3″ Main Cross Boom and its support Trusses were assembled. We carefully measured the assembly and marked the center as well as the locations of the Vertical Risers on the Main Cross Boom using a sharpie pen. these measurements will make the final assembly of the H-Frame on our Tower much easier.

Cross Boom Truss Details

Cross Boom Truss Details

The Phillystran Truss Cables and associated hardware were assembled and adjusted next.

Vertical Riser Assembly

Vertical Riser Mock-up

Vertical Riser Mock-up

We decided to Mock-up a section of the Vertical Riser center tubes and the associated Vertical Riser Truss supports on the Main Cross Boom. This allowed us to confirm that the final horizontal spacing of the Risers was correct and to get the clamps associated with this part of the H-Frame assembly properly oriented and squared.

Fiberglass Tubing Reinforcements

Reinforcement Bushing Design

Reinforcement Bushing Design

The Vertical Risers use fiberglass tubes at each end to provide a non-conductive mast for mounting the Antennas and their Truss Supports. The Antennas we are using are large and will need to be tightly clamped to ensure that they stay aligned and in place. The Antenna and associated Truss U-clamps put a great deal of stress on the fiberglass tubes and they can become distorted or damaged over time.

To prevent this, we decided to make a custom set of reinforcement bushings from polycarbonate plastic. Bushings were designed to reinforce all of the points on the fiberglass tubes of both Vertical Risers where U-Clamps will be used. You can see the full set of specifications for the bushings here.

W2SW Custom Reinforcement Bushings

W2SW Custom Reinforcement Bushings

Spencer, W2SW, owner, and founder of AntennaSys, Inc. made a beautiful set of custom bushings for us. Spencer has an amazing machine shop at his home and the parts turned out great and fitted precisely.

Reinforcement Bushing Installation

Reinforcement Bushing Installation

The reinforcement bushings were installed at the correct depth in each of the Fiberglass Tubes and are pinned in place using small stainless steel machine screws.

One consequence of installing the reinforcement bushings is that water can accumulate in the fiberglass tubes if they are in a horizontal position for a period of time. If such accumulated water freezes, it could cause damage to the tubes. This problem is easily solved by drilling a series of small 1/8-inch drain holes in the tubes on the bottom side when they are horizontal.

Assembled Vertical Riser

Assembled Vertical Riser

The final step was to assemble all of the parts associated with both Vertical Risers. The risers were marked to indicate the location of each Antenna Boom and Truss Clamp and the clamps were installed. The Phillystran Truss Cables were installed in the Eye Bolts on the Vertical Risers.

As we did with the Antenna Truss Cables, we will wait to install the turnbuckles until the Vertical Risers are installed on the tower and balanced. This will likely change the length of the Phillystran Truss cables.

Next Steps

The next step in our project will be the installation of our Elevation Rotator, H-Frame, Antennas, Power Dividers, MAP65 Housing, and Phasing Lines on our EME Tower. You can read more about our EME station project via the links that follow:

If you’d like to learn more about How To Get Started in EME, check out the Nashua Area Radio Society Teach Night on this topic. You can find the EME Tech Night here.

Fred, AB1OC

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One thought on “EME Station 2.0 Part 9 – H-Frame Assembly

  1. Great article on the H-Frame antenna and if I had a work shop like that with his knowledge I would try that. I love building antennas I like beams don’t have the room. I have learned a lot with these articles. Thanks much for sharing.
    73,
    Fred Jones WA4SWF

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