is an inductor
designed to have a high reactance
to a particular frequency when used in a signal-carrying circuit.
Choke coils are inductances that isolate AC
frequency currents from certain areas of a radio circuit. Chokes depend upon the property of self-inductance
for their operation. They are used to block alternating current
while passing direct current
(contrast with capacitor
). Common-mode choke coils are useful in a wide range of prevention of electromagnetic interference
(EMI) and radio frequency interference
(RFI) from power supply
lines and for prevention of malfunctioning of electronic equipment.
Types and construction
Chokes used in radio circuits are divided into two classes – those designed to be used with audio frequencies
, and the others to be used with radio frequencies
. Audio frequency coils
, usually called A.F. chokes, can have ferromagnetic iron
cores to increase their inductance. Chokes for higher frequencies (ferrite chokes
or choke baluns
) have ferrite
cores. Chokes for even higher frequencies have air cores. Radio frequency
coils, (R.F. chokes), usually don't have iron cores. In high power service so much heat would be produced in making and destroying the field in the core that the coil would burn up.