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Satellite Dish Conversion

4 min read

A satellite TV dish is already a close-to-paraboloid bowl, so converting it means covering it with mirror tiles or reflective film, finding its focus, and mounting a target there. Compute the focal length from the diameter D and depth d with f = D² ÷ (16 d), watch for offset dishes whose focus is not on the visible centre, and mount it so it can be stowed: a 1.8 m dish in a 30 km/h wind feels about 160 N and in a 60 km/h wind about 640 N.

Part of Building Reflectors from Salvage

Satellite dish conversion repurposes a television dish as a solar concentrator by giving its surface a mirror finish and fitting a target at its focus.

Find The Focus By Measuring

A paraboloid of diameter D and depth d has focal length f = D² ÷ (16 d). Place a straightedge across the rim and measure the distance from it to the centre of the bowl.

Example: D = 1.8 m, d = 0.30 m: f = 3.24 ÷ (16 × 0.30) = 3.24 ÷ 4.8 = 0.675 m. Check it later with a card in the sun, as the parent page directs: hold the card at increasing distances and find where the bright spot shrinks to its smallest.

Many modern dishes are offset: the bowl is a slice of a larger paraboloid taken off its axis, so it looks nearly upright when it actually points up at an angle, and its focus sits off to one side of the centre. The formula applies to the parent paraboloid. For an offset dish the card test is the reliable method: aim the dish at the sun until its shadow is smallest and sweep the card in and out and sideways.

Wind: Why Dishes Need A Stow Position

Wind pressure is q = ½ × ρ × v². Inputs: air density ρ = 1.2 kg/m³; dish area A = π × 0.9² = 2.54 m²; drag coefficient assumed 1.5 for a bowl facing the wind (an assumption, not a measured value).

  1. 30 km/h = 8.33 m/s: q = 0.5 × 1.2 × 8.33² = 41.7 Pa; force = 41.7 × 2.54 × 1.5 = 159 N, about 160 N.
  2. 60 km/h = 16.7 m/s: q = 0.5 × 1.2 × 16.7² = 167 Pa; force = 167 × 2.54 × 1.5 = 636 N, about 640 N.

Doubling the wind speed multiplies the force by four. The parent page warns that a 2 m dish in a 30 km/h wind sees significant force; on a 1.8 m dish that is a push equal to the weight of about 16 kg at 30 km/h (159 ÷ 9.81) and about 65 kg at 60 km/h (636 ÷ 9.81). Tie the mount to the ground, use a stiff pivot, and point the dish face-down or edge-on in a gale (Wind Loads).

What You Need

  • A solid dish (the parent page: 60 cm to 3 m); mesh dishes pass the light through the holes
  • Mirror tiles or reflective film (Mirror Tile Parabola)
  • A sturdy arm for the target, replacing the thin feed-horn arm
  • A two-axis mount with locks
  • A cover

Method: Convert

Step 1: Clean the dish (parent page). Remove the receiver electronics and the thin arm, which will shade and melt.

Step 2: Measure D and d, compute f, and confirm it with the card test.

Step 3: Cover the surface: tiles glued with high-temperature adhesive, or stretched reflective film (the parent page suggests emergency blankets or balloon film). Film must be pulled flat; every wrinkle scatters.

Step 4: Fit a rigid arm to hold the target at f, adjustable in and out.

Step 5: Mount the dish on a base with azimuth and elevation pivots and a stow position.

Common Mistakes

  • Using the dish’s rim as the origin for the focus. The focus is measured from the vertex (centre).
  • Leaving the thin feed arm. It melts and drops its parts at the focus.
  • No stow plan. A dish loose in a gust becomes a sail and a projectile.

Safety

A converted dish ignites wood and blinds from a distance

A tiled dish of this size gives about a kilowatt at its focus, which ignites wood at once and burns skin. Never look at the focus or the reflection in the tiles, wear eye protection when adjusting, and cover the dish whenever you leave it, because an un-tracked dish still sweeps its focus across whatever is in front of it as the sun moves. Do not stand in front of the dish between the mirror and its focus.

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