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