Heavy duty military mast placement

I have been planning to put up a directional multiband HF antenna like a hex beam or cubical quad for the past year. Having calculated the expected wind load and desired weight of the antenna, I realized that my current alu-telescopic mast would not handle the size of the antenna and a rotor. I started to look for a solution – some kind of heavy-duty telescopic or crankable mast. Having considered the measurements of my property, I have decided to look for telescopic masts only. I was looking for demobilized military masts because they are famous for their reliability and endurance. I had two options – a 12m pneumatic mobile telescopic mast or a 16/20m pulley-type heavy-duty mast. The final decision was made because of the max height and self-resistance to rotation around the mast axis – pneumatic masts do not have guides that prevent segments from rotation – I was afraid that a rotor would rotate the mast segment, not the antenna. In the end, I bought a 16m pulley-type military mast demobilized in the past century from CCCP.

When I bought the mast and it arrived at my location in Cracow I find out that it needs some refurbishment. The body was dilapidated and the bottom part rusted. I started with dismounting and cleaning the pulley system from the old grease. At the same time, I inspected the steel cords – surprisingly they appeared to be in a very good shape – no rust at all. I assume that they had been replaced just before the mast was demobilized and stored in the army warehouse. The next step was to put all parts together. In the end, the mast has been painted with military-olive colored anti-corrosive maritime boat paint.

Mast before and after the refurbishment

Just after refurbishment completion, I bought a 3.2m long steel rail-channel bar, because the mast is not able to stand itself without any support. The mast is 2.7m long in a folded position, while the base section is 2m long including the first pulley segment, so the first tube section is around 1.8m long. This means that the mast can be attached to max. 1.8m of the channel bar to keep it nicely supported. Having considered the above, I decided to plan the ground-above section of the channel bar to be 1.5m long, so the underground section was finally 1.7m long. The next step was to prepare a mounting surface for the channel bar – I gave up the idea to make a foundation – I decided to use an underground part of a 60cm wide heavy-reinforced retaining wall. I prepared the ground hole by the wall deep for 2 meters. At the very beginning, I made a 30cm concrete base at the bottom of the hole – under the desired position of the channel bar. The next step was to measure the channel bar position and drill holes for 14mm stainless steel anchor bolts in the retaining wall. The anchor bolts have been installed in the wall using the epoxy mixture. Afterward, the channel bar has been leveled in a proper way, secured with double stainless steel nuts and finally secured to the retaining wall.

When the channel bar was finally secured, I started preparations for the mast attachment – mounting bolts, clamping rings, XPS base plate and rubber pads. The next step required a hand – raising and securing the mast to the channel bar was a serious challenge. The mast weighs 100kg so it requires at least two strong men to raise it to the standing position and manipulate it. Thanks to my friend Michal who helped me during this step, the mast has been leveled and secured with an iron band and 8mm screws. The mast is isolated from the channel bar with rubber pads to not pass the wind vibrations to the channel bar. It also stays on the XPS base to not touch the ground directly.

The mast deployed to its half-height

The channel bar and mast have been grounded to the iron strap system which was arranged during the hole digging process. Iron straps are placed 3m below the channel bar bottom tip, so they are around 5m deep in the ground. Straps are bonded together just below the mast base and one of them is finally connected to the mast pulley enclosure. Also, the telescopic part of the mast and channel bar is bonded to the same point. It should ensure the same potential at all parts of the mast installation.

The mast is reliable enough to be raised to its half-height without a guy system with an antenna on top but to ensure that the whole construction will be wind resistant and steady for a long time period, the guy system is necessary. I decided to use the military guy system which consists of a 3mm steel cord separated into short segments with ceramic isolators to prevent the anchors from ham band interactions. Mast segments are equipped with guides, but to ensure that the top section will not rotate in the lower one, I decided to add a mast jumper at the top and to equip the guy mounting socket with steel angle bars as extensions 30cm long. Extensions and the mast jumper will provide better resistance to the top section rotation during strong winds or when the rotor will be used.

The mast can be easily folded from 13m height to 2.7m (transport position) in less than 2 minutes (I’ve measured 1min39sec in a hurry). It’s very functional in terms of storms and strong wind forecasts. Folding requires only one person.
Deploying the mast takes in total around 20 minutes – 4-5 minutes for deployment and 25 more for guy system arrangement (to level the mast correctly). Deploying is possible for one person, but completing the process in a group of 2-3 people takes max 10mins and is way safer (continuous guy system tension control during the deployment).

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