Antennas On The Tower – Part 1 (Preparation And Upper Yagis)


Antenna and Tower at Night

Antenna Stack And Tower At Night

As I sit here writing this blog post at the end of the second day of work to install antennas on our new tower, I can reflect back on some pretty memorable experiences. I have certainly learned a great deal during the last few days.

The work began this past weekend with the final assembly and test of our 2m and 70cm beams. Both beams use mast mounted boom truss plates and I wanted to fully assemble these ahead of the installation on the tower to set the boom support lines to the proper length and give them a chance to stretch a bit. To do this, we made a set of 10 ft test masts from some PVC electrical conduit. Shown here is our M2 2M18XXX 2m beam installed on the 3″ test mast. We also installed a short length of coax on the 2m beam so that we could check the antenna’s SWR performance prior to installation on the tower.

2M Yagi Test

2M Yagi Test

Our M2 440-21ATV 70cm beam has a 14 1/2 ft boom and did not come with a boom support truss. I am using LMR600 UltraFlex coax for the rotator loop and feedline connection to this antenna. LMR600 UltraFlex coax has a good deal weight to it. To prevent the boom from sagging due to the weight of the coax, M2 Systems provided us with a custom boom truss setup which is shown installed on the test mast. This should improve the reliability of this antenna and was easy to install. I also installed jam nuts on the boom truss turnbuckles for the 70cm and 2m antennas to prevent them from coming loose once the they are on the tower.

70cm Yagi Boom Truss

70cm Yagi Boom Truss

With this work done, we were ready for Matt and Andrew at XX Towers. They arrived on Monday morning and began by prepping the 70cm and 2m beams for installation on the tower. I made up feedline extensions to go from the M2 Pre-amp Systems for these antennas on the tower to the antennas. I made up the extensions using LMR600 UltraFlex cable for the 70cm beam and LMR400 UltraFlex cable for the 2m beam, both with crimp-on N-connectors.  We are using a 2″ insulated mast extension (from M2 Systems) so that the 70cm beam does not “see” the mast which would adversely effect the antenna’s pattern. The 70cm beam is shown below installed on the fiberglass mast extension which is about 5 ft long. Matt attached the 70cm antenna, boom truss and feedline to the mast extension on the ground to minimize the work required on the tower. He also attached the feedline to the 2m beam on the ground.

70cm Beam Prep

70cm Beam Prep

Finally, noting the rubber element boots on the SteppIR antennas are prone to UV damage, Andrew covered all of the boots on our SteppIR DB36’s with a layer of electrical tape to give them some additional UV protection and extend their life.

SteppIR DB36 Final Prep

SteppIR DB36 Final Prep

With all of the prep work done, it was time  to start the installation of antennas on the tower. The first step was to pull the 3″ steel mast up the tower and clamp it inside the mast thrust bearing in preparation for the 70cm beam installation.

Mast Going Up The Tower

Mast Going Up The Tower

Next, the 70 cm beam and mast extension went up the tower and were installed on the mast.  The total length of the mast above the tower plus the extension will be about 20 ft. This will leave about 5-6 ft of the 3″ steel mast inside the tower which is just about right. After consulting with Jason at M2 Systems, we settled on the spacing between the three antennas on the mast – 6 ft between the 70cm and 2m beams and 10 ft between the 2m beam and the SteppIR DB36 which will be just above the top of the tower. This put the installed heights of the antennas at 118 ft (70cm yagi), 112 ft (2m yagi) and 101 ft for the SteppIR DB36 yagi.

70cm Beam Up The Tower

70cm Beam Going Up The Tower

After the 70cm beam was installed, Andrew pushed the mast up a few feet to prepare for the installation of the 2m beam and we hauled the 2m beam up the tower reflector end first.

2M Beam Up The Tower

2M Beam Going Up The Tower

Shown here are the 2m and 70cm beams fully installed on the mast. The 2m antenna has a 36 ft boom but it looks quite small at 100+ ft!

VHF-UHF Beams On Mast

2m And 70cm Beams On The Tower

We choose an M2 OR2800PXAZ prop pitch style rotator to turn the upper three antennas on our tower. This heavy-duty unit was a good choice given the size and weight of the SteppIR DB36 yagi that it will be turning. Next up the tower was the rotator and associated base plate. With this installed, the mast was pushed fully up in preparation for the installation of the SteppIR DB36.

M2 Rotator

M2 Rotator

The DB36 is a big antenna and it weights about 165 lbs fully assembled. The best way to get it onto the mast at our site was via a tram line system. With the tram line cable rigged to the mast and a tree in the woods next to our yard, we attached the DB36 to it via a pulley and some cable clamps to anchor the pulley on the tram line. Matt then used a pair of come-a-longs to take the slack out of the tram line which lifted the DB36 off the ground. We then looped a light guide line around the end of one of the elements so that we could steer the DB36 as it went up the tower.

SteppIR DB36 on Tram Line

SteppIR DB36 Suspended On Tram Line

The next picture shows the DB36 about half way up the tower. Note that we removed two of the three sets of top guys from the tower prior to this step to avoid the DB36’s elements entangling in the upper guy wires.

SteppIR DB36 Up The Tower On Tram Line

SteppIR DB36 Up The Tower On Tram Line

Once we had the DB36 fully up the tram line, Andrew attached it to the mast. All in all, the tram line system worked very well. It was an awesome experience to use this approach to lift such a large antenna into place!

SteppIR DB36 Installation on Mast

SteppIR DB36 Installation On Mast

With the three beams on the tower, the next order of business was to install the hard-line coax feedlines on the tower. We are installing a total of five hard-lines on our tower:

  • A run of 1 5/8″ hard-line for the 70cm beam
  • A run of 1 1/4″ hard-line for the 2m beam
  • Two runs of 7/8′ hard-line for the two SteppIR DB36 beams
  • A run of 1/2″ hard-line for the planned 80m and 160m wire antennas

The reels of hard-line coax are shown below.

Hardlines

Hard-lines

Unfortunately a business trip prevented me from being at home to help Matt and Andrew on the second day of the installation. They made a great deal of progress as you can see from the pictures below. They installed the K0XG ring rotator at the 60 ft level. The ring will turn the second of the two SteppIR DB36’s that will go on the tower. They also installed all of the tower mounted electronics and switches. These are shown in the picture below – the items from top to bottom include: the M2 2m and 70 cm tower mounted pre-amp systems, a DX Engineering Broadband Stack Match System and our Custom Feedline Break-out System (both installed at 80 ft, the smaller light-colored box on the left is the feedline break-out), the K0XG ring rotator, and finally our previously installed Davis Wireless Weather Station at the bottom right. The K0XG Ring is a 115 VAC powered heavy-duty until that is extremely well-built. It should do a great job of rotating our lower SteppIR DB36 around the tower. You can also see four of the five hard-line cables in the picture.

K0XG Ring Rotator at 60 ft

K0XG Ring Rotator At 60 ft

The devices installed at the base of the tower include the control box for the K0XG Ring (left) and a DX Engineering Remote 8 Port Antenna Switch for the wire antennas (right).

Electronics at Tower Base

Electronics At Tower Base

I now need to build several sets of LMR400 UltraFlex cables to connect the hard-lines and antennas to all of the electronics. Each of these cables will be tested with a dummy load and an antenna analyzer to ensure that they perform correctly before they go on the tower. The cables that run between the Stack Match, Feedline Break-out and the two SteppIR DB36’s must be built identically to ensure the best performance from the array of the two SteppIR’s. All of this is going to take a couple of evenings to complete. Matt and Andrew will be back later in the week to complete the installation of the feedlines and control cables.

– Fred (AB1OC)

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