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[TowerTalk] Rohn HDBX and Mosely

Subject: [TowerTalk] Rohn HDBX and Mosely
From: Nick Pair <>
Date: Mon, 14 May 2007 11:06:53 -0700 (PDT)
List-post: <>
I would just like to relate a story on the HDBX 48 that I have had up for about 
20 years. The tower was OK for the first 15 years or so, with a little rust 
showing up around the 10Th year. The bolts that join the sections together were 
the first to rust, with a little rust showing up on the edges of the X's and 
the vertical rails(all of which were sheared and formed after galvanizing). At 
the 15th year I noticed in that winter that the tower top was moving in the 
heavy winds a lot more than I remembered. Next big wind storm I b raves the 
storm to go out and watch the tower react to the gusts. I discovered that the 
tower was lose between sections 2 and 3. I had installed all bolts according to 
Rohn's directions and even used a torque wrench to verify tightness. After wind 
died down I was able to climb tower and found out that the bolt holes on two 
sides had elongated by almost a quarter inch and that the third side had the 
section of the leg below the second had completely
 broken off from the midpoint of the bolt down. So all I could think of to do 
was to place a guy wire (using a cable with a hook on the end of it so I didn't 
have to climb beyond the break) on the top of the next section and apply enough 
force to keep the tower from rocking and doing more damage. Now I have a 
useless tower that I can't get down with a gin pole and I can't think of a way 
to get it down besides just cutting it loose and toppling down. That would 
destroy antenna and with my luck the rotor too. I might be able to erect a 25g 
tower with temporary guys to use as a tower crane. Access with a real crane 
truck is difficult and not within my ham budget at this time. As to the 
aluminum rivets I was very surprised when I got the tower here and found 
dissimilar metals on it. I am still surprised to find that they have not been a 
source of rust over the almost 20 years I have had the tower. They must be of a 
alloy that I have not heard about, or they might be mixing
 aluminum with the zink they galvanize with.
   Now about the Mosley antennas, I have not had the TA versions but have had 
the CL-36's for almost thirty years and other than needing a boom truss system 
added for my higher than normal wind location and a little more drupe on the 
elements than other brands, they have preformed well and been mechanically 
secure all the while. The other fellow that mentioned that the driver seemed 
longer that the reflector is due to the feed system they use. Their patented 
balanced feed is a version of the T match that uses a made up series capacitor 
to feed each side of the insulated split driven element. The capacitor consists 
of a length of 15 kv rated wire inside of the element halves tied to the center 
of the feed connector. Its this series capacitor that necessitates a longer 
than quarter wave element halves to get back to resonance.(forming a electrical 
1/4 length) While this capacitor value is a compromise for triband use, it sure 
makes a clean looking installation with all the
 components inside the element away from the weather. I'm not trying to say 
this antenna is better than monobanders of the same length, but it is a good 
balance of the compromises one has to make with a tribander.(and maybe a better 
balance that they were able to achieve with the more modern designs they are 
selling now!)(all those duel drivers and the phasing lines are not enough 
improvement to justify their complexity and weather survivability. 
    Dodging lightning somewhere on a hilltop in SW WA

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