[TowerTalk] sag--->length in guy wires

[k6ll@juno.com]

On Thu, 15 Jun 2000 20:51:33 +0000 Pete Smith <n4zr@contesting.com>
writes:
> 
> Is there a good rule of thumb for how much additional length is 
> required in
> 3/16 EHS to account for sag, as compared with the pure mathematical 
> right
> triangle length?  Put another way, if a guy station is at 95 feet 
> above
> ground, and the guy anchor is 85 feet from the tower base, 
> Pythagoras says
> the guy is 127.5 feet long.  How much should you add in length to be 
> safe
> when pre-cutting guys?

For horizontal wires, there is a nomograph in the ARRL Antenna
Book that will give you sag as a function of span (1/2 the
distance between the supports), tension, and
wire weight.

For vertical wires, there is no sag.

I would take the horizontal nomograph sag and multiply it by the
cosine of the guy elevation angle, with 90 degrees being straight
up.

For your example:
span = 63.75 feet
tension = 400 pounds
wire weight = 73 pounds per 1000 feet
cosine of the guy angle = .67 (85/127.5)

Nomograph sag for horizontal wire =  0.4 foot
Nomograph sag x cosine of guy angle = .27 foot (.4 x .67), or about
3.25 inches.

The nomograph in the antenna book is not optimized for short spans
and high tensions, so the sag scale goes from 0.5 feet to 50 feet.
I had to extrapolate a little to get to the 0.4 reading.

Caution! This mechanical engineering data was generated by an
Electrical Engineer.

Dave Hachadorian, K6LL
Yuma, AZ
K6LL@juno.com

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