In this post we provide a calculator with an example. Additionally we provide an explanation of RF chokes and their applications
Contents
Calculator
Enter
- Impedance Value for the choke (default value is 500 Ω or ten times the characteristic impedance of 50 Ω)
- Frequency of operation
The tool will provide the inductance value for the choke
Example Calculation
If we use an impedance value of 500 ohm at a frequency of 2000 MHz, the value of the choke is 39.8 nH.
At 3 GHz, the inductance value drops to 26.5 nH.
Background
What is a choke?
An RF (Radio Frequency) choke, also known as a choke coil or simply a choke, is an electrical component used to block or filter out high-frequency signals while allowing direct current (DC) or low-frequency signals to pass through. Wikipedia Reference.
Essentially a choke is an inductor. An example is shown in the picture below.
RF chokes are primarily used in applications involving radio frequency or other high-frequency signals to prevent unwanted interference or to create impedance matching.
RF chokes are typically constructed as coils of wire wound around a magnetic core, although some chokes may be air-core, depending on the application. The coil of wire in the choke creates inductance, which resists changes in the flow of current. This inductance is effective at impeding the flow of high-frequency AC signals, effectively blocking them or attenuating their amplitudes, while DC or low-frequency signals pass through with minimal impedance.
Applications
Common uses of RF chokes include:
- Noise suppression: RF chokes are often used in power supply circuits to filter out high-frequency noise and electromagnetic interference (EMI). They help reduce voltage ripple and improve the stability of the DC power supply.
- Antenna matching: In RF circuits and radio transmitters, RF chokes can be used to match the impedance of the antenna to that of the transmitter or receiver, ensuring maximum power transfer.
- Balun applications: RF chokes are used in baluns (balanced-unbalanced transformers) to provide impedance transformation between balanced and unbalanced transmission lines.
- RF filtering: They are used in RF filter networks to create bandpass, bandstop, or low-pass filters for specific frequency ranges. A series inductor in the pi low pass filter acts as a choke.
- RF isolation: RF chokes can provide isolation between different parts of a circuit to prevent interference or feedback between them.
RF chokes come in various shapes and sizes, with different inductance values and current ratings, to suit different applications. The choice of an RF choke depends on the specific requirements of the circuit and the frequency range of interest.