I'm assuming that your Mosley CL-36 wasn't the antenna that was installed on
the Rohn HDBX48 tower. I also have an HDBX48 tower, and if I remember correctly
without digging out my Rohn catalog, the antenna installed on an HDBX is
limited to a maximum boom length of 10 feet, and maybe something like 10 sq.
feet of wind load.
To get a tower permit for for my HDBX48, I had to be sure not to exceed the
published antenna limits of the tower. That meant that even antennas like a
typical 3-element triband yagi (TA-33, Hy-Gain TH-3 series, etc.) wouldn't
work. Only antennas like a 2-element TA-32, TH-2 series, or a 2-element Quad
would qualify with the boom length limitations.
I went with a 2-element 6-band quad. The tower was up for about 15 years and
never flinched even in the big wind storms.
LJ
-----Original Message-----
>From: Nick Pair <daweezil2003@yahoo.com>
>Sent: May 14, 2007 11:06 AM
>To: towertalk@contesting.com
>Subject: [TowerTalk] Rohn HDBX and Mosely
>
>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.
> Nick
> WB7PEK
> Dodging lightning somewhere on a hilltop in SW WA
>
>
>
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