Reverse Choke Calculator
Enter what you have on hand, see what you can build
📊 Analysis Results
Core Size
FT240
Ferrite Mix
Type 43
AL Value
1075 nH/t²
Inner Diameter
1.40"
Max Turns
12
📏 Wire Fit Analysis
With RG-8X (0.24" OD) on FT240-43, you can fit approximately 12-14 turns single-layer around the inner diameter.
Estimated Choking Impedance by Band
| Band | Freq (MHz) | 8 turns | 10 turns | 12 turns | 14 turns |
|---|
🟢 Excellent (>5000Ω) 🔵 Good (2000-5000Ω) 🟡 Marginal (1000-2000Ω) 🔴 Poor (<1000Ω)
Recommended Configurations
📚 Data Sources & Credits
- Complex Permeability Data: Fair-Rite Corporation published material datasheets (Types 31, 43, 61)
- AL Values & Core Dimensions: toroids.info toroid database
- Calculation Methodology: VK3CPU RF Toroid Calculator by Miguel VK3CPU
- Choke Design Research: K9YC's "A Ham's Guide to RFI"
- Additional Research: G3TXQ's ferrite studies, Palomar Engineers application notes
- Wire Specifications: PowerStream AWG tables
- Magnet Wire Data: MWS Wire heavy build specs (NEMA MW 1000)
- Coax Specifications: Cooner Wire and manufacturer datasheets
Note: Impedance calculations are estimates based on published complex permeability data. Actual results may vary ±20% due to manufacturing tolerances, winding technique, and measurement conditions. For critical applications, verify with a VNA.