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Is an RF Choke the Same As a Balun?

An RF choke prevents unwanted radio frequency signals from entering other circuits in many electronic applications. A balun matches the impedance of balanced and unbalanced circuits for applications in almost all fields of electronics. Ham radio operators use a circuit called a choke balun that combines both functions into one operation. But an RF choke and a balun are two entirely different things.

RF Choke
- In any electronics circuit a choke is an inductor or coil of wires that filters out unwanted alternating circuit signals. Most commonly, a choke filters AC hum or ripple out of the output of a direct current power supply. When filtering radio frequencies out of any circuit, the choke is called an RF choke. The frequencies a choke filters out depend on the value of the inductor, expressed in henrys. Generally speaking, the lower the inductance rating, the higher the frequency it will filter. But specific details of an RF choke design depend on many different circuit characteristics.
Balun
- The word balun comes from a combination of the words balanced and unbalanced. A balanced signal travels on a pair of wires, with each conductor carrying equal amounts of energy. An unbalanced signal travels on a coaxial cable, with all the energy on a single center conductor and an outer shield connected to ground to prevent interference. A balun joins the energy of the two sides of a balanced signal to change it to unbalanced, or separates an unbalanced signal into two equal parts to make it balanced. A balun may also match the impedance of the circuits it connects.
Impedance
- Impedance measures how much a circuit or wire opposes or restricts an electronic signal. Complex electronic formulas calculate impedance considering DC resistance expressed in ohms, electronic capacitance expressed in farads and inductance expressed in henrys. Cables that use wire pairs and coaxial cables are also designed with specific impedance characteristics. For electronic connections, the impedance of the wire or cable should match the impedance of the circuits they connect. An impedance mismatch can cause signal loss and distortion. Certain types of baluns also match the impedance of circuits to the wires or cables that connect them.
Choke Balun
- A choke balun used on a coaxial cable to a ham radio antenna uses some of the characteristics of both theories. Simply put, the choke action is meant to concentrate all the power into the antenna and reduce the amount of energy that can return to the transmitter on the center conductor of the cable. The balun action is meant to prevent any portion of the signal from returning to the transmitter case on the shield. Ham radio operators and antenna manufacturers disagree on the effectiveness of choke baluns, and many antenna manufactures say they are not needed.

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