Enter the target resonant frequency and either the trap inductance or capacitance into the calculator. It will compute the missing value for an ideal LC antenna trap (resonant circuit).

Antenna Trap Calculator

Enter any two values to calculate the third

Related Calculators

Antenna Trap Formula

L_{\mu H} = \frac{25330}{f_{MHz}^{2}\,C_{pF}}

Variables:

  • L is the trap inductance (μH)
  • f is the resonant frequency (MHz)
  • C is the trap capacitance (pF)

To calculate the inductance of an ideal LC antenna trap at a target resonant frequency, you must know (or choose) the trap capacitance. Then compute L by dividing 25330 by f2 × C (using MHz, pF, and μH).

How to Calculate Antenna Trap?

The following steps outline how to calculate an ideal LC antenna trap value.

  1. First, determine the desired resonant frequency of the trap (MHz).
  2. Next, determine the other component value (either capacitance in pF or inductance in μH).
  3. Then, use the LC resonance relationship to compute the missing value (for example: LμH = 25330 / (fMHz2·CpF)).
  4. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

frequency (MHz) = 7, capacitance (pF) = 100 ⇒ inductance (μH) = 25330 ÷ (72 × 100) ≈ 5.17

FAQs

What is an Antenna Trap?

An Antenna Trap is a parallel LC (inductor and capacitor) resonant circuit that is typically placed in series with an antenna element. At its resonant frequency it presents a high impedance, which helps isolate sections of the antenna so it can operate on multiple bands.

Why is the frequency in MHz for calculating the Antenna Trap?

You can use any frequency unit as long as you use consistent units in the formula. MHz is commonly used for HF/VHF antenna work and pairs conveniently with μH and pF in the common rule-of-thumb form of the resonance equations. (For reference, the radio frequency spectrum is often defined as 3 kHz to 300 GHz.)

How can I improve the efficiency of my antenna?

Improving antenna efficiency can involve several strategies, including optimizing the antenna design for your specific application, ensuring the antenna is correctly tuned to the desired frequency, reducing losses by using quality materials, and minimizing obstructions in the antenna’s near field.

Can the Antenna Trap formula be used for any type of antenna?

The resonance relationship is a general LC circuit result and applies to antenna traps in many antenna types. However, real traps are affected by coil self-capacitance, stray capacitance, component tolerances, and losses (Q), so practical designs often require measurement and adjustment after initial calculations.