One design for making parabolic radio astronomy dishes is to use a geodesic design – how do amateurs make a parabolic dish using this?

Amateurs use geodesic techniques to approximate a true paraboloid with many small, flat facets arranged on a spherical/geodesic framework, then “pulled” into a parabolic shape. The approach is popular because it avoids heavy machining while still giving good RF accuracy.

Here are the main amateur methods, from most common to more refined.

1. Geodesic frame + parabolic “set” (most common)

Concept

• Build a geodesic dome–style frame (usually aluminum tube or wood struts).
• The frame itself is not parabolic—it’s close to spherical.
• The reflector surface is then adjusted so all points lie on a paraboloid, not the struts.

How it’s done

1. Design a geodesic sphere section
   • Use a standard 3V, 4V, or 5V geodesic subdivision.
   • Software like Stellarium Dish, K3PGP Dish Designer, or spreadsheets convert this into strut lengths.
2. Choose focal length
   • Typically f/D = 0.35–0.45 for radio astronomy.
   • Paraboloid equation:

     z = \frac{r^2}{4f}

3. Set parabolic depth
   • Use a central mast at the focus.
   • Run strings or rods from the focus to each vertex.
   • Adjust each reflector panel so its surface touches the correct string length.
4. Attach reflective surface
   • Galvanized wire mesh
   • Expanded aluminum mesh
   • Perforated aluminum sheet

📡 Accuracy is determined by panel size, not strut accuracy.

2. Faceted “true” geodesic paraboloid (more advanced)

Instead of correcting a spherical dome, amateurs sometimes design a paraboloid directly subdivided into triangles.

Method

• Start with a paraboloid surface.
• Subdivide into triangular facets numerically.
• Each triangle is flat, but tangent to the paraboloid at its center.
• Panel corner offsets are small and acceptable at radio wavelengths.

This requires:

• CAD software or Python scripts
• CNC or careful jigs for panel shaping

Used by:

• Advanced amateurs
• University projects
• 1.4 GHz (21 cm) work and lower

3. “String method” for final shaping (classic amateur trick)

This is often combined with Method 1.

Procedure

• Place a pole at the focus.
• Attach equal-length strings from the focus to:
  • the rim
  • intermediate vertices
• Each string length equals the distance from the focus to that point on the paraboloid.
• Adjust mesh tension until it just touches each string.

This gives surprisingly good accuracy (±2–3 mm on 3–5 m dishes).

4. Wire-mesh geodesic dishes (cheap & effective)

Very popular in amateur radio astronomy.

Build style

• Geodesic strut skeleton
• Fine mesh clipped or tied to the frame
• Mesh tensioned parabolically using:
  • central hub
  • radial wires
  • turnbuckles

Mesh spacing rule of thumb:

\text{mesh spacing} < \frac{\lambda}{10}

For 21 cm:

• ≤ 20 mm mesh is fine

5. Why geodesic works well for radio

• Radio wavelengths tolerate small surface errors
• Geodesic frames are:
  • Strong
  • Lightweight
  • Wind-resistant
• Easy to scale to 3–10 m without heavy tooling

For 1420 MHz:

• RMS surface error ≤ λ/16 ≈ 13 mm
• Many amateur geodesic dishes achieve 5–8 mm RMS

6. Typical amateur examples

7. Software & tools amateurs actually use

• Dish Designer (K3PGP)
• Geodesic Dome calculators
• FreeCAD / OpenSCAD
• Spreadsheet paraboloid solvers
• Fishing line + turnbuckles 😄

Practical advice (from experience)

• Don’t chase optical perfection—panel size matters more
• Build the frame stiff, adjust the surface later
• Choose f/D early—feed design depends on it
• Mesh tensioning is easier than rigid panels
• Measure with strings, not rulers