[TowerTalk] Questions on tower guying, brackets, etc.

[n4kg@juno.com]

N4KG responses intersperced below.  Caution:  
Examples are a violation of the K7LXC "prime directive".

On Fri, 11 Aug 2000 Nat Davis <ndavis@vt.edu> writes:
> 
> I want to add another tower section to bring the overall tower 
> height to  40'.  I can not go any higher than 40' on my small 
> house lot without  violating zoning setback requirements...  
> With a modest mast, my  antenna  (hoping to upgrade to a 
> Force 12 C3S or C4S) will be some 45' off  the ground.

	Good choice.  40 to 50 ft works VERY WELL on
	the high bands, especially during daytime and
	high sunspot activity.  N4KG
	
> After reviewing the self-supporting and bracketed tower 
> information  in the Rohn catalog, I feel that I must add 
> guy wires to the top of the  tower --  25' of tower above 
> the bracket is just a little wobbly for my taste  and 
> antenna wind load (am in a county rated at 70 MPH). 
>  Here is where I  need  your collective opinions:

	Yep, one set of guys on a 40 ft tower is
	highly recommended.   N4KG
> 
> 1.	In the past, Rohn has described attaching guy wires 
> directly to/around  tower legs at the cross bracing joints. 
> Rohn has dropped this method  from  their current catalog, 
> however.  The ARRL antenna book still shows  this as 
> a way to attach guys.  For my tower size and configuration, 
> would  this work  OK or should I spend the $$ and use the 
> guy bracket assembly?

	NO Problem (IMHO).  As I have previously reported,
	the guys on my 130 ft R35 tower are connected to
	the tower legs by looping the guy grips through the
	corners of the Z braces, around the tower legs.
	The top set of guys (1/4 inch) held up two trees
	which fell on them during a small tornado. NO
	damage to the tower.  N4KG

> 2.	Guy anchors:  I would prefer to use screw-in anchors 
> (vs.  buried  concrete anchors) and I have seen lots of discussion 
> on them (pro and con)  in the archives.  The "stock" Rohn anchors 
> seem too weak with their 2,500  pound pullout rating.  From the 
> AB Chance product line, I was  considering  their model 6346 -- 
> 66" long with 6" screw and galvanized.  It has a  pullout rating 
> of 4,500 pounds -- more than the breaking strength of  the 
> 3/16 EHS.  These anchors are a little more than 2x the price of the 
> model  604s that are only 48" long, do not appear to be galvanized, 
> and  have a  pullout rating of 4,000 pounds.   Does anyone have 
> experience with  either  model or can suggest others?  
>Are the 6346s overkill?  Would the  604s be OK 
> for my installation?  If they are not galvanized, should I be 
> worried about  them "rusting away to nothing" over time?

	My short towers are guyed to 4 ft anchors with 4 inch
	plates.  Both survived estimated 90 mph winds from
	a small tornado.  This includes a 40 ft tower with TH7
	and a 55 ft tower with 5L10's at 62 / 32 ft and 4L15 at
	55 ft.  GALVANIZED is definitely to be preferred. 
	A 6 inch plate is a bonus.  N4KG

> 
> 3.	Just looked at my ruler and 3/16" diameter cable looks 
> darned small  !!!!!  :-)

	Rated strength for 3/16 inch EHS is 4000 lbs.
	Rated strength for 3/16 inch HS is 2500 lbs.

	The horizontal force of an 86.6 MPH wind is 30 lbs/sq.ft.
	A 10 sq ft antenna would present a 300 lb load to the top
	of the tower.  This force must be offset by the horizontal
	component of the guy wire tension.  For guy spacing of
	only 50%, the guy tension will be 2X the horizontal load
	or 600 lbs., well UNDER the rated strength of any 3/16
	inch cable.  I have used 1/8 inch guys on short towers
	in the past but they rust out in 10 years.  GOOD 3/16
	inch cable should last at least 20 years. (Purists will
	want to add 30 psf times 2 sq ft / 10 ft tower section
	spread over the top guy and bracket).

	Bottom Line:  IMHO, a single set of 3/16 inch galvanized
	guy wires attached to a 4 ft screw anchor will make a 
	VERY SAFE and secure 40 ft. installation that should
	last for several decades.  N4KG
	> 
> Thanks for any suggestions you can give me.
> 
> Nat Davis
> N4EL
> 

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