Uploaded February 2025 | Updated September 2026, 2 weeks ago
As a kid I had a "rocket radio", a small, portable crystal radio with a 1950s space theme. I've been working at recreating that. This is a capacitor tuned version. It should be able to receive 4-5 stations which is 3-4 more than the typical rocket radio. It requires both a ground and an antenna (the rocket radio just had an antenna connection.)
3D Printer Files: thingiverse.com/thing:6934296
It uses a capacitively tuned coil in the ring of a classic space station with radar tuning. We explore the challenges of coil design, impedance matching, and tuning efficiency. While the prototype currently picks up two stations, my goal is to push performance toward three, four, or even five stations through coil optimization, wire gauge experiments, and improved Q factor. We'll look at the design diagrams, adjustments, and experiments I’ve tried to troubleshoot issues like mismatched impedance, coil geometry, and capacitor efficiency. This project is less about contest performance and more about re-creating the look and feel of 1950s radios while experimenting with electronics and learning through trial and error. If you’re into DIY electronics, retro crystal radios, maker projects, or hands-on science builds, join me on this journey and share your ideas in the comments—I’d love to hear from other builders, experimenters, and radio engineers!
WARNING: This project requires soldering. Soldering involves high temperatures that can cause burns and fire. Solder contains lead and other toxic chemicals. If you do not know, learn first or do not do it.
NOTES: I tried black filament and the inductance came out lower. Use low or no pigment filaments. I used pale white and white.
MATERIALS ==============================
- Space Station Shell x2
- Radar knob
- Space Station Stand (optional)
- Coil core
- Strain reliever
- Strain reliever cap
- Variable capacitor 12-170pF (aka "240pF")
- 2 mounting screws for variable capacitor
- 1 screw for radar knob/variable capacitor
- 2 screws for securing space station shell halves
- 31 AWG (0.227mm) wire
- 1n34a or D9K diode
- 20K - 40K ohm resistor
- Crystal earphone
- 2 alligator clips (antenna & ground)
- Small gauge wire/cable for antenna & ground
- Small screw to secure strain reliever cap to strain reliever
RELATED VIDEOS:
Crystal Radio--DIY Crystal Earphone youtu.be/ARtfLB0nQ5k
Crystal Radio--Basic Designing (4K) youtu.be/SSERdfAjl8g
Crystal Radio--No More Variable Capacitor Designs? (4K) youtu.be/0AvTO588SyU
========================================
VERSION 1.0 (2-3 stations)
L = 205 uH – Required inductance
D = 90mm – Diameter of coil-former
d = 0.22676 – Diameter of wire without insulation 31 AWG
k = 0.24717 – Diameter of wire with insulation Automatic
Calculate
RESULT:
N = 33.292 – number of turns
l = 8.229 mm – Length of winding
coil32.net/online-calculators/one-layer-coil-calculator.html
Var Cap: 34 to 225 pF
Original target 220 uH
RATIOS AGAINST ORIGINAL VAR CAP DESIGN xx / 130 = yyy
Wire = 31 AWG
20T 130T xx 20/130 = 0.1538461538461538 (x 33.3T === 5.1T)
30T 130T xx 30/130 = 0.2307692307692308 (x 33.3T === 7.7T)
80T 130T xx 80/130 = 0.6153846153846154 (x 33.3T === 20.5T) + 6T
Total 130T vs 33.3T
Actual: 34T === 218 uH updated to 300uH with +6T
========================================================================
VERSION 2.0 LITZ WIRE (FAILED)
coil32.net/online-calculators/one-layer-coil-calculator.html
Var Cap: 34 to 225 pF
Original tartet 220 uH, modified to 300 uH for var cap
RATIOS AGAINST ORIGINAL VAR CAP DESIGN xx / 130 = yyy
Wire = 0.04mm x 10 10/46 Litz
20T 130T xx 20/130 = 0.1538461538461538 (x 33.3T === 5.1T)
30T 130T xx 30/130 = 0.2307692307692308 (x 33.3T === 7.7T)
80T 130T xx 80/130 = 0.6153846153846154 (x 33.3T === 20.5T) + 11T + 19T === 500uH
Total 130T vs 33.3T
Actual: 34T === 300??? uH
-------------------------------
Self resonance calculator: k7mem.com/Ind_Coil_Ind_Calc.html
-------------------------------
#CrystalRadio #DIYElectronics #RetroRadio #MakerProjects
As a kid I had a "rocket radio", a small, portable crystal radio with a 1950s space theme. I've been working at recreating that. This is a capacitor tuned version. It should be able to receive 4-5 stations which is 3-4 more than the typical rocket radio. It requires both a ground and an antenna (the rocket radio just had an antenna connection.)
3D Printer Files: thingiverse.com/thing:6934296
It uses a capacitively tuned coil in the ring of a classic space station with radar tuning. We explore the challenges of coil design, impedance matching, and tuning efficiency. While the prototype currently picks up two stations, my goal is to push performance toward three, four, or even five stations through coil optimization, wire gauge experiments, and improved Q factor. We'll look at the design diagrams, adjustments, and experiments I’ve tried to troubleshoot issues like mismatched impedance, coil geometry, and capacitor efficiency. This project is less about contest performance and more about re-creating the look and feel of 1950s radios while experimenting with electronics and learning through trial and error. If you’re into DIY electronics, retro crystal radios, maker projects, or hands-on science builds, join me on this journey and share your ideas in the comments—I’d love to hear from other builders, experimenters, and radio engineers!
WARNING: This project requires soldering. Soldering involves high temperatures that can cause burns and fire. Solder contains lead and other toxic chemicals. If you do not know, learn first or do not do it.
NOTES: I tried black filament and the inductance came out lower. Use low or no pigment filaments. I used pale white and white.
MATERIALS ==============================
- Space Station Shell x2
- Radar knob
- Space Station Stand (optional)
- Coil core
- Strain reliever
- Strain reliever cap
- Variable capacitor 12-170pF (aka "240pF")
- 2 mounting screws for variable capacitor
- 1 screw for radar knob/variable capacitor
- 2 screws for securing space station shell halves
- 31 AWG (0.227mm) wire
- 1n34a or D9K diode
- 20K - 40K ohm resistor
- Crystal earphone
- 2 alligator clips (antenna & ground)
- Small gauge wire/cable for antenna & ground
- Small screw to secure strain reliever cap to strain reliever
RELATED VIDEOS:
Crystal Radio--DIY Crystal Earphone youtu.be/ARtfLB0nQ5k
Crystal Radio--Basic Designing (4K) youtu.be/SSERdfAjl8g
Crystal Radio--No More Variable Capacitor Designs? (4K) youtu.be/0AvTO588SyU
========================================
VERSION 1.0 (2-3 stations)
L = 205 uH – Required inductance
D = 90mm – Diameter of coil-former
d = 0.22676 – Diameter of wire without insulation 31 AWG
k = 0.24717 – Diameter of wire with insulation Automatic
Calculate
RESULT:
N = 33.292 – number of turns
l = 8.229 mm – Length of winding
coil32.net/online-calculators/one-layer-coil-calculator.html
Var Cap: 34 to 225 pF
Original target 220 uH
RATIOS AGAINST ORIGINAL VAR CAP DESIGN xx / 130 = yyy
Wire = 31 AWG
20T 130T xx 20/130 = 0.1538461538461538 (x 33.3T === 5.1T)
30T 130T xx 30/130 = 0.2307692307692308 (x 33.3T === 7.7T)
80T 130T xx 80/130 = 0.6153846153846154 (x 33.3T === 20.5T) + 6T
Total 130T vs 33.3T
Actual: 34T === 218 uH updated to 300uH with +6T
========================================================================
VERSION 2.0 LITZ WIRE (FAILED)
coil32.net/online-calculators/one-layer-coil-calculator.html
Var Cap: 34 to 225 pF
Original tartet 220 uH, modified to 300 uH for var cap
RATIOS AGAINST ORIGINAL VAR CAP DESIGN xx / 130 = yyy
Wire = 0.04mm x 10 10/46 Litz
20T 130T xx 20/130 = 0.1538461538461538 (x 33.3T === 5.1T)
30T 130T xx 30/130 = 0.2307692307692308 (x 33.3T === 7.7T)
80T 130T xx 80/130 = 0.6153846153846154 (x 33.3T === 20.5T) + 11T + 19T === 500uH
Total 130T vs 33.3T
Actual: 34T === 300??? uH
-------------------------------
Self resonance calculator: k7mem.com/Ind_Coil_Ind_Calc.html
-------------------------------
#CrystalRadio #DIYElectronics #RetroRadio #MakerProjects
