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Calcimator

Antenna Trap Design Calculator

Calculate trap capacitor and inductor values for multi-band wire antennas. Includes coil winding data and impedance analysis.

Inputs

MHz
μH
in

Results

Required Capacitance

50.6 pF

Trap Impedance (Q=200)

44,454 Ω

Coil Turns

7.6

Inductive Reactance222.27 Ω
Capacitive Reactance222.27 Ω
Wire Length for Coil5 ft
Turn Spacing0.328 in
Trap Bandwidth (3 dB)0.071 MHz
How to Use This Calculator
  1. Enter the trap resonant frequency (MHz) matching the band you want to isolate.
  2. Set the coil inductance (µH) and coil form diameter (mm) for your wound coil.
  3. Review required capacitance (pF), inductive reactance (Ω), and number of coil turns needed.
  4. Use the trap impedance output to verify the trap will effectively isolate the outer section.
  5. Wind the coil to the calculated turns and trim the capacitor to achieve resonance.

How the result changes with Trap Frequency

Trap FrequencyRequired CapacitanceTrap Impedance (Q=200)Coil Turns
513.9 pF160,221 Ω7.6
1760.33 pF552,920 Ω7.6
3250.1 pF1,021,018 Ω7.6
4500.05 pF1,413,717 Ω7.6

What each input means

Trap Frequency
Frequency at which the trap should resonate (isolates antenna sections)
Coil Inductance
Desired coil inductance (higher = fewer turns but larger capacitor needed)
Coil Form Diameter
Diameter of the coil form (PVC pipe, etc.) in inches

How this is calculated

Formula

C = 1 / ((2πf)² × L); Turns via Wheeler's formula

Worked example, using the default values

  1. Identify Input Parameters
    Trap Frequency = 14.15, Coil Inductance = 2.5, Coil Form Diameter = 2.5 = 3 input(s) provided
  2. Calculate Required Capacitance
    Required Capacitance
    50.6 = 50.6
  3. Calculate Trap Impedance
    Trap Impedance
    44454 = 44454
  4. Calculate Coil Turns
    Coil Turns
    7.6 = 7.6
  5. Calculate Inductive Reactance
    Inductive Reactance
    222.27 = 222.27
  6. Calculate Capacitive Reactance
    Capacitive Reactance
    222.27 = 222.27

Engine last updated . Checked against 1 independently-derived test — how we verify calculators.

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