-=> Quoting N3rr <=-
N3> Steel guy wires loosen up with age due to thermal
N3> expansion/contraction. They need to be adjusted (read: tightened)
N3> periodically, probably annually, if the environment produces
N3> winter/cold and summer/hot temperatures.
7-strand EHS should not stretch. Whether the guys need to be tightened
or not depends on their attachment method, doesn't it? If they're clamped
without serving the ends, then Rohn recommends a retightening schedule.
Use of Preforms or Nichro-press sleeves shouldn't require retightening.
N3> Many hams seem to prefer loose guy wires. I don't know why.
The purpose of the guy wires is to prevent the tower from falling over.
They translate lateral forces on the tower into compressive forces in the
tower legs. Tensioning the guys to 10% of yield strength or whatever preloads
the tower and reduces the amount of lateral load (antennas) the tower can
handle. Towers can also fail from twisting or torsion. Preloading the tower
should reduce its tendency to twist under load. I prefer to keep the guys
loose and use torque arms. With or without torque arms, guy brackets should
be used to attach the guy wires to the tower rather than wrapping them around
the tower legs to prevent stressing the welds. I'm not a mechanical engineer
either but this is MY interpretation of the literature! ;)
73 Bill, N6CQ/3
>From IK8JSV <gaetano.piscopo@pixel.stt.it> (Michele Piscopo) Sun Apr 28
>16:35:18 1996
From: IK8JSV <gaetano.piscopo@pixel.stt.it> (Michele Piscopo) (IK8JSV)
Subject: Antenna input sought
Message-ID: <v01530507ada92bbafc9b@[194.184.24.176]>
> I believe this was asked on the reflector a while back, but I
>never >saw many responses and did not get a summary, so here we go again.
>
> What do y'all think of putting a vertical antenna on top of a tower
>that has a tri-band beam presently installed. I am thinking possibly of a
>Butternut HF2 for 7 and 3.5 mhz. Mainly want to cover 7 mhz, but 3.5 would
>be a bonus. I mainly work the domestic contests and do get on and play in
>the occasional dx test as well.
>
> My main reason for wanting to try this is to get rid of some of the
>wire antennas that are hanging off the tower in various directions, and
>secondly to have a 7 mhz antenna that is fairly high above ground, with a
>full size radiator and a decent counterpoise.
I' m currently working on a antenna theory problem wich allows to evaluate
the effectiveness of an HF antenna as function of its height h over the
ground.
>From calculations I found that, assuming a moist soil, a vertical antenna
works quite well when h=0. The "real over ground average gain" decreases
when the antenna is raised up. When it is at 0.5 wavelenghts over the
ground it loses about 2.5 dB compared to the antenna placed at h=0. Rising
further on the antenna at more than 0.5 lambda its performances get better:
at 7 MHz,for h=1 wavelenght you will have the same "over ground average
gain" that you have at h=0 while at h=2 wavelenghts, you will have an
improvement of 4 dB. For bigger heights the o.g.a. gain decreases again.
I' m sending you, via a private E-mail, a graphic of the additional gain
due to ground presence, for a vertical and an horizontal antenna, as
function of h, ground quality ...
IF SOMEONE ELSE IS INTERESTED ON IT, CAN ASK ME it... I' ll send him a copy.
I' wouldn' t like to fill up the mailboxes of other people with big graphics...
So I don' t tink it' s a good idea to put your vertical on the top of the
tower (unless it' s more than 40m high): if you haven' t obstacles near
your site it will be better for you to put it at ground level (or just a
couple of meters over it, so you can put the radials distaced a couple of
meters from the ground in order to have negligible ground losses).
73,
Michele Piscopo, IK8JSV
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