Uploaded January 2025 | Updated September 2026, 2 weeks ago
We are running experiments to see why the bobbin windings in a capacitively tuned crystal radio did not work. There was almost no sound. This round we are checking the effects of smaller diameter coil cores.
We are starting with a known, working coil and 1 by 1 varying the parameters that were changed with the bobbin coils:
-- Wire diameter, straight wind (video #1)
-- Core size
-- Winding type (straight 1 layer vs. multi-layer scatter)
KNOWN STANDARD COIL:
- Wire size big: 0.81mm (20 AWG)(Done/standard) Straight wound
- Core: 42 mm (1.65") PVC plastic
- Inductance total: 205 uH
- Taps: 0T, 20T, 30T, 80T
EXPERIMENTAL COIL:
coil32.net/online-calculators/one-layer-coil-calculator.html
- Wire size fine: 0.227mm (31 AWG)(Done/standard) Straight wound
- Core: 8 mm (x") PLA plastic
- Inductance total: 205 uH Target (207 measured)
ENTER THE INPUT DATA:
L = 205 uH – Required inductance
D = 8 mm – Diameter of coil-former circumference = 25.13 mm
d = 0.227 mm – Diameter of wire without insulation 31 AWG
k = 0.24717 – Diameter of wire with insulation
RESULT:
N = 780.822 – number of turns
l = 192.997mm – Length of winding
Length of wire = 25.13mm x 780.822T = 19,622.05686mm or 19.6 meters
- 20T / 130T = 0.1538461538461538 (x 780.822T = 120.1265T) (x 19.6 m = 3.01539 m)
- 30T / 130T = 0.2307692307692308 (x 780.822T = 180.19T) (x 19.6 m = 4.5231 m)
- 80T / 130T = 0.6153846153846154 (x 780.822T = 480.5058T) (x 19.6 m = 12.0615 m)
BOBBIN COIL (capacitively tuned version):
- Wire size fine: 0.227mm (31 AWG)(Done/standard) Multi-Layer Scatter Wound
- Core: 8 mm (1.65") plastic
- Inductance total: 219 uH
- Taps: 0T, 10T, 15T, 40T
RELATED VIDEOS:
Crystal Radio--The Bobbin Inductors Fail. But WHY? 2/2
youtu.be/iH66WckUzFE
Crystal Radio--No More Small Core Inductors??? Maybe. 1/2
youtu.be/CJlAwvE5p7g
Crystal Radio--Cheap & Easy Inductor From Sewing Machine Bobbin
youtu.be/ecuhAiBYJzs
1 Capacitor Crystal Radio--No More Variable Capacitor Designs? (4K)
youtu.be/0AvTO588SyU
We are running experiments to see why the bobbin windings in a capacitively tuned crystal radio did not work. There was almost no sound. This round we are checking the effects of smaller diameter coil cores.
We are starting with a known, working coil and 1 by 1 varying the parameters that were changed with the bobbin coils:
-- Wire diameter, straight wind (video #1)
-- Core size
-- Winding type (straight 1 layer vs. multi-layer scatter)
KNOWN STANDARD COIL:
- Wire size big: 0.81mm (20 AWG)(Done/standard) Straight wound
- Core: 42 mm (1.65") PVC plastic
- Inductance total: 205 uH
- Taps: 0T, 20T, 30T, 80T
EXPERIMENTAL COIL:
coil32.net/online-calculators/one-layer-coil-calculator.html
- Wire size fine: 0.227mm (31 AWG)(Done/standard) Straight wound
- Core: 8 mm (x") PLA plastic
- Inductance total: 205 uH Target (207 measured)
ENTER THE INPUT DATA:
L = 205 uH – Required inductance
D = 8 mm – Diameter of coil-former circumference = 25.13 mm
d = 0.227 mm – Diameter of wire without insulation 31 AWG
k = 0.24717 – Diameter of wire with insulation
RESULT:
N = 780.822 – number of turns
l = 192.997mm – Length of winding
Length of wire = 25.13mm x 780.822T = 19,622.05686mm or 19.6 meters
- 20T / 130T = 0.1538461538461538 (x 780.822T = 120.1265T) (x 19.6 m = 3.01539 m)
- 30T / 130T = 0.2307692307692308 (x 780.822T = 180.19T) (x 19.6 m = 4.5231 m)
- 80T / 130T = 0.6153846153846154 (x 780.822T = 480.5058T) (x 19.6 m = 12.0615 m)
BOBBIN COIL (capacitively tuned version):
- Wire size fine: 0.227mm (31 AWG)(Done/standard) Multi-Layer Scatter Wound
- Core: 8 mm (1.65") plastic
- Inductance total: 219 uH
- Taps: 0T, 10T, 15T, 40T
RELATED VIDEOS:
Crystal Radio--The Bobbin Inductors Fail. But WHY? 2/2
youtu.be/iH66WckUzFE
Crystal Radio--No More Small Core Inductors??? Maybe. 1/2
youtu.be/CJlAwvE5p7g
Crystal Radio--Cheap & Easy Inductor From Sewing Machine Bobbin
youtu.be/ecuhAiBYJzs
1 Capacitor Crystal Radio--No More Variable Capacitor Designs? (4K)
youtu.be/0AvTO588SyU
