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Amateur Radio Info & Exams - Electronic Components

Component refresher

Resistors oppose the flow of current in any circuit, including a DC circuit. Inductors oppose current flow in an AC circuit, increasing with the frequency. While it is true that if you put an inductor in a DC circuit, and then apply power, the current will not raise instantly as it would without it. However, the question relates to the steady state, and once this occurs, the inductor has no influence.

White ceramic power resistorA 470 Ω wire-wound power resistor, rated 3 watts; J meaning 5% tolerance.
It was unsoldered from an old CRT TV.
It is in a ceramic case. Lead spacing is 0.2" = 5.08 mm.
Many have a lead at each end. In either case, the element is held in place by cement.

A potentiometer is a specific kind of variable resistor, often used as a volume control.

A capacitor stores energy in the electric field in the insulating layer or air between the plates. They are also handy, as they can pass an AC (audio or RF) signal while blocking DC, and so are often used between stages of an amplifier.

Two axial 10 microhenry, 3 amp inductors
An inductor showing the wire coil, wrapped over an iron powder core. The value is 10 microhenries, and the current rating is 3 amps. The DC resistance is 77mΩ.
The core is 18 mm long.

An inductor stores energy in a magnetic field, within the coil of wire they are normally made from. They are also used when you want to pass DC or low frequency (AC) power into a feed-line, or extract it to run a pre-amplifier at the the top of your mast, while blocking RF from entering the power supply.

Two axial 10 microhenry, 3 amp inductors
An inductor showing the wire coil, wrapped over an iron powder core. The value is 10 microhenries, and the current rating is 3 amps. The DC resistance is 77mΩ.
The core is 18 mm long. Components with a lead at each end is termed "axial", as it appears to run through its axis.
A radial inductor
Another inductor showing the wire coil, pulled from a CRT TV.
The spacing of the "radial" leads is 0.2", or 5.08 mm.

The simplest semiconductor device is the diode, which allows current to flow from the plain end to the banded one, but not in reverse. Flow is Anode (A) to Cathode (K). Both regular and zener diodes vary from tiny to huge stud mounted (affixed with a large nut, and connected with a cable over 5mm thick), and hockey-puck sized devices.

The standard transistor, also called a bipolar junction transistor (BJT), consists of three layers of semiconductor material, usually silicon these days, but germanium in the past, or a few special applications. The exams just calls these a "transistor". Transistors require current to flow into (or from) the Base to operate, up to a twentieth of the collector to emitter current used to operate the load.

The transistors ability to amplify is called its gain. Within a single part-number this can vary over a wide range, so surrounding circuitry is often designed to manage this, or at least take it into account.

In the FET, or field effect transistor, conventional current flows from drain to source (note electrons flow the other way). Voltage on the gate controls the current flow. These are also called unipolar transistors. Gate current is super-low (often picoamps).

(The BJT and FET terminal names have been removed from the exam.)

Off the exams, but perhaps handy to know if buying parts, resistors, capacitors, and inductors are termed "passive" components, or "passives". Those with an input which influences current flow in other parts are termed "active" components, including all classes of transistors, and ICs. You will notice that the latter are semiconductors, but valves are also active devices. Diodes vary in their classification.

Unless defined otherwise, a switch is a mechanical device with physically connects or disconnects the circuit. The big old knife switches in Frankenstein style movies demonstrate this.

Cells and Batteries

There are two families of batteries, non-rechargeable (consisting of primary cells) and rechargeable (consisting of secondary cells).

The non-rechargeable in the exam is the carbon-zinc, the standard 1.5 volt cell, actually somewhat rare. An improved version, containing chloride in the electrolyte sold as "heavy-duty" or "extra heavy-duty", or "super heavy-duty". Despite the spin, these have considerably less capacity than the alkaline or "alkaline-manganese" battery. In the carbon-zinc, the case is the zinc negative electrode, and the acid electrolyte eats away the case as the battery is used, and if they are left in a device for an extended period, with corrode through, and damage the device. Alkaline is much more suitable for using in AA cell cases available for some HTs. Off the exam, some radios use lithium coin cells (3 volt), or silver-oxide cells, to maintain the memory.

Used cells should be placed in the bins at Aldi, as the metals, especially zinc, should not go to landfill.

Rechargeable: Motor vehicles use lead-acid batteries to start the car, and to operate accessories when the ignition is off. They also smooth the pulsing or rippled DC from the alternator. Standard automotive batteries are not suitable for running equipment for extended periods; but "deep cycle" and some marine batteries are. Lead-acid gel-cell (also called AGM) is a variation, handy for mountain-top operating.

Nickel-cadmium and Nickel-metal hydride are often in dry-cell formats, or in battery-packs in older hand-helds. There are also liquid Ni-Cad batteries, which can last many decades if looked after.

A more recent addition is the Lithium-ion cell, used as single cells in pocket sized HTs, and as two cell batteries in larger models. 14.4 volt four cell ones, designed for RC uses, are also being used by the Summits-on-the-Air brigade to power 12 volts radios.

Often enclosed in glass, ceramic, or plastic, fuses consist of a thin wire, or stamped sheet metal, which melts or vaporises when an excessive current flows through it. A mirrored glaze inside the glass means the fuses end was the result of a serious short or surge; small balls at the ends of the remaining wires means a much less serious overload.

Relevant Questions

These are the actual questions relating to the information above.

What electrical component is used to oppose the flow of current in a DC circuit?
A. Inductor
B. Resistor
C. Voltmeter
D. Transformer

In a steady-state DC circuit only a resistor opposes (or reduces) current flow, so circle answer B.

What type of component is often used as an adjustable volume control?
A. Fixed resistor
B. Power resistor
C. Potentiometer
D. Transformer

This is the "Pot", or potentiometer, answer C.

What electrical parameter is controlled by a potentiometer?
A. Inductance
B. Resistance
C. Capacitance
D. Field strength

While it may affect another real world function, the electrical parameter is resistance, answer B.

What electrical component stores energy in an electric field?
A. Resistor
B. Capacitor
C. Inductor
D. Diode

This is the capacitor, answer B. Capacitors store energy in an insulator, between plates.

What type of electrical component consists of two or more conductive surfaces separated by an insulator?
A. Resistor
B. Potentiometer
C. Oscillator
D. Capacitor

The symbol for a capacitor is two plates with an air-gap insulator, so answer D. We physically see these plates in the large old tuning capacitors, also used in some antenna tuners.

What type of electrical component stores energy in a magnetic field?
A. Resistor
B. Capacitor
C. Inductor
D. Diode

This is the inductor, answer C. An inductor is a coil, and we relate coils to electro-magnets.

What electrical component is usually composed of a coil of wire?
A. Switch
B. Capacitor
C. Diode
D. Inductor

The symbol for the inductor looks like a coil of wire, answer D. You also saw this in the image above.

What electrical component is used to connect or disconnect electrical circuits?
A. Magnetron
B. Switch
C. Thermistor
D. All of these choices are correct

A switch physically connects or disconnects the circuit, answer D. Others are not relevant.

What electrical component is used to protect other circuit components from current overloads?
A. Fuse
B. Capacitor
C. Inductor
D. All of these choices are correct

A fuse "blows", or goes open-circuit when excessive, potentially damaging, current flows, answer A.

Which of the following battery types is rechargeable?
A. Nickel-metal hydride
B. Lithium-ion
C. Lead-acid gel-cell
D. All of these choices are correct

All are rechargeable, and have application in Ham radio, so answer D.

Which of the following battery types is not rechargeable?
A. Nickel-cadmium
B. Carbon-zinc
C. Lead-acid
D. Lithium-ion

Þe aulde Carbon-zinc, often sold as "Heavy Duty", is non-rechargeable, also called a "primary cell". Answer B gets you the Banana!

What class of electronic components is capable of using a voltage or current signal to control current flow?
A. Capacitors
B. Inductors
C. Resistors
D. Transistors

Current (driven by a voltage) going into the Base of a transistor allows current to flow from Collector to Emitter, answer D. (Note the flow is reverse in PNPs.) In a FET it is the presence of a voltage which operates the device, with very little control current needed.

What electronic component allows current to flow in only one direction?
A. Resistor
B. Fuse
C. Diode
D. Driven Element

This is the diode, answer C. --|>|--

Which of these components can be used as an electronic switch or amplifier?
A. Oscillator
B. Potentiometer
C. Transistor
D. Voltmeter

The only applicable device here is the Transistor, answer C. Note that an oscillator is a multi-component device.

Which of the following components can be made of three layers of semiconductor material?
A. Alternator
B. Transistor
C. Triode
D. Pentagrid converter

This is the transistor, the only solid state device here, answer B. The lower two are thermionic valves / electron tubes. The first is the generator in your (modern) car.

Which of the following electronic components can amplify signals?
A. Transistor
B. Variable resistor
C. Electrolytic capacitor
D. Multi-cell battery

The transistor is the only amplifying device listed here, so answer A.

How is the cathode lead of a semiconductor diode often marked on the package?
A. With the word cathode
B. With a stripe
C. With the letter C
D. With the letter K

A diode's cathode is are most usually identified with a band, matching the bar on the symbol, answer B. On big diodes, a diode symbol may be used, or very occasionally, a K. The stripe, B, is however most often used.

What does the abbreviation LED stand for?
A. Low Emission Diode
B. Light Emitting Diode
C. Liquid Emission Detector
D. Long Echo Delay

It is a diode which emits light, so answer B, light emitting diode. The rest are silly.

What does the abbreviation FET stand for?
A. Field Effect Transistor
B. Fast Electron Transistor
C. Free Electron Transmitter
D. Frequency Emission Transmitter

It is the Field Effect Transistor, answer A. The rest of the terms are nutty.

What are the names of the two electrodes of a diode?
A. Plus and minus
B. Source and drain
C. Anode and cathode
D. Gate and base

These are the anode and cathode (A & K), answer C. You may recognise these from electro-chemistry too.

Which of the following could be the primary gain-producing component in an RF power amplifier?
A. Transformer
B. Transistor
C. Reactor
D. Resistor

If a valve / tube is not used, some form of transistor would be, answer B. This may be an LDMOS (laterally diffused metal oxide semiconductor) FET.

What is the term that describes a transistor's ability to amplify a signal?
A. Gain
B. Forward resistance
C. Forward voltage drop
D. On resistance

This is its gain, answer A.

On to: Electrical Units & Metric Multipliers

You can find links to lots more on the Learning Material page.

Written by Julian Sortland, VK2YJS & AG6LE, February 2018.

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