In a message dated 1/18/01 8:53:06 AM Pacific Standard Time,
jskatz@sk.sympatico.ca writes:
> My plan is to put a Force 12 C31XR and a EF-240s on top of a 58 foot
> foldover 25G.
>
> I am using 70 mph as my design speed.
>
> The Rohn table indicates that 60' 25G tower with two sets of three guys
> attached at the 28' and 55' points and a guying radius of 48' can a handle
> a top round load of 16.8 sq ft at 70 mph - no ice (we rarely get icing
> here - it is too cold :-). The total area of the Force 12 antennas is 13.6
> sq ft. My calculations indicate that if I place the C31XR at the top of the
> tower and the EF-240s 10 ft above that I will add about 1 sq ft of mast
area
> and I will need a mast with a yield strength of about 40,000 psi. Good mast
> materials are hard to find in this area but I might be able to locate some
> 42,000 psi stainless steel. Barring that I will have to reduce the
> separation between the two antennas to 9 ft and use 6061 schedule 40
> aluminum with a yield strength of 35,000 psi.
>
The MARC (Mast, Antenna and Rotator Calculator) Program shows that either
will work FB. (Available from <A HREF="www.championradio.com">
www.championradio.com</A> )
> My rotator is a T2X that will be mounted as far down the tower as possible
-
> likely within 10 ft of the base of the tower. I have a thrust bearing at
the
> top of the tower and I am going to place another bearing about 10 ft below
> the top of the tower. I have not quite decided how to handle the coupling
> between the 18 - 20' top mast section and the lower section which will run
> down the center of the tower to the rotator. Also, I have not decided what
> type of material I need for lower section of the mast.
I'd skip the second bearing - too easy to introduce excessive bind into
the system. Having another AS (accesory shelf) will suffice to capture the
mast.
Coupling two pipes isn't easy. If you drill them both and pin them to
each other, eventually the holes will elongate and/or the bolts will shear.
The lower mast can be anything since it won't be taking any side load - even
Schedule 40 water pipe.
Cheers, Steve K7LXC
Tower Tech
Champion Radio Products
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