T6A: Basic Components – Ham Radio Technician License Study Guide

Every circuit in your radio station is built from a handful of fundamental components. Before you can understand how a transmitter works or why a filter behaves as it does, you need to know the basic parts — what each one does, how it is constructed, and what property it controls. T6A introduces these building blocks: resistors, capacitors, inductors, switches, fuses, and the batteries that power portable equipment.

These components appear in every piece of amateur radio gear. Resistors limit current, capacitors store charge, inductors store magnetic energy, switches route signals, fuses protect circuits, and batteries provide portable power. Understanding each one gives you the vocabulary to read circuit diagrams, diagnose problems, and build or modify equipment.

Resistors and Potentiometers

A resistor is the most common passive component in electronics. Its defining characteristic is that it opposes the flow of current in a DC circuit — the more resistance, the harder it is for current to flow. Resistors are rated in ohms and come in fixed values. They are used everywhere: to limit current through LEDs, to set gain in amplifiers, to create voltage dividers.

A potentiometer is a variable resistor. It has a rotating shaft or sliding element that the user can adjust, changing the resistance from near zero to the maximum rated value. The parameter a potentiometer controls is resistance. Because adjusting resistance controls current and therefore power delivered to a load, potentiometers are commonly used as volume controls in audio equipment — turning the knob changes resistance, which changes the signal level reaching the speaker.

Capacitors

A capacitor stores energy in an electric field. Physically, a capacitor consists of two conductive surfaces (called plates) separated by an insulating material called a dielectric. When voltage is applied, charge builds up on the plates and energy is stored in the electric field between them. When the voltage source is removed, the capacitor can release that stored energy back into the circuit.

Capacitors are measured in farads, though most practical values are in microfarads (µF) or picofarads (pF). They are used in power supply filters to smooth DC voltage, in RF circuits to block DC while passing AC signals, and together with inductors to form resonant circuits.

Inductors

An inductor stores energy in a magnetic field. The simplest inductor is a coil of wire — when current flows through the coil, a magnetic field forms around it, and energy is stored in that field. When the current changes or stops, the collapsing magnetic field induces a voltage that opposes the change (this is called inductance). Inductors are measured in henrys (H), with practical values often in millihenrys (mH) or microhenrys (µH).

In amateur radio, inductors appear in filters, antenna matching networks, and resonant circuits. A variable inductor (one whose inductance can be adjusted, typically by moving a ferrite core in and out of the coil) is often used in antenna tuners and transmitter output circuits.

Switches and Fuses

Switches control whether a circuit is connected or disconnected. Different switch types handle different configurations. An SPST (single-pole single-throw) switch simply opens or closes a single circuit — it has one input and one output. An SPDT (single-pole double-throw) switch connects a single circuit to one of two other circuits — one input selects between two outputs. This type is used when you want to route a signal to one of two destinations, such as switching an antenna between two radios. Figure T-2 in the exam diagrams includes a schematic symbol for an SPST switch as component 3.

A fuse is a protective device. It is placed in series with a circuit and contains a thin conductor that melts when current exceeds a safe level, permanently breaking the connection. This protects other components from damage caused by current overloads. Circuit breakers perform a similar function but can be reset rather than replaced.

Batteries

Batteries convert chemical energy into electrical energy. A critical distinction for amateur radio operators is whether a battery chemistry is rechargeable or not, since using a non-rechargeable battery in a charger can be dangerous.

Rechargeable battery chemistries include nickel-metal hydride (NiMH), lithium-ion (Li-ion), and lead-acid — all three of these can be recharged and reused. Non-rechargeable chemistries include carbon-zinc (the classic zinc-carbon "heavy duty" cell) and standard alkaline cells. Carbon-zinc is the specific non-rechargeable chemistry called out in the exam questions.

T6A Practice Questions