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G8MNY > TECH 21.07.16 14:23l 291 Lines 14513 Bytes #999 (0) @ WW
BID : 11750_GB7CIP
Read: GUEST
Subj: Gin polling up large masts
Path: IZ3LSV<ED1ZAC<GB7CIP
Sent: 160721/0917Z @:GB7CIP.#32.GBR.EURO #:11750 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Updated Jan 16)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
A 20M MAST
Over the years I have tried several aerial systems. But settled on a well tried
& tested gin pole system.
The biggest used to date uses 3x 21' (3x 6.5m) aluminium scaffold poles with
reinforced Jaybeam joiners & a 42'(2x 6.5m) steel gin pole. (as we are getting
older a 2nd gin pole is used for putting up the gin!)
.ú:Ý,Pulley
3 tiers of 4 guys @ 90ø ,ú'.;'Ý \
ensures stability. Tight,ú' .', Ý `\
3 Guy ,ú' ,' ,' Ý `\
This design is the Sets,ú' ,' ,' ÝGin `\
mainstay of nearly ,ú' ,' ,' ÝPole `\ Gin
all my contest & ßßßßßßßßßßßßßßßßßßßßßßÝ ` Pull up
/P activity. 20m Mast Ground^ Pivot Rope
Structures higher than 66' (20m) have been attempted, but computer calculations
showed this to would be unstable, & these were borne out in practice when
unstable attempt proved it, i.e. they tend to buckle the mast on lifting with
any head load at all!
METHORD
The mast is always put up with NO aerials first, to make sure all the mast bits
work properly & are in the right place before, the mast is loaded up. With the
aerial load the mast should be raised slowly & a spotter person used to sort
any snags out. Generally you can tie off the gin up rope at any angle up to the
point of balance, above that someone should slowly pay out the rear 3 mast guys
to stop any sudden shock on the mast as it comes vertical & the rear gys
tighten.
If there is to be any length of unsupported mast above the too guy ring, like
in a 17el over 17el on 2m, then an extra top guy is needed during gining up the
mast to stop the top of the mast bending away from the gin (when total collapse
failure is possible!). And this is then untied from the gin & allowed to rap
around the mast when in use.
REINFORCED JOINTS
________________
³o o o o o o³
-----------³~~~~~~~~~~~~~~~~³---------
Mast Poles ³ÍÍÍÍÍÍÍØØÍÍÍÍÍÍͳWebbing
-----------³________________³--------- [³³]
³o o o o o o³ / \
~~~~~~~~~~~~~~~~ WebbingÄ´ ÃÄ
_.-Ä~~~~~~~~Ä-._Webbing \ /
-----------³~~~~~~~~~~~~~~~~³--------- [³³]
³================³
-----------³________________³---------
~Ä-.________.-Ä~
To stop the joiners tearing along the perforated centre line, extra steel
webbings (0.4 x 2 x 25cm) were welded over the weakness both sides. To lighten
it a bit the webbing ends can be cut down.
SLIPPING JOINTS
If the joints stretch & start to slip [³³]
(aerial poles rotate), then put a / \
thin wire (coat hanger) under one of Ä´ .ÃÄ
the sides & clamp up, this will bite \ /\Wire
into the smooth pole & stop slips. [³³]
GUY BEARINGS
Made from either plate or tube collars, resting on a large 2" (50mm) greased
ally washer above the joiners. The top set of guys will rest on an exhaust U
clamp, it also has an enlarged guy spacer is needed to stop the steeper guys
rapping around the pole.
³ ³ Plate ³ ³ Tube ³ ³ Top
==³ ³== Or ,o´³ ³Ão, oÄÄ´³ ³ÃÄÄo
.' ÚÁÄÁ¿ `. .' ³³ ³³ '. .' ³³ ³³ '.
.' ³| |³ '. .' /~ÚÁÄÁ¿~ '. .' /~µ Æ~ '.
³ ³ Washer³| |³ Washer ³ ³\
Exhaust U Clamp
Never use a long unguyed pole (e.g. 10ft) above a guyed joiner, as the wind
loading on your aerial & the pole leverage will try to sheer the joiner in two!
Always use a top guy set & U clamp close to the aerial as possible.
Halyard pullies for wire aerials etc. can be put on the top guy set to, so they
do not rotate with the mast.
CENTRE GROUND POST
(plan views)
Gin ³ ³ Ground Ground Ground
Pole³ ³ Post Post Post
³ ³ (_)___Swivel Mast (_) (_) Swivel clamp
ÄÄÄÄÄÄÄÄ´ÄÃÄÄÅÄÅÄ¿ Clamp ÄÄÄÄÄÄÂÄÂÄÄÅÄÅÄ¿ Mast-( )
ÄÄÄÄÄÄÄÄ´_ÃÄÄÁ=ÁÄÙ ÄÄÄÄÄÄÅÄÅÄÄÁ=ÁÄÙ ÚÅÄÅÄÄÄÄÄÄÄÄÄ
Mast 90øClamp (_)\Tight ÀÁÄÁÄÄÄÄÄÄÄÄÄ
lose Gin pole Clamp 90øclamp Gin Pole
All on the ground Gin up in air Mast up
The gin pole clamp is left slightly lose on the mast so that when the gin is
errected from the side it can rotate on the mast.
GROUND LAYOUT o
All guy ropes use | (5x 5x 80cm)
a safe "clove hitch" | stakes
knot on the bottom of |
the angled stakes. Front Ground | Gin
Stake Post |--goes down---> Back
Once the mast is =======o==========`8<-----12m----->o Stake
up & no further Mast' | -~
adjustment is needed | _-~
the clove hitch can Hinge| 17m
be locked with a. Line| -~
simple over knot. | _-~
o~ Side stakes
A short 1m x 49mm steel ground pole is put it the middle (after making a hole
with the spare 5th stake first) to take all the hinge forces.
ROPES
A full mast rope set of 3 tiers of 4 guys & a gin pole pulley system + 2 guys,
takes 1,024' (312m) of rope. Using mainly 8mm polypropylene for strength &
cheapness, caused a storage problem, as the rope is ultra-violet light
sensitive. For speed we do not detach the measured ropes from the guy bearings
for neat rope hank storage, so a single guy tier of 4 ropes with its bearing is
chain-laced together to give quick & untangled storage. The bulky & UV free
storage was solved using 2 large dustbins (for 3 mast sets). One for the 1st
mast & Gin pole, & the 2nd for the rest of the masts.
GIN PULL ROPE
ÚÄ¿Thick
³~~³³hook This is a thicker 20mm
_ððððð Ropes for hand hauling & uses
Mast _-~_ððððð (clove hitches) a 2:1 pulley on the gin
top_-~ _-/³ | ³o\ pole that hooks on the
_- / ³ | ³\/\Strong pole with the mast ropes
middle / G³ | ³ \ \Pulley tied over the hook.
/ i³ | ³ \/\
/ n³ | ³ \\\Gin Ropes
bottom Side \\\
Guy \\\
The gin pole will need 2 side guys, these need not be @ full length 2/3 is OK.
GUYS
The top guy to the gin needs to be low stretch & pre-tightened so that the top
of the mast ALWAYS bends (curved up) towards the gin pole. This avoids the
unstable failure mode when the top guy ends up in parallel to the mast & the
very high compression forces on the mast cause a collapse.
.ú:Ý, .ú:Ý,
,ú'.;'Ý \ ,ú'.;'Ý \
,ú' .', Ý `\ ,ú' .', Ý `\
3 Guy ,ú' ,' ,' Ý `\ 3 Guy ,ú' ,' ,' Ý `\
Sets,ú' ,' ,' ÝGin `\ Sets,ú' ,' ,' ÝGin `\
.._,ú' ,' ,' ÝPole `\ ,ú'__...:_ ,' ÝPole `\
~~~ÄÄÄ---...:.____Ý `\ _.:-~~ ~~Ä-..__Ý `\
Good Curved Mast ^ Pivot -~Unstable Mast Fail! ^ Pivot
COAX TIES Beam Boom
With a rotary mast system reusable ù===ù=ù===ù=Ë=ù===ù===ù===ù
coaxes ties were used on the coax & ~==___º__-Ä~Support
reused to attached it to the mast Coax/ ~~º> coax
above the top bearing. Then 1 or 2 <º loops
lose turns/loops & then attatched Tie.'º'.U clamp
to one of the top bearing guys with .' |º '.bearing
a cable tie threaded through the rope. .' |º '.
(stops it slipping down the rope) .' Coax|º '.
This is then repeated at each lower .' Tie.'²'.joiner'bearing
bearing to take each section of the .' .' |º '. '.
coax's weight, & also keep the coax .' .' |º '. '.
away from the bearings. .' .' |º '. '.
.' .' |º '. '.
TRANSPORT
With the large poles, only roof racks could be used, this caused noticeably top
heavy problems with the vehicles. After some research we solved the problem,
with a designed for a dismantleable pole trailer. The UK law on the length of
long trailers is simple, the trailer other than it's drawbar, must not be
longer than the divisible load.
______
Welded Ý(__[]__)Þ Arm & rubber [³]
Tow .ú'Þ] Wheel frameÝÄÄÄÄÄÄÄÄÞ suspension ³
Hitch úX====X==========================X========X==================X=³
.ú' Þ Þ Ý Þ Þ ³Tail
0<'| Þ Þ Centre pole()XBrace Þ X ³Board
'ú. Þ Þ Ý Þ Þ ³
Welded`úX====X==========================X========X==================X=³
Draw A 'ú.Þ] 2x steel poles (gin) ÝÄÄÄÄÄÄÄÄÞ ³
Frame Ý(__[]__)Þ [³]
Wheel unit
X = scaffold clamps. & mud guard
ù poles
[ forward lights _.-XÄ-.._
] rear light _..-''~ Þ ~`Ä.._
_,.-''~4m 1m Þ [] 3m``Ä-.._
_..-''~ Pole PoleÞ /~~~~\ Pole ~``Ä-.._ o [³]
_ =X====X=========================ÞX³ /~~\ ³X=================X===
(_\____ù____ù_ Þù³³ {} ³³ù
~~~~~~~~~~~~~ \__/Mini
Wheels
We welded up the design, & it has lived up to all expectations, regarding
cornering & loadings etc. The only problem has been the requirement to manually
drag the rear & around tight corners like at the contest site entrance. With
experience the wheel unit can be clamped at a position to set the hitch load to
50kg, dependent on the planned trailer load. As well as the tail board there
are 6 additional running lights to make the trailer conspicuous as well as
being painted in bright colours. The wiring loom is rapped around the poles &
plugs in the fixed lights etc.
There are 2 shorter bracing poles, that form 2 triangles & are tensioned up
before moving by standing on the long steels & doing up the top swivel camps,
this then forms a very ridged trailer.
The trailer can handle 6 Ally scaffold poles clamped on plus loads more on top.
So it can carry poles for 3 masts using the 2 steels as the shared gin.
The pole trailer is completely dismantled for storage.
AERIALS USED
Mainly concentrating on VHF contests, I have used quite a collection...
BAND
160m 100m random wire to halyard to trees, many other dipoles too!
80m Insulated 66' mast as 1/4 Wave vertical
80m/40m Trap Dipoles, inverted Vs & also plain QRO dipoles
20/15/10m 3el TH33 Mosley beam with QRO traps
6m 3el Coax & Bamboo Quad
6m 5el yagi beam
4m 2x 5el yagi & phasing harness
2m 5el, 7el, 11el small beams, 17el & even 2x 17el 11ft apart
2m 4x 17el yagis Box, 11ft apart stacking frame & power splitter
70cm 9el, 19el, 23el yagis, 88el multibeam
70cm 27el quad loop yagi
23cm 24el, & 65el loop yagi
13cm 40el with tranverter on 10ft extention pole
For 2m we used to use a box of 4x 17el, stack/baying frame & 4 way power
splitter, but due to its weight it could only be put up at 42' & took a good
hour to assemble onto the mast. This gave a theoretical 20dB gain or 40kW ERP!
However the simpler, 2x17el staked at 10'(3m) apart with a coax splitter works
as well in practice at 20m with is wider beam width.
On 4m we stacked 2x5el at 10'(3m) apart as well.
ROTATORS
Generally I use mast ground rotation, avoiding putting the heavy rotators at
the top of the mast. The slightly faster arm strong methods, have been
superseded with bottom of pole rotators, mainly because of access to the mast
under all contest weathers. But I have seen direct drive gearboxes & shaft into
the shack used on simular masts.
_³_³_____________________________
To put a heavy mast on |__________________________ Gin Pole
the rotator, either have ³ ³ ³³
several helpers to lift a /³\ ÝÞ
tiller bar with the guys ³ ³ ³ Þ__Ý Jack
fairly loose. Or use a car ÚÄÁÄÁÄÁÄ¿ ³ ³
jack under the horizontal ³ROTATOR³ ³ ÃÄ¿
gin pole to lift the load Bracing __ÀÄÄÄÄÄÄÄÙ_ ÁÄÄÁÄÙ
while you assemble the Feet U U
rotators clamp on the pole. OR Bolts in
ground
EARTHING ÚÄ¿____³ ³
A when the whole mast is rotated ³X³~~~~³ ³)
I put a flexable 1-2 turn earth ³ ³ ³./
strap from the ground post to the ³ ³ /³\
mast rotator clamp. ³ ³ ³ ³ ³
This earth will take some of the ³ ³ ÚÄÁÄÁÄÁÄ¿
nearby lightening current safely ³ ³ ³ROTATOR³
to earth & not via the shack. ³ ³ ÀÄÄÄÄÄÄÄÙ
N.B. Any direct strike will do ³ ³ U U
lots of damage! ³ ³
WINDAGE
Generally this is not a problem as the gining up process puts much higher loads
on everything than the wind will. Do check guy tensions & knots at least once a
day & after/during any storms. If there are problems & you have the extra rope
it is possible to add an additional guy in situ by lassoing a mast guy set at
ground level & slipping the new guy up the others & stake out windward etc.
In strong wind raising & lowering, should ONLY be done side on to the wind! So
the only effect it has is to keep one side set of guys tight, & not help/hinder
the mast raising & lowering.
Y Don't U send an interesting bul?
73 de John G8MNY @ GB7CIP
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