Antenna height is an important factor for HF contacts. There are new antenna masts on the market and exceptionally a used mast will also appear in the auction. One such model is RDM-12 antenna mast. RDM-12 was a military mobile station on a Praga V3S truck. The mast was transported on the roof of the V3S in the folded state. The extension is performed by a crank by means of mechanical gears.
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Initial condition of RDM-12
I managed to buy a mast in December 2019, including the upper part with rotator and bearing. Corrosion was visible on the surface, but mechanically it was fine. The mast then waited until the summer for the restoration to begin. Before I started, I read the available information from the web OM7KW a OK5AJA. Steve OM7KW sanded the mast by hand for a week. That's why I fitted the angle grinder with a grinding wheel and a prerequisite head, that in a day I will have to grind it.
Sanding and painting RDM-12
However, the reality is this, that only the outer surface of the pipes can be ground in this way, but it is no longer possible to get into the internal structure with the grinding wheel. She got there steel brush in the scorching sun a lifeless three-day robot.
Painting is only a little easier than sanding. Base color I applied by spraying. Top (two) the layers were painted with a corner brush. Unlike the original color, I chose a shade called. blacksmith black. All these works took a total of about 40 hours.
Excavation work and anchoring of the RDM-12 mast
The base of the mast was planned approximately in the middle of the plot with anchorage at the boundary of the plot. Although it would be appropriate, that the anchor ropes extend directly from the ground foundation, for the comfort of movement in the garden. The mini excavator therefore dug four pits in the corners of the plot and one in the middle. Thick-walled profiles came into the corner pits 60 x 60 mm with a length of 3m. In the autumn, I managed to paint and concrete only two profiles. They are sunk into the ground to a depth of about 1,1 meters. The concrete was cut in a furrow. These works took about 10 hours.
The first spring work and tips for mast heels
As soon as the spring weather allowed, I concreted the remaining two profiles. The inside of the profiles was filled with dry concrete. If water enters the profile, which freezes, it also means the destruction of the solid profile and the concrete foundation. Thus, dry concrete does not serve to strengthen after hardening, but to fill the inside. This part of the work also took about 10 hours.
Supporting structure, winch – hoist
I was inspired by the knowledge of OM7KW about the so-called. hoist. From two thick-walled profiles 60 x 60 mm with length 4 meters was created support structure including Strend Pro HW-100-800 winch. It also required drilling with large drill bits, which was quite physically demanding. Hand drill, which I had available was not the most suitable and of the three HSS drills (lower quality) I also destroyed. Then the structure was sprayed with primer and again with two coats of topcoat. I installed the lift in about one meter of cubic concrete. A part of the installation is also a tube, into which the RDM-12 mast with a joint is inserted. It is also equipped ground pin. The work could take about 15 hours.
It remained to be prepared upper part of the mast with rotator. He needed to be repaired, but relatively simple. Of course, this part of the mast was also sanded and painted like the other parts. It worked 5 hours.
I did not want to underestimate the choice of mooring ropes. After long searches on the internet, I opted for material from DX Avenue . Not only that, but also clamps. Everything is very well illustrated on their website and it is a good inspiration for what correct anchoring it will be necessary (eye sockets, clamps, turnbuckles). Ide o Deltex rope, which, especially in the long run, should be of better quality than commonly used anchor ropes. Deltex is extremely firm to the feel, but also a little stubborn rope. The choice of ropes and accessories took perhaps 3 hours.
This made it possible to lift the RDM-12 mast and prepare the anchorage. It is easier to lift an empty mast and measure the anchorage than to lift a loaded mast. All the more so, that I carried out all the work in one person. When lifting the mast, I helped myself with a base made of concrete blocks and foundation of a ladder.. However, the extension of the mast showed one planning error. The crank to the lifting mechanism cannot be fitted for a reason, that it is blocked by a hoist. I had to use ordinary socket wrenches and extend the mast bit by bit and then anchor. This part of the work was physically and time consuming. There are a number of nuts on the anchor ropes. But better than regret it later. All this work took about another 10 hours.
This was followed by the lowering of the mast. It will be at the top of the mast moxon tribander and lower arm with pulley, which allows you to quickly get wire antennas into the air. Preparatory work, thus mounting the antenna, cable and the preparation of anchor ropes took about 4 hours.
The final extension of the mast followed. Weight of the upper part, rotator and antenna is already noticeable. The ejection took about 3 hours.
In summary, therefore, the work on the mast represents 100 hours. This is a considerable volume. This blurs the advantage between such an overhaul of an older mast and the purchase of a new mast. The new part of the lattice mast is coming out approximately 100 € / meter, but the mast would not be extendable and tiltable. RDM-12 is one of the older military constructions of excellent quality and will serve for amateur radio purposes.