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G8MNY > TECH 20.03.09 11:37l 216 Lines 10901 Bytes #999 (0) @ WW
BID : 20965_GB7CIP
Read: GUEST
Subj: Wall & Chimney Brackets
Path: IZ3LSV<IK2XDE<DB0RES<DK0WUE<7M3TJZ<HG8LXL<XE1FH<ED1ZAC<GB7CIP
Sent: 090320/0101Z @:GB7CIP.#32.GBR.EU #:20965 [Caterham] $:20965_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
By G8MNY (Corrections Dec 08)
(8 Bit ASCII Graphics use code page 437 or 850
Some thought must go into mounting aerial poles to a building. Will it be
strong enough for what you want to put in it, will it overload the wall or
chimney & damage it?
T & K BRACKETS ³ ³
Ideally the K should be the top \ ³ ³
bracket as it is on the weaker \ ³ ³
top section of the wall as it has \ ³ ³
more bolts to spread out the load. Roof\ ³ ³
But only the K bracket can take \ ³ ³Aerial
down loads, if downloads are put ³\__/³ ³Pole
on the T bracket it will bend or ---ÚÄÄÄÄÄÄÙ ³ ³
leaver the bolts out of the wall! ³ Gutter³ ³
Two K brackets would be better. W ³___________³_³__
³³]Bolt o o ³ T bracket
So it is normal to put the K at ³ÁÄÄÄÄÄÄÄÄÄÄÂÄÂÄÄÙ
the bottom, where it's download A ³ ³ ³
ability is best utilised. ³ ³ ³
(U can stand on it!) ³ ³ ³
L ³ ³ ³
If you mount either type too high ³___________³_³__
there is not enough rows of bricks ³³]Bolt o o ³ K bracket
above it, so it could pull the wall L ³ÁÂÄÄÄÄÄÄÄÄÄÂÄÂÄÄÙ
down etc, if the cement is poor ³ ³ // ÀÄÙ
(old sand only between bricks). ³ ³ //
As far as the pole & bracket forces ³ ³ //
go, the further apart they are ³ ³ //
the better. ³ ³//
So you have to make a compromise, ³]³/
deciding how strong the wall is at ÃÄÙBolt
the top to determine the max bracket ³
height & how much of the pole needs ³
support, below that. ³
Always use the centre of bricks (if visible) for expansion bolts. Pre-mark the
wall & use a hammer drill etc. When fixing the bracket do up the bolts very
tight, but not enough to crack the brick! (depends on luck mainly!) If you have
cracked a brick or have a poor hole, move the bracket a row of bricks or
sideways if possible. If in doubt drill out the bracket to take more bolts.
It is always wise to check the bolt tightness at the next maintenance check!
If you have to remove wall bolts, a coat hanger with a tiny hook on the end
often works to remove the expanding nut if your patient.
On a weak wall I have extended the width of the top bracket & also put a 2nd
right angle on the inside (loft), with long studding joining the two together.
This is not ideal for the wall as U can crush the cavity wall, but it was 100x
stronger than just a 2 bolt T bracket!
U BOLTS
With many bracket, you get rough V shaped ³³ ³³
bolts that will dent the pole if it is a .---³³--- .---Þ³³--
thin one. This is unimportant if the bottom //~~~³³~~~ ú.ú~'\³³~~
clamp as that has to take the whole pole ((pole³³ ::pole ³³
weight, but it is to the top one, if the \\___³³___ úú._./³³__
pole is kinked at the clamp, as the pole '---³³--- '---Þ³³--
is highly likely to fold over in a storm at V clamp U clamp & Spacer
that point. It is better to replace it with
a properly shaped U camp & spacer, or at
least not over tighten the top clamp!
When lifting a pole through guiding U clamps
it is a useful tip to make use of the "ratchet" ³ ³ ³ ³
effect. This is where a loose clamp pressed ³ ³ Press ³ ³ Hold
down at the centre of the U will grip the pole, =Þ~Ä-.v =Þ===< level
but pushed up/kept horizontal, will let the ³ ³ Down ³ ³
pole rise. Again be aware of putting excessive Locked Free to
down force on a T bracket, so always keep that pole lift pole
clamp very loose while lifting! Mind fingers!
Tape up/cable tie loose coax/leads etc. before
they go out of reach above the top clamp!
CHIMNEY LASHING
With lashing kits make sure you have
enough lashing wire to go around the
chimney. The corner protectors (p) can ³ ³
be difficult to place from a ladder, ³ ³
but putting them on the wire in ÚÄÄÄÄ¿ ³ ³
approximately the right place & poking C ³ ³ ³ ³Aerial
at them with a stick usually works. ³ ³ ³ ³Pole
Put the wire onto the bricks not into H ÚÄÄÄÁÄÄÄÄÁÄÄÄ¿ ³ ³
the weaker cement course where it ÀÂÄÄÄÄÄÄÄÄÄÄÂÙ ³ ³
could cut in & loosen. I ³ p __³__³_³_
Ã)----==³]= o o³Top
As to spacing, the same fixing M ³ J ~~³~~³~³~ lashing
decisions as for a wall apply, except ³ ³ ³ ³
lashings actually help support the N ³ ³ ³ ³
masonry if there is any cracking etc, ³ ³ ³ ³
& there is less point loading. But the E ³ ³ ³ ³
lashing must be tight & wire fastings ³ p __³__³_³_
to the adjustment J bolts must be good. Y Ã)----==³]= o o³Bottom
A twang of the wire is a good ³ J ~~³~~³~³~ Lashing
indication there is a 50kg load or ³ ³ ÀÄÙ
so on it. Painting the lashing wire ³ ³
anywhere the zinc plating that was ³ ³
worked on with tools around the Js & (p)
does reduce rusting.
PAINTING
Not done commercially, but a well painted bracket/lashing will reduce the rust
marks & increase lifetime.
If you intend to remove clamps in the future then greasing the threads before
doing up the bolts is wise, but also paint the exposed clamp to seal in the
grease, this keep nuts from turning & also stop excessive thread rusting.
EARTHING
If your worried about lightening, then add an earth wire straight to a ground
stake from the bottom bracket. The gauge of wire does not matter really, as any
thickness will static earth it OK (once!) & even 5A fuse wire will take 10,000
amps as it arcs on the 1st pulse! Earthing will take away nearby pulse currents
of a few amps which may save preamps etc, but for much more protection than
that it is normally a waste of time & money, as you have to go a very long way
to protect your shack from a direct hit!
THIRD SUPPORT
With a heavy top load, using a 3rd (another T) one between well spaced top &
bottom fixings will stop the pole bending too & throw & reduce some of the
swaying at that resonance. This improves the look & also spreads the load more
evenly, giving some improved margin of safety, but getting it in true vertical
line not always easy!
GUYING
It is not normal to guy such a pole, but if
large wind loading or heavy rotator & stub ³ ³
pole are to be put up, there can be an ³ H O U S E ³
annoying to for the whole lot to sway the ³chimney[_] ³
breeze. This can easily be stopped with ³ : ³
light guys (strings). Suitable guying ³ : ³
positions need to be found (e.g. right angle ÀÄÂÄÄÄÄÄÄÂÄÄÄÄÄÄÂÙ
shelf brackets to clear gutter overhang) ~ Ä ú o ú Ä ~house
as well UV stable rope or thin single : guys
stranded steel fence wire (plastic covered) rear:
works well, but need eyelets to stop guy or:
braking. aerial:
If your into HF consider adding insulators :
& making these into dipoles, but they may
be too near house QRM to be very useful!
If off pole guying is not practical Aerials & Rotator
but you still want to stop swaying ³³
& improve rigidity, consider what /³³\
ships do with a cross brace & guy / ³³ \
back to & bottom of the pole. \ /__³³__\
The brace is a cross attached to the \ \ ³³ /
pole in the middle, The 4 arms then _____\_\_³³ /
have steel guy wires over them from HOUSE³~\³³/_turn buckles
near the top to near the bottom & ÃÄÄ´³
each one has a adjusting tensioner. ³
STRING FUSES
With guys or wire aerials that could pull down the pole, if say a tree fell
on them, then use a weak string/cordage as a mechanical safety fuse, so that
the aerial comes down first & not the pole!
NOISES
There can be several source of this. Windage across open poles, this can be
stopped by plugging/capping them (bottom ones need small holes in to let water
out).
Creaking noises when the wind blows need investigating, as they are often an
early warning of something wrong. e.g. loose wall bolt/screw.
Rotator wering noise, can be reduced by servicing the rotator, & using plenty
of really thick grease, & also under running the motor (see buls on rotators).
Rattles/clanking can be due to movement, even very small can sound loud in the
middle of the night. Use packing e.g. carpet/lino to reduce/fill gaps on moving
parts to stop noise.
Halyard slapping occurs when a rope is under tension parallel to a pole with
wind passing (e.g. flagpoles). The cure is either dampen the resonance out with
say a sponge wedged in, or move the rope further away to that is can't hit the
pole.
SAFETY
Remember if working above 2M always have someone else to hand who can advise or
even call for assistance. A fall from 2M to concrete with your head can kill.
Ladders free standing need a 1 in 4 angle (75deg), & secured if at all
possible. Someone footing the ladder by standing on the 1st rung is
recommended.
Hardhats for any one the could have things accidentally fall on them or even
bump into overhanging eves etc,
Power tools are dangerous & difficult to use on ladders so take extra care. A
small shock from one at ground level is a tease, but up a ladder can be fatal,
so always use a safety trip cut (ELCB) as well as well maintained leads.
Eyeshields are need when drilling, as blown brick dust can easily get in your
eyes. Also useful when manhandling VHF/UHF beams with the small elements which
can easily poke your eye out when you least expect it!
Safety footwear can protect from crushing toes, but also can be more relaxing
on ladders with a good solid sole & heal.
Leather Gloves, these protect hands from sharp object & may help you grip
ladders & poles better, but are a real nuisance when handling nuts & washers!
Open finger gloves/mits can be quite effective, by keeping hands warm & fingers
still feeling on a cold day.
Safety mainly comes down to "Good decision making", so think 1st.
See my other buls on "Gyn polling up large masts", "Tree Antenna Sky Hooks",
"A Light 17m /P mast design" & "PL259 Losses".
Why don't U send an interesting bul?
73 De John, G8MNY @ GB7CIP
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