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[TowerTalk] MARC question

To: <>
Subject: [TowerTalk] MARC question
From: (
Date: Sat, 31 May 1997 09:30:09 -0400 (EDT)
In a message dated 97-05-31 01:41:08 EDT, you write:

> I assume antennas can be added to the database by simply editing the
>  antennas.dat file with any text editor.  Is this correct?

    You could be correct. I'm not the software author and really don't know
anything about the software mechanics so I can't give you a definitive
answer. How about a "definite maybe"?
>  Second question.  I already own a US Tower mast, their # M-20R.  You 
> probably
>  already know this, but it is a 20' Galv. steel mast, 2" OD, .120 wall with

> an
>  insert in the lower half, giving the lower half a .250 wall thickness.  
> Weighs
>  70 lbs.  Any suggestions on fitting this into the results I get from the 
> MARC? 
>  I don't see any info. in their catalog on yeild strength, but as it is 2"
>  tube with the listed wall thicknesses I would think it is more than just 
> galv.
>  pipe.  I have a call in to UST to try to get more info, but perhaps you 
> already
>  know what it is.

     I don't have any idea what the US Tower mast pedigree might be. Yes,
you'd have to give them a call and see if they know. Maybe they do and maybe
they don't. As long as that spec meets the MARC recommendation, everything
should be FB.
>  Where I would like to use it is on top of a rotating tower (MA-550MDP with
>  freestanding rotor base).  It would only go approx. one foot into the
>  leaving 19 ft. of useful mast above it.  I would like to install a TH-7DX
>  the mid point of the mast (or higher) and a small antenna at the top, a 
> decent
>  TV antenna so I can tell the cable company to kiss off (any TV antenna
>  recommendations?).
     Sorry, HF antennas only. 

     I'll bet you a nickel that your proposed mast installation is NOT
recommended by the manufacturer.  Even if the tower could take that BIG
bending moment (and I don't think it will), I don't think that your 1 foot
and 19 feet mast proportions are appropriate - or safe.  

     This is a lightweight tower. It's only rated at 10 sq.ft @ 50 MPH.
Contra Costa county is a 70 MPH wind zone. That means at 70 MPH the tower
capacity is about 2.5 sq.ft. or thereabouts. The 19 feet of mast alone is
almost 2.2 sq.ft. just by itself. I'd be very careful with this tower.

>  Actually, I suspect this should be plenty strong (I'm in a very sheltered
>  location and this tower is motorized so it is down any time the wind is 
> blowing
>  or we are away.)  However, what concerns me more is the ability of the
> to
>  support the antennas and itself while it is being tilted up from the
>  horizontal, the ability of the top of the tower to support it (it actually

> goes
>  less than a foot into the tower) and the ability of the raising fixture
>  Tower MAF-550) to support the extra load of the mast and antennas during
>  raising process.  I can help it along for the first few degrees of
>  (where the angle is the worst) but it soon gets out of reach.  I'm hoping
>  avoid the necessity of erecting a temporary tower behind it to use as an
>  assistant raising fixture for the mast.   I have a similar question about
>  tilting up another stack, but I'll save that for later.

    Again, I doubt that the factory will give you the green light on your
proposed installation. I'm sure that the increased weight and drastically
different geometry will far EXCEED the safe working capacity of the raising
fixture and whole system. 
>  I should also mention that I have an elevation rotor, crossboom and 
> satellite
>  antennas monuted down low on the tower (on the lowest, outermost section
>  tube).  These are quite small, but I mention it because I'm frequently
>  experimenting and playing with them which requires tilting the tower over.
> I
>  really don't want to have to rent a crane every time I do it.
     You're correct to be concerned about the ability of the hardware to
handle your proposed configuration. Don't forget that with your 19 foot mast,
you're almost doubling the total length of the tower. That has drastic
implications on EVERYTHING. All of the forces will at least double and
probably more. I'd see what the factory says and modify your plans to
something not quite so aggressive.

73,  Steve  K7LXC

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