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Earth Moon Earth Communications
The challenge to build a very large Antenna
By Mike MelumPresented to ASPE June 13, 2013
Contents
• How I got hooked• The steps
– Design– Procure– The Tower– The Mechanics – Electrical/Electronic
MOTIVATION
• The Moon on a clear night is beautiful to behold• Typically about 0.5 degree of arc• Average 238,000 miles from Earth• The thought of reflecting a signal off the moon is
seemingly absurd, not quite as absurd as the thought of ‘going there’ but nevertheless not a normal quest
• Therein lies the challenge
How I got Hooked
• Ham Radio – since age 14• Amateur Satellites • The Ultimate ham radio challenge – EME
Hooked
• EME Attracts all kinds of people from carpenters to Nobel Prize winners (~2-3000 world-wide)
• Technology “Sport”– Civil, Mechanical, Electrical, Electronic– Astrophysics – Moon dynamics are complicated– Control systems– High Power Amplifiers– Low noise, high sensitivity receivers
The Steps
• Acquire the Dish• Design• Procure parts, materials, services• The mounting structure (Tower)• The Mechanics
Structural Design
• Tower Requirements – Strength– Height – Cheap
• Mechanical concepts• Make Drawings• Ask everyone!
Acquire a Dish
Original Dish
9.2 METER TRANSPORTABLE PARABOLIC DISH ANTENNA
50"
Modifications
DesignWINDLOADING 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. Total weight = 15 to 20,000 pounds4. Dish area = 700 sq. ft. 5. Overturning moment = 875,000 pounds ?6. Decision: Design for worst case in parked position7. Design is with antenna parked (EL = 90; AZ = 150 +/-10) (Historically most winds in excess of 30 mph are from this direction)
Alternatives
Tower (Pilings)
Tower TopTOWER TOP FABRICATION
AUGUST 31, 2000
18.0in.
VERSION 4
26 in. DIAM x 8 in. X 1/2 in. CYLINDER
(51.25 in.)
(56.5 in.)
18.0in.
28 in. DIAMETER x 3/4 in. DRILLED PLATE TO BE
MOUNTED ON TOP, WELDED TO CYLINDER (SHOWN HERE ON
BOTTOM TO CLARIFY POSITIONING OF CYLINDER
BETWEEN EDGE AND HOLES)
10.5in.
26 in. OD x 8 in. X 1/2 in. CYLINDER
(DIAGONALS NOT SHOWN)
4x8x1/4 in. TUBULAR STEEL
BOTTOM VIEW
65.5in.71.0in.
66.0in.
2EA. 6:1 SPROCKET SETS AND BAND BRAKE
Rotating Platform
75.0
in.
85.5
in.
8.0
in.
4.0i
n.
5.0
in.
36.1
in.
65.0
in.
29.7
in.
`
1.5in.
36.0in.
AUGUST 4, 2000
PLATES 10" X 28" X 1/2" STEEL
SCHED 40 3/4" PIPE SLEEVE REINFORCEMENT
SQ. X 1/2" STEEL
22 EA. 3/4" - 10 X 10 1/2" GRADE A325
4 EA. 3/4" - 10 X 2 1/2" GRADE 8
WELD
4 EA. 3/4" - 10 X 2" GRADE 8
REMOVE
MAX
BEARING
Rotating Platform (Part 2)
Elevation Actuator
Dish Assembly
Lift Frame
Crane
Mounting the FeedPhase 1
Mounting the Feed Phase 2 (First Attempt)
Mounting the Feed Phase 2 (Final Solution)
DISH SURFACE
TO WINCH
HINGE HINGE
TOP PIVOT
2.00
2.00 2.00
FEEDCONEMAY 22,2003
Mounting the Feed Phase 2 (First Attempt) (Continued)
DIY
Operating Console
Test Bench