9.2 METER (30 Ft.) DIAMETER DISH PROJECT
FOR EME AND RADIO ASTRONOMY
Figure #1 Figure #2
Figure #1.This is a transportable earth station antenna I obtained from surplus. It normally would deploy on a trailer as shown. The trailer must be securely fastened to the earth before any assembly can begin. This shows the antenna as it is about to be raised for the first time. Picture was taken back in the mid 1980's. This transportable earth station was originally built by Comtech. Figure #2. Another shot of the antenna after assembly prior to raising.
Figure #3. This the steel beam and angle iron construction which fastens to and supports the aluminum trusses. The dish consists of 24 aluminum panels. Trusses and panels alone weigh 2400 pounds.
PERMANENT INSTALLATION:I plan to significantly modify this antenna structure for permanent mounting. This sketch in Figure 4, shows the current portable design. The dish mounting structure is actually part of the trailer. I have cut off the back of the trailer that includes this structure and will eventually mount it on top of a tower. The elevation mechanism uses a 20 ton actuator (jack screw).
The sketch in Figure 5 shows the octagon structure of the 8 primary trusses and the connection points from the aluminum to the steel. There are three intermediate trusses between each primary (not shown).
Figure 6 shows the planned configuration (To be revised for piling foundation). I plan to mount the rear of the trailer on a 30" thrust bearing as shown on the sketch for mounting on the tower. I have shortened the three main steel support beams by 52" to improve the mechanical advantage for the elevation system. The jack screw which came with the unit is a 20 ton unit with a hand crank which requires 1230 cranks to go from 0 to 90 degrees. Azimuth and elevation will be motorized and computer controlled. Target rotation speeds are 0-90 in 2 minutes and 0-360 in 5 minutes.
The tower is a triangular 6 foot face with 8.625" diameter legs of 0.322" wall thickness, rising to 12 ft. above ground, driven to 18 ft. below ground. I plan to design for maximum windload in the zenith position, since I will not operate during any appreciable winds. The following sketch is the antenna in the zenith position.
Tower Construction Details (Old version prior to the tubular steel design - see STATUS):
Dish AZ/EL Mount Construction Details (This one is current):
Windload and tower design details (To be revised for pilings):
WINDLOADING AND FOUNDATION CALCULATIONS
The following assumptions were used in the calculations:
1. Design windspeed = 50 lbs/sq.ft. (approx. 120 mph)
2. Two legs of the tower face away from maximum wind direction.
to reduce potential for buckling of the tower.
3. Design is with antenna parked (EL = 90; AZ = 150 +/-10)
(Historically all winds in excess of 30 mph are from this direction)
4. Concrete weight includes re-bar
Area of a parabolic section = 4/3 depth X radius
55" X 180" X 4/3 = 91.66 sq. ft.
Reduce by factor of 0.66 for cylindrical surface
91.66 X 0.66 = 60.5 sq. ft.
Windload = 60.5 X 50 = 3025 lbs
Moment = 23' X 3025 = 69575 ft-lbs
Weight = 1344 lbs
Perimeter Area of Truss = 82 sq. ft.
Reduce by factor of 0.50 for non-solid surfaces = 41 sq. ft.
Windload = 41 X 50 = 2050 lbs
Moment = 19.5' X 2050 = 39975 ft-lbs
Weight = 1056 lbs
Steel Mounting Structure Area
Aprox. 40 feet of 4" tubular steel = 13 sq. ft.
Windload = 13 X 50 = 650 lbs
Moment = 15' X 650 = 9750 ft-lbs
Weight = 2800 lbs
Tower (exposed) Area
3 X 12' vert. + 4 Horiz. + 12 diag = 31 sq ft
Windload = 31 X 50 = 1550 lbs
Moment = 6' X 1550 = 9300 ft-lbs
Total Tower Weight = 2452 lbs
(Including buried section)
Dirt [B]= 9' X 9' X 4' X 95 lb/ft +3933 [C] = 34,713 lbs
Concrete [A] = 9' X 9' X 2' X 150 lb/ft3 = 24,300 lbs
Total Overturning moment at tower base = 128,600 ft-lbs
Total Weight = 66,665 lbs
Counterbalance = 4.5 X 66,665 = 299,993 ft-lbs
Safety factor = 2.33
The dish AZ/EL mount will be fastened to a thrust (slew) bearing which was removed from a National 700 series 17 ton boom truck. It is manufactured by Kaydon and is 29.5 inches in diameter and weighs 263 pounds:
I have explored any zoning, covenants, codes or restrictions in my area, and I have consulted an attorney regarding any problems I might have with the erection of such a large structure. We have found nothing to prohibit the installation. I have reached an agreement on the location with the one neighbor who is affected. The figure below shows the plot plan.
I plan to frequently update the status of this project on the following page: STATUS
Stay tuned for future details on motor drives, gear ratios, braking systems, position indicators, power and RF cabling designs.
The aluminum sections and trusses were stacked as shown in the picture until July 2000.
Please send any comments to Mike
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