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Amateur Radio Info & Exams - Components 1 - Batteries, Diodes, Transistors

This covers a range of components used in Ham radio.

Maths Comment

One or more small or subscript character(s) may be appended to a parameter to indicate what it relates too. VBE or VBE; or ICE are examples. These are the base to emitter voltage and collector to emitter current.


A "battery" is an assembly of two or more electro-chemical cells, which convert chemical potential energy into electromotive force.

Rechargeable batteries are often used in Amateur radio. The lead-acid battery, especially the 12 volt version, with 14 volts on charge, will power a 100 watt mobile rig at a "field day" events, or during power failures, and during disasters, additional units can be recovered from tsunami or flood damaged vehicles. They have six cells. Assuming we wish to take these home and recharge them for the next event, they should not be discharged below 10.5 volts. In any case, the connected radios will likely perform poorly at this point.

One magazine article suggested using specially sourced seven cell batteries which have a 14 volt output while not being charged.

Older hand-held and similar radios can be powered from NiCad (Nickel Cadmium) batteries. These have the benefit of high current output for their size, thanks to their low internal resistance. For the same reason, these were also used in remote-controlled cars. A development is the NiMH (Nickel - Metal Hydride) cell, often with a greater capacity. In both cases it is possible to replace cells in battery packs, or to buy replacement packs with greater capacity than the original.

Old-fashioned zinc-carbon cells should not be recharged. I believe they can burst as there is no provision for gases created to escape, but they are also subject to leakage, as the zinc case is also the electrode, and it is likely that they case would be perforated by subsequent discharges. In many cases Alkaline batteries and cells are far better value that any with "Heavy Duty" in their name, which are zinc chloride cells.

Off the exam, various lithium-ion technologies are used in modern handhelds, while lithium-ion remote control vehicle packs are an option for powering mobile radios on mountain top exercises.

Electric vehicle development may lead to some new technologies. One may be aluminium-ion. At 2.65 volts per cell, five in series would provide a useful 13.25 volts.

Solid state diodes

There are two common semiconductor materials used for signal and power diodes. The material affects the voltage at which the diodes conduct forward current. Historically, Germanium was used, for diodes and transistors. The benefit is that the forward voltage is low, 0.3 volts according to the examiners. For the modern silicon diodes, the drop is 0.7 volts. These devices are however more rugged.

Schottky Diodes

The Schottky diode is an improved diode, with one benefit being reduced capacitance, important for RF switching. Switching RF signals using diodes is done by biasing the diode to conduct, or not, using DC voltages.


As you would probably know, transistors can be used as a linear device, amplifying audio or RF signals. However, you would remember back to the Technician paper, where a transistor was used to switch a lamp. Related to this is using transistors in logic circuits, where they are switched between the saturated (fully conducting) and cut-off (open / off) modes.

Saturation is achieved by ensuring the base to emitter current is several times that required to ensure the lowest gain samples of the transistor used will cause the collector to emitter current necessary to pull the collector close to the negative rail. If we have a 12 volt rail, and a 2 kΩ resistor rail to collector, then 6mA could flow. If the resistors gainis 50 to 250, then we need several times 0.12 to flow from base to emitter, say 0.5 mA is fine. If the on voltage of the input is 6 volts, allow a generous 1 volt for VBE, and we want 0.5mA through a resister with 5 volts across it, so 10,000 is the maximum resistor value. To ensure the transistor is off, we must make sure less than 0.6 volts is present at the base when we wish the transistor not to conduct.


Field effect transistors are a family of devices with high input impedance. One kind had a metal gate insulated from the main silicon "channel" by a thin layer of silicon oxide, and this sandwich gives the name: metal, oxide, semiconductor - MOSFET.

Resistors - Temperature Coefficient

As most components are heated or cooled, their characteristics change, often in a fairly predictable manner. For resistors this can be an increase or a decrease, depending on the material used. Often this variation is not an issue, say just changing a power supply's voltage by a small fraction of a volt. For things like oscillators it is a problem, but can be mitigated by things like turning mains powered test equipment on half-an-hour before using it, or using equipment with the crystal in an internal "oven" which maintains it at a specific temperature. At other times the characteristic can be used to make a sensor for a thermometer, current limiting devices, or a temperature compensation circuit.

Metal film resistors may have a 6th band, indicating "TC", or that may be available on a data-sheet.

Off the exam, metals, and thus metal film and wire-wound resistors have a positive coefficient; and carbon, germanium, and silicon has a negative coefficient, so the carbon film and carbon composition resistors have a negative coefficient.


These consist or coils of wire, usually enamelled copper wire. While they can air cored, winding them onto a core of ferrite or iron powder is common, with a toroidal shape being popular. This form allows high inductance in a small space, and tends to contain the field withing the core. Ferrite is an iron-oxide base material, and different ferrite blends are available, with different characteristics, used at different frequencies. Manganese-zinc ferrite and Nickel-zinc ferrite are examples. Air-cored inductors on a ceramic or plastic former may use stiff uninsulated wire or metal strip. Traces on a printed circuit board can be used as inductors. Note that an inductor can be a single loop, or even just a U-shaped wire.

When any two wires are in proximity there is some capacitance between them. This includes in an inductor. Thus, as the frequency of a signal accross or passing through an inductor rises there is a point where the inductance and capacitance cause the same reactance the inductor becomes "self-resonant". Above this the capacitive aspect becomes prominent.

Off the exam, a "hair-pin" shaped wire can be used as a parallel resonant circuit at several hundred MHz.


There are many different materials used to make capacitors. An example is the ceramic capacitor, suitable for less demanding RF applications, and very low in cost.

Relevant Questions

These are actual questions from the General exam pool.

What is the minimum allowable discharge voltage for maximum life of a standard 12 volt lead acid battery?
A. 6 volts
B. 8.5 volts
C. 10.5 volts
D. 12 volts

These batteries should not be discharged below 10.5 volts, answer C.

G6A02 (B)
What is an advantage of the low internal resistance of nickel-cadmium batteries?
A. Long life
B. High discharge current
C. High voltage
D. Rapid recharge

NiCads are capable of high discharge current, answer B.

What is the approximate junction threshold voltage of a germanium diode?
A. 0.1 volt
B. 0.3 volts
C. 0.7 volts
D. 1.0 volts

These diodes have a low forward voltage, around 0.2 or 0.3 volts, depending on the forward current, answer B.

Which of the following is an advantage of an electrolytic capacitor?
A. Tight tolerance
B. Much less leakage than any other type
C. High capacitance for a given volume
D. Inexpensive RF capacitor

They have a fairly high capacitance for their volume, making them suitable for filtering mains powered supplies, answer C.

What is the approximate junction threshold voltage of a conventional silicon diode?
A. 0.1 volt
B. 0.3 volts
C. 0.7 volts
D. 1.0 volts

These are listed at between 0.6 and 0.7 volts answer C.

Which of the following is a reason not to use wire-wound resistors in an RF circuit?
A. The resistor's tolerance value would not be adequate for such a circuit
B. The resistor's inductance could make circuit performance unpredictable
C. The resistor could overheat
D. The resistor's internal capacitance would detune the circuit

Inductors are also wound from wire, so a wire-wound resistor would likely have inductance which would affect the operation of the circuit, answer B.

What are the stable operating points for a bipolar transistor used as a switch in a logic circuit?
A. Its saturation and cutoff regions
B. Its active region (between the cutoff and saturation regions)
C. Its peak and valley current points
D. Its enhancement and depletion modes

Logic circuits operate with the transistor at either saturation and cutoff regions, answer A.

Saturation means the transistor is fully on, and cutoff means fully off.

What is an advantage of using a ferrite core toroidal inductor?
A. Large values of inductance may be obtained
B. The magnetic properties of the core may be optimized for a specific range of frequencies
C. Most of the magnetic field is contained in the core
D. All these choices are correct

An inductor wound on a "donut" of ferrite has all these advantages, answer D.

Which of the following describes the construction of a MOSFET?
A. The gate is formed by a back-biased junction
B. The gate is separated from the channel with a thin insulating layer
C. The source is separated from the drain by a thin insulating layer
D. The source is formed by depositing metal on silicon

MOSFETs have a gate which is insulated from the channel. The "MOS" term refers to the layering of the metal (often aluminium) gate, the insulating silicon oxide, then the semiconductor layers. Answer B.

Which element of a triode vacuum tube is used to regulate the flow of electrons between cathode and plate?
A. Control grid
B. Heater
C. Screen Grid
D. Trigger electrode

Regulate? Control! Yep, similar meanings, and control grid is correct answer. In a TRIode, this is the only grid, so definitely answer A.

What happens when an inductor is operated above its self-resonant frequency?
A. Its reactance increases
B. Harmonics are generated
C. It becomes capacitive
D. Catastrophic failure is likely

An inductor consists of turns of insulated wire, and thus there is capacitance between these windings, Once a certain, self resonant frequency is exceeded, the capacitive effect becomes the primary factor, answer C.

What is the primary purpose of a screen grid in a vacuum tube?
A. To reduce grid-to-plate capacitance
B. To increase efficiency
C. To increase the control grid resistance
D. To decrease plate resistance

Valves with more than three electrodes, such as the tetrode and pentode (4 and 5 electrodes) have screen grids. The screen, often connected to the cathode, reduces the (control) grid to plate capacitance, answer A.

Why is the polarity of applied voltages important for polarized capacitors?
A. Incorrect polarity can cause the capacitor to short-circuit
B. Reverse voltages can destroy the dielectric layer of an electrolytic capacitor
C. The capacitor could overheat and explode
D. All of these choices are correct

Reverse voltage on a polarised electrolytic or tantalum capacitors, along with "super and "ultra" caps is bad news. Short circuits; destruction of the dielectric layer; and build-up of heat, resulting in the electrolyte becoming steam and either the top rupturing, or the capacitor body launching itself across the room, leaving just the wires behind are all possibilities, so answer D.

Which of the following is an advantage of ceramic capacitors as compared to other types of capacitors?
A. Tight tolerance
B. High stability
C. High capacitance for given volume
D. Comparatively low cost

These are affordable capacitors when a lower value devices is needed, and are suitable for use in some RF circuits, answer D.

You usually get several for a dollar. High performance silvered mica units, capable of handling high RF currents, are much more costly (a few dollars each), and not available in places like Jaycar, but rather from RS or Element 14, or from RF part specialist.

On to: Components 2 - Integrated Circuits, Displays & Connectors

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

Written by Julian Sortland, VK2YJS & AG6LE, April 2022.

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