GROUND POLE: The major item
here in setting the ground pole is plumb, plumb, plumb - make
sure the pole is perfectly vertical; though first thing, check
for obstacles in your viewing path
and choose appropriate pole for your dish diameter (see wind
loading). Rule of thumb on minimum hole diameter - four times
diameter of pipe. Rule of thumb on hole depth - minimum one/third
down  (below ground) and two/thirds up (above ground). Rule
of thumb on gravel size for concrete - no bigger than one/half
distance of pipe to side of hole. Rule of thumb on concrete type
- never use 'quick crete', i.e. concrete with additives for one
hour curing, it will crack in years to come and sometimes as
little as in six months . If you are not using a premix of concrete
then use the one-two-three rule: one part cement, two parts sand,
three parts pea gravel. When cutting pole to length be sure ends
are square - it will cause you plenty of problems if they are
not. Remember that concrete shrinks when it cures (concrete does
not 'dry', it cures) and actually pulls away from surfaces as
it hardens so weld a flange, or spur, to the bottom of the pole
for to anchor pole into concrete as it hardens. A flange on one
side is sufficient, both sides is overkill. Sometimes I have
just drilled a hole thru the pipe and stuck a rod thru the holes
with no welding. When digging hole - get below frost line and
flare out the bottom of the hole so concrete will make a good
plug when poured (make the hole look like an elephant's foot).
Place a thick layer of gravel on the bottom of the hole, or
at least a brick but gravel 'seats' the pole better, and set
pole in hole on gravel. Do not try to pour the whole concrete batch at once. Make the first
batch stiff (thick), position pole in center of hole, and shovel
small amounts of concrete equally around the pole. If you shovel
too much concrete to one side at once, especially in the beginning
of the pour, it will push the pole to one side and you will lose
center; be patient and take your time here. Pour enough in first
batch to bring concrete about a foot up on the pole. Now take
a rod, something like a piece of rebar, but a shovel handle is
too thick, and gently 'rod' the concrete, i.e. push rod straight
down thru concrete to bottom of hole - be careful not to do so
in a manner that causes the pole to lose center. Do this no more
than ten to fifteen times, this ensures no air is trapped in
mix; if you rod more than that then the mix begins to come apart.
Check pole for plumbness all around, not just on one side, with
level or inclinometer - hold pole for a few minutes now (good
thing for assistant or mother-in-law to do). Do not be lured
into thinking that pole is plumb because top is level - that
depends on the saw cut; make the sides plumb. Make next concrete
batches with more water and gently shovel into hole in small
amounts being careful not to pour too much at a time or you will
disturb pole plumbness. The reason the second batch of concrete
is made with more water is because soupy concrete cures to have
more strength. Repeat rod procedure, extending only slightly
to level of first pour, and check for plumbness.
 At this time set a PVC elbow in concrete that extends
out beyond the hole wall and is against the pole and extends
up the pole high enough to be above lawn mower or weed eater
height. You can cap top of PVC later with downpiece - what is
important now is to seal both ends of elbow with good tape to
keep debris and concrete out of pipe. I have set elbow in concrete
and set it above last pour - your choice - I usually set it in
pour at depth below grass root level. Finish pour to top and
rod last batch; sculpt the top so that concrete slopes away from
pole. If you want, bring concrete to above ground level or leave
below ground level so as to add a grass plug later. At this time,
pole should be difficult to move because of thick concrete in
first pour though later soupy pours will take some time to cure.
Recheck for plumbness and push pole to any direction required
to be plumb - it should not be far off, if at all, if you have
been checking regularly - hold.for a few minutes while you drink
a cup of coffee, tea, cola or have a smoke. In about an hour
fill the pole with very soupy concrete to at least above ground
level - this will add strength to the pole as well as prevent
future oxidation (coming from internal of the pole) of the pole
at the ground/air interface.
For four meter or larger residential antenna, use a larger
diameter pipe than recommended and place a reducer cap on top
when ready to install reflector, i.e. if the mount cap comes
ready for a 3.5" pipe then use a 4.0" or greater main
pipe diameter and weld a reducer cap on top with a 3.5"
diameter that the mount cap will slide on. For more info on pole
diameter, see wind loading. Remember:
When choosing the site for the ground pole be sure that when
the dish is rotated from arc to arc it will not touch anything
and that it will have a clear view of the satellite arc from
end to end.(top of page)
PAD POLE: Where hard rock
prohibits a ground pole, or for installations in a parking lot
or on a flat roof, it becomes necessary to anchor the satellite
dish with a little more creativity. The most easiest is to weld
a crosstie leg assembly with a welded support brace going from
each leg up to the pole; then weight down each leg to immobilize
the dish. I am currently in a rent house, flat roof, so do not
want to permanently install my dish in a concrete pad on the
roof so I use unopened eighty pound cement bags (not quickcrete
with gravel and sand but pure cement) on each base leg as a weight.
With rain, over time, it will harden like a rock and mold itself
to the base leg. For a rule of thumb, for an installation on
a flat roof atop an office building, for a 3m dish, use a total
leg base of eight to ten feet (four to five feet per side) and
use something like four inch channel for the leg and one or two
inch angle iron for the braces (do not use flat bar for braces
but you can use round bar). In practice, position the pole and
base on roof then level the base with shims so that the pole
is plumb then apply leg weights (use a pile of rocks if nothing
else). For my system, an eight foot dish on a one floor roof,
I have two foot length legs out of one inch angle iron with sixty
degree round bar braces from each leg to the side of the pole
- all welded. I have come out one-half the leg distance and up
at a  sixty
degree angle to the pole. Note: Often after a weld, the legs
will 'pull' a bit. In my case, that occured however on the roof
I leveled each leg with shims so the pole was plumb then piled
the weights on the legs and and a few rocks around the pole.
Remember to check the pole for plumbness after piling on the
weights.
In lieu of the 'crude' system described above, you can use
a combination of a mount pole outfitted with legs set onto preformed
concrete end weights. Preform the leg weights, mass production
style, as concrete blocks, use ready mix sacks, i.e. not large
aggregate (gravel) and inset a 'J' bolt for both leg attachment
and  pole leveling. Concrete is stronger the soupier it
is so do not wipe water off the top and if need be, on real hot
days, place a burlap sack on top and wet it down after your last
pour. On real cold days, add a combination of straw, newspapers
and rags on top to prevent freezeing. In designing your forms
use an assembly that you can bolt to a bottom plate (1"
plywood). Make the side boards at least from 2" x 6"s
to allow sufficient depth for the 'J' bolt. Depending on the
size of dish to anchor you can make the blocks with 2" x
8"s, 2"x 10"s or 2" x 12"s. On the bottom
of the form nail (or screw) a 'lip' all the way around (use a
1" x 6") and use this lip to bolt to the bottom plate.
The lip and bolt down prevents concrete from oozing out the bottom
of the form, use mimimum two bolt downs per side. When cured,
remove the bottom plate and hopefully you can dump out the mold
and reuse the form - concrete actually shrinks when it cures
so you are making a reuseable form.as the finished block will
pull slightly away from the form and will come out rather easily
but during the pour the form must be bolted down well to the
bottom plate. In lieu of 'J' bolts, you can take a threaded rod
and then thread nuts and washers to make the anchor in the block.
Make a jig for the top (from a 2" x 4") with a center
hole to place over the anchor bolt and thread a nut over the
exposed bolt to keep the bolt in place and vertical and to be
sure the bolt does not sink into concrete. Use the top jig, or
another board, to level the top before slipping in bolt, i.e.
wipe off excess concrete from pour. Use a mini-level (sometimes
called a torpedo level) to guarantee the bolt stays vertical.
Make the block in one pour and use medium stiff concrete at time
of pour but not too stiff that bolt will not slide in easily
- the bolt should slide in and concrete ooze around it easily
otherwise anchor will not be set to its best capability. Remember,
concrete actually shrinks as it cures so do not but in a straight
bolt without something to anchor it in the concrete or you will
compromise its stabilizing effect on the dish mount. Do not use
anything less than a 3/4" diameter bolt. If you are using
allthread for the bolts and/or have in mind to saw off the bolt
tops after concrete has cured, i.e. to level all the emplaced
bolts, thread a nut onto the bolt before sawing so that after
the cut you can work the nut off and reconstitute any threads
damaged by sawing.
The last real option to anchor a dish without a ground pole
is to pour a complete concrete pad.
The  major
aggragation to this is inseting the bolts to correctly align
with the dish pole support structure. The other option to inseting
bolts is, after concrete pad has completely cured, use
an epoxy system to anchor the required bolts. This technique
requires drilling the proper hole into the concrete then using
the epoxy system to secure bolt; a manufacturer's variation on
this is to epoxy (into the hole) the unit the bolt will thread
into then, of course, install bolt. These are proven, structurally
rated epoxy techniques and make a very nice installation; check
with any high quality hardware store to located the product (read
all instructions when using the epoxy system as there is little
for error once you begin the epoxy process). To properly mark
hole locations, place the mount on the finished pad then mark
with a chisel where to drill or, better, drill a starter hole
with a masonry drill bit before moving the mount to drill the
correct size hole.
The other option, for a full ground pad, instead of inserting
bolts, is to pour the pad (to level the install site) then use
a brace-leg-weight system to anchor the pole.
For the pad, set the pole with legs at the proposed location
and mark the size pad desired; then, remove pole out of the way
(of course), build your form. For a weight anchor system, minimum
pad thickness is using a 2" x 4" for the form edges
for a 2.0m or less diameter dish and go to a 2" x 6"
for a 3.0m dish and a 2" x 12" for anything greater.
Be sure to frequently stake the form perimeter as concrete is
heavy and will push out on the form. Nail form edges into each
other. Be sure top of form is level in both directions. If pad
site is unlevel and the bottom of the form is not touching the
ground in any place then fill inside of form with dirt to prevent
concrete leakage and pack the dirt firmly. Try to mix all concrete
you will need in the beginning then shovel into form. Resist
the temptation to throw in rocks/bricks, etc., to fill your pad
quicker. When form is halfway filled, lay in a layer of concrete
wire mesh then finish pour and level off top with a board, i.e.
scrap off excess concrete. Do not scrap off excess water on top
of pour; if anything, after an hour, spray more water on top
of curing pad. The extra water on top will assist in preventing
cracking. In laying the mesh on this small of a job, it is best
to do so in middle of pour rather than lay on ground and fill
concrete on top and try to 'shake' it up. The mesh is not so
much to add strength to the concrete but to hold it together
over time (maintain its structural integrity) should the pad
crack (due to whatever reason). In case of excess freeze-thaw
phenomena locations, i.e. in 'cold' country, using a weight-leg
pole assembly, rather than insetting attachment/leveling bolts
in the concrete, allows for easier leveling adjustment should
the pole become non plumb. When running cable, bury it, if possible,
to the pad then run through conduit atop pad to the pole; attach
conduit with strapping clamps to concrete using plastic screw
anchors inserted into drilled holes (use masonary bit) in the
concrete.(top of page)
WIND LOADING:The bottom line
on wind loading (on the surface of a dish) is the bigger diameter
the dish the more wind it traps and the more the dish faces into
the dish the more wind it traps. Mesh dishes act as solid dishes
at about fifty miles per hour though will still experience approximately
40% less force than a solid dish. To calculate the pressure on
the base of a pole, or where ever the pole is attached to a constraining
rigid structure (for instance, side wall of a house), multiply
the pole length by the factor in the chart, for the desired windspeed,
to get pounds per square foot  (psf); then divide by 144 to get pounds per square
inch (psi). This is a crude guide for you as other factors come
in play in determining actual shear forces on a mount pole from
wind - dish weight does factors in, i.e. the heavier the dish
the more force it will bear if the dish begins oscillating (which
contributes to fatique), and it changes the pole strength factors
if you have poured concrete into the pole. From the pressure
on the pole base and the manufacturer's characteristics of the
mount pole you can see if your chosen pole diameter is large
enough and its thickness sufficient to resist failure under maximum
winds. Believe me, nothing is more aggravating than dealing with
a bent mount pole after a windstorm. Use dish manufacturer's
guidelines in choosing a mount pole - do not leave it to chance,
especially on heavy large dishes. Remember, a good ground
pole installation, or pad mount,
and depth of pole, prevents a dish from eventually rocking or
leaning in the ground but does nothing to resist shear bending
above the ground. For dish diameter below 2.5m, with minimal
pole height, you can use schedule 80 (USA ASTM code) 3.5"
diameter pole. For dish diameter 3.0m using and regular height
poles (mesh, fiberglass or solid dish) and taller poles for diameter
2.5m, use schedule 40 3.5" diameter pole. For taller poles
above ten feet, in the previous two examples, use some type of
side wall support or turnbuckle/wire rope bracing system or expect
wind action on the Ku satellites. For 4.0m dishes and commerical
installations (not az/el type mount), use schedule 80 pole and
go to 4.0 and greater pole diameter - ask dish manufacturer.
For these larger diameter dishes they often refer to the 'pole'
as a pedestal and usually the manufacturer will recommend and
provide the pedestal or a tower for dish support.
Under no conditions, use PVC (plastic pipe) for any dish mount
(I have never heard of it being successful), and never underestimate
the power of inclement weather to damage your dish. For commercial
installations, I have installed retainer clips around dish lip
attached to wire rope (3/8" wire rope minimum) attached
to 'J' bolts in concrete posts so if the mount failed (not the
pole) then the dish would not fly around. Although we think of
failure of the pole, the shear strength of the bolts in the mount
are to be equally considered in your design criteria in wind
loading. In summary, if you have continued worries about pole
failure, have an engineer calculate wind loading forces on reflector
and the force moment at the ground/air interface (bottom of pole)
and choose pole diameter accordingly. I also use three support
cables (3/8" wire rope minimum) placed two/thirds of the
way up the pole for stabilization when needed to stay on track
in wind or for a free standing tall pole, and tighten with a
turnbuckle. Weld 'eyes/ears' on pole for wire rope and anchor
at a thirty degree angle from pole to 'J' bolts seated in concrete
pods. Your local hardware store will have everything you need.
(top of page) |
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