I. Classification of Inductors According to the form of inductance: fixed inductors, variable inductors. According to the properties of the magnetic material: air core coil, ferrite core coil, iron core coil, copper core coil. According to the operating properties: antenna coil, oscillating coil, choke coil, trap coil, deflection coil. According to the winding structure: single-layer coil, multi-layer coil, honeycomb coil.

II. Main characteristic parameters of inductor coils

1. Inductance L Inductance L represents the inherent characteristics of the coil itself, independent of the current magnitude. Except for special inductor coils (color code inductors), inductance is generally not specifically marked on the coil, but is labeled with specific names.

2. Reactance XL The magnitude of the impedance of an inductor coil to alternating current is called reactance XL, measured in ohms. It is related to inductance L and the frequency of the alternating current f as XL=2πfL.

3. Quality factor Q The quality factor Q is a physical quantity that represents the quality of the coil. Q is the ratio of reactance XL to its equivalent resistance, i.e., Q=XL/R. The higher the Q value of the coil, the lower the loss in the circuit. The Q value of the coil is related to factors such as the DC resistance of the conductor, dielectric losses of the core, losses caused by shielding or iron core, and the influence of high-frequency skin effect. The Q value of the coil is usually in the range of tens to hundreds.

4. Distributed capacitance The capacitance existing between turns of the coil, between the coil and the shield, and between the coil and the base plate is called distributed capacitance. The presence of distributed capacitance reduces the Q value of the coil, deteriorating its stability. Therefore, the smaller the distributed capacitance of the coil, the better.

III. Commonly used coils

1. Single-layer coil: A single-layer coil is wound with insulated wire coil by coil on a paper tube or rubber frame. An example is the wave antenna coil in a transistor radio.

2. Honeycomb coil: If the coil being wound does not lie parallel to the rotating surface but intersects at a certain angle, it is called a honeycomb coil. The number of times the wire bends back and forth in one rotation is often referred to as the number of folding points. The advantage of honeycomb winding is that it has a small volume, low distributed capacitance, and a large inductance. Honeycomb coils are typically wound using a honeycomb winding machine, and the more folding points, the smaller the distributed capacitance.

3. Ferrite core and iron powder core coils: The inductance of the coil is related to the presence of a magnetic core. Inserting a ferrite core into an air core coil can increase the inductance and improve the quality factor of the coil.

4. Copper core coil: Copper core coils are widely used in the ultra-short wave range. The position of the rotating copper core is used to change the inductance, making the adjustment convenient and durable.

5. Color code inductors: Color code inductors have a fixed inductance value, and their inductance is marked using color bands similar to resistors.

6. Choke coil: A coil that restricts the flow of alternating current is called a choke coil, which can be high-frequency choke coils or low-frequency choke coils.

7. Deflection coil: The deflection coil is the load of the output stage of the television scanning circuit. The deflection coil requires high deflection sensitivity, uniform magnetic field, high Q value, small volume, and low cost.

Inductor classification: Large inductors are all wound, and they can be classified into air core inductors and magnetic core inductors based on their structure. Air core inductors have good linearity but are severely affected by external interference, while magnetic core inductors exhibit saturation phenomena, and the bending of the magnetization curve results in an unstable inductance value.

Other inductors are classified as fixed inductors and variable inductors. Fixed inductors include small magnetic rings, small lead wires, etc., while variable inductors include mid-range inductors, which are used in detection and transmission circuits and must be shielded to overcome interference. Inductors with frames are also a type of wound inductor, where the frame provides structural support. If the frame is a magnetic core, it becomes a magnetic core inductor.