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Amateur Radio Info & Exams - Electrical Units, Conductors & Insulators, AC & DC

Volts, Amps & Watts

My other pages have dealt with these, so a refresher:

Voltage, or Electromotive Force (EMF) is sometimes called electrical pressure, as it is what drives current through a circuit, overcoming resistance. It is measured in volts (v).

Current is the flow of electrical energy, measured in Amperes, or Amps (A). An Amp is the transfer of one coulomb of charge per second.

Resistance is in Ohms (Ω). Different metals have different resistances, and reducing the cross-section, or increasing the length of a wire increases the resistance. Likewise, metal films, carbon films, and carbon-ceramic pellets have various resistances. Resistance acts equally on DC and all frequencies of AC, including radio frequencies.

Power is the rate at which work is done, or energy expended, and it is expressed in Watts. Electrically, this is the multiple of voltage and current. It is also one joule per second.

Watts can also be use to express the power a Tour de France cyclist is using while climbing a mountain (say 400 watts), or the thermal output of a nuclear reactor from 10 MW for a research unit like HiFAR at Lucas Heights, to well over a gigawatt for a power reactor.

Fun thought on Energy and Power: If you have an economy car, and your friend has some ridiculous V8, and both have 50 litres of the same fuel in the tank, both contain the same ENERGY. However, one can convert the chemical energy to noise, oops, kinetic energy much faster than the other. This rate of conversion of energy is called POWER.

Supply voltage

Many devices are designed to operate on a tight range of voltages, such as a mobile radio designed for 12 to 14 volts. Some ICs (integrated circuits), especially "TTL" IC, a form of logic, require a close to 5 volts DC, as tight at 4.75 to 5.25 volts. Others, such as CMOS logic can operate between 3 to 18 volts, some down to 1.2 volts. Returning to mobile radios, as well as a car battery, these can be operated from a mains power supply, designed to put out around 13.8 volts. Suppose a radio's manual says it needs 22 amps, there is nothing wrong with a supply capable of a greater current, such as 30 or 40 amps. This can be used to supply various accessories too.

Many devices are designed to operate on a tight range of voltages, such as a mobile radio designed for 12 to 14 volts. Some ICs (integrated circuits), especially "TTL" IC, a form of logic, require a close to 5 volts DC, as tight at 4.75 to 5.25 volts. Others, such as CMOS logic can operate between 3 to 18 volts, some down to 1.2 volts. Returning to mobile radios, as well as a car battery, these can be operated from a mains power supply, designed to put out around 13.8 volts. Suppose a radio's manual says it needed 22 amps, there is nothing wrong with a supply capable of a greater current, such as 30 or 40 amps. This can be used to supply various accessories too.


Aussie readers should be familiar with most of these SI (metric) multipliers, but for those who aren't, relevant ones are:

GGigax 1 000 000 000
MMegax 1 000 000
kkilox 1 000
mmilli÷ 1 000
μmicro÷ 1 000 000
nnano÷ 1 000 000 000
ppico÷ 1 000 000 000 000
ffemto÷ 1 000 000 000 000 000

"kilo" gives us kilohertz, kilohms, kilograms, and water sold in kilolitres by utilities in metric countries, each one thousand of the base units. The kilovolt is 1000 volts, and a voltage used in valve transmitters.

"Mega" ia mostly used in megahertz and megohms. Megagrams, while logical, are replaced by the tonne, 1000 kg.

The amount of active ingredient in a tablet is expressed in milligrams or micrograms; although two 500 mg paracetamol / acetaminophen tablets make a 1 gram dose.

The milliamp features below, as 1/1000 of an Amp. US beverage containers often use ML, meaning Megalitres, roughly the capacity of a municipal swimming pool. Dr Pepper gets it at least partly right, using mL, although ml is ideal.

Rather than the Greek mu symbol, older publications may use mm, such as mmF meaning milli-mill-Farad. uF is also used in systems which can't handle μ.

In the regulations, called "Part 97", kilometres are used for distances away from borders and sites where various restrictions on transmissions apply. Both "km" and "kilometers" are used. On this paper, 50 km is the boundary between regulating a station as an earth station (on aircraft, balloons, small rockets), and as a space station, aboard the ISS or a satellite. This is 50,000 metres.

The following are traditional metric, but not SI:

hhectox 100
dadecax 10
ddeci÷ 10
ccenti÷ 100

A centimetre (or centimeter) is 100th of a metre, so bands like 70 cm or 23 cm have a wavelength of around 0.7 or 0.23 metres. In Europe centilitres (cl) is used for alcoholic drinks, and decilitres for small milk containers. Hectopascals are interchangeable with millibars.

Conductors & Insulators

For electrons to flow easily through a material it must have a certain atomic structures. These are found in metals, such as Copper, Aluminium, Silver, Gold, all solid at room temperature; and Mercury (quicksilver, from Old English cwicseolfor meaning "living silver"), liquid at room temperature. (This is a "heavy metal" which causes brain damage if the vapour in inhaled, but safe in very small quantities as a part of preservative compounds in pharmaceuticals). These are all called conductors. Some metals and alloys are poorer conductors, and can be formed into resistors, such as "Nichrome", a nickel and chrome alloy. Note that they still pass significant currents, but get hot when doing so, useful for toasting your bread, or heating water.

For electrons to flow easily through a material it must have a certain atomic structures. These are found in metals, such as Copper, Aluminium, Silver, Gold, all solid at room temperature; and Mercury (quicksilver, from Old English cwicseolfor meaning "living silver"), liquid at room temperature. (This is a "heavy metal" which causes brain damage if the vapour in inhaled, but safe in very small quantities as a part of preservative compounds in pharmaceuticals). These are all called conductors. Some metals and alloys are poorer conductors, and can be formed into resistors, such as "Nichrome", a nickel and chrome alloy. Note that they still pass significant currents, but get hot when doing so, useful for toasting your bread, or heating water.

Lead and Tin (PB and Sn) are quite good conductors, and are used to make solder. As lead is toxic most newer solders are mostly, even all, tin.

Materials which are the poorest conductors are called insulators. Great examples are glass and glazed ceramic material such as porcelain are used in high voltage power distribution systems. Most plastics, and most rubbers are fine at 240 volts, but note that rubber can "perish" and crumble, making old power leads use in valve radios, clothes irons, etc dangerous nowadays, unless modern wiring in fitted. Silicone rubber is great, and tolerates high temperatures. XLPE is a very good plastic insulator. Dried, and ideally lacquered wood, dry air, dry nitrogen, etc are also insulators.

Conductors inside pipes containing Sulphur Hexafluoride (SF₆) are used high-voltage switching stations, but this is a potent greenhouse gas, and should only be used in sealed systems. Metal oxides, such as aluminium oxide can be effective insulators, with this used in Mineral Insulated Metal Sheathed (MIMS) cables which can withstand very high temperatures. Glass-reinforced epoxy laminate, used in fibreglass printed circuit boards, and synthetic resin bonded paper, used in "phenolic" or "Bakelite" printed circuit boards, mica, PTFE (Teflon), even dry paper are other examples, as is mineral oil. If an excessive voltage is applied to any insulator it can suffer "breakdown", and conduct. The other PCB, Polychlorinated biphenyl, an oil-like liquid is also an excellent insulator, with very good thermal conduction characteristics, so was used in industrial capacitors and pole transformers. It is however carcinogenic, and toxic, so use has been discontinued.

Some forms of carbon can be formed into solids and films with known resistance, and are used to make low cost resistors. Metal films are also used, as are fine Nichrome wires wrapped onto formers. Graphite is a good conductor, nanotubes and graphine excellent ones, but diamond is the best insulator known.

Semiconductor materials include Silicon, Germanium, and Gallium-Arsenide. These can be influenced to conduct or not conduct by various means.

DC, AC, & RF


When you turn on a flashlight (a torch is a stick with fabric soaked in something flammable at one end, and set alight), a current flows from the positive terminal of the cell / battery, through a filament lamp, or through a light emitting diode (LED) and back to the negative terminal, continuing until you switch it off, or the chemical energy is depleted (the battery is "flat").

Note that the electrons actually flow from the negative to positive, but you don't need this for the Technician test, but it explains how electron tubes / thermionic valves work.

This is called Direct Current, or DC. Note however if you monitor the current at the positive terminal of a 12 volt car battery, you will notice current leaving to power your radio, etc while operating with the engine off, and to start the car, but once the engine has started, coming from the alternator to the battery to charge it. However, the voltage on the terminal will always be positive.


Rotating generators, where relative motion between conductors and magnetic fields is caused by energy from water falling, steam acting on a turbine, or engine, produce a sine-wave shaped voltage and current. Usually the current is extracted using slip rings, which result in the current changing direction many times per second as one side of the winding passes North and South magnetic fields. This AC can be at the voltage we wish to use, in a small emergency or camping unit, or at a fairly high voltage, which is then transformed up to an even higher voltage for transmission, then stepped down a few times to be consumed in your home, office, etc. This is the big advantage of AC, that it can be easily stepped up or down using a transformer.

Rectification can be achieved using a simple diode bridge to make rough DC, which can be filtered using a capacitor.

In a modern car the "alternator" includes a diode bridge to make the DC to charge the battery, and power fuel pumps, injection, ignition (in gasoline and LPG engines), lighting, etc. In old cars the "dyno" has a split armature which means the side of the winding passing, say the N pole is always connected to the positive terminal. Thus rectification is achieved mechanically. These are however less efficient that the modern system. Automotive alternators are actually three phase, so there is a lower ripple, as one of the phases is always supplying current, unlike in a dyno, where the voltage falls to zero twice each revolution.

The US mains frequency is 60 Hertz, meaning 60 cycles of zero to positive, back through zero becoming negative, then back to zero, every second. Old documents use the term "cycles" or "cycles per second" (c.p.s.). Australia uses 50 Hz. Aircraft and ship-board radar use 400 Hz. Poorly written notes say there are 60 changes of direction per second, but there is actually twice this. When DC us rectified using a single diode, a 60 Hz hum may be caused if the capacitor is faulty, but 120 Hz if it is full-wave rectified (50 or 100 Hz Down-under or in Europe).

Not in the exam, converting DC to AC is a more complex affair, requiring an oscillator, switching transistors, and a transformer, forming a device called an "inverter". The WWII method for valve (tube) aircraft radios, etc, was to use a DC motor to drive a generator, although this could be DC, as that is what the valves required.

When an audio signal is taken from a microphone, or generated in an electric device, it forms an AC signal of varying frequency and level (amplitude). In broadcast audio or hi-fi systems the exact range the system handles varies a little, but the range is roughly 20 Hz to 20,000 Hz (20 kHz), maybe a little more. This is the range of hearing in a younger person who has not listened to loud music excessively, but age and industrial noise damages the sensitive receptors for higher tones. The speaking voice covers around 300 Hz to 3.4 kHz, certainly this is the range needed for understanding a message. Thus telephones and radio communications systems concentrate on this band, called Voice Frequency (VF).


Radio frequencies overlap with the highest audio ones, starting at around 10 kHz for longwave or very low frequency (VLF) signals, use as time signals. The upper frequency is a few hundred gigahertz.

While sounds needs a medium such as air, but radio signals can travel through space, air, non-metallic wall materials (with varying loss), and glass, although this depending on metallisation, such as in some train windows, and frequency.

Radio Frequency is also expressed in Hertz, but more usually kilohertz (kHz), megahertz (MHz), or gigahertz (GHz) are used. Often instead of using 3.6 MHz the frequency is expressed as 3600 kHz, and as you can see, as the multiplier changes, a factor such as 1000 is applied. The same is used converting between 2.45 GHz and 2450 MHz.

Comment on number format

Note that these questions and maths use the English / American / Australian tradition of using a dot . as the decimal point, and a comma , as a thousands indicator. Some Europeans swap these. Northern Europeans also used the Obelus we use as a division sign, ÷ as a minus sign, surviving in Norwegian retail store-front advertising, as "÷33%" for a price reduction of 33%. I have mostly used / for division, as it can be most easily typed.


Capacitors store energy in the dielectric (insulating material) between the plates. This is different to a battery which stores energy chemically. Capacitance is measured in Farads (F) which is a very large unit. Most capacitors range from picofarads in radio frequency circuits, up to thousands of microfarads in power supplies. Thus, pF, nF, μF are common, and going up to fractional or whole Farads for specialised "supercapacitors" used for backing up memory in some microprocessor systems (0.47F, 10F, etc) and "ultracapacitors". mF is not used often, with regular electrolytics marked as, say 22,000μF, or "super-caps" as 0.47F instead. While it is usual to buy capacitors, they can be made from materials such as metal plates or foils, and picture-frame glass (it's thinner) or plastic sheet.

Larger plate areas increases capacitance, but greater spacing significantly decreases it, hence the comment on the thinner glass.

Capacitance occurs naturally, and even 2 wires side by side have capacitance. Often this is only an issue at audio and RF frequencies, but at home I put a 5 watt compact fluorescent lamp in the hall, and the capacitance of nearly 20 metres of parallel wire (held in a cable) for the 2-way stitching arrangement caused enough current to flow, via the bridge rectifier, into the capacitor in the lamp that it would periodically attempt to start up, causing it to flash about every 5 seconds.

Off the exam, but very high capacity capacitors are now being used in new applications. One is in the Newcastle Light Rail (tram) in Australia. Instead of the usual overhead wiring, at each stop the tram raises a pick-up to a heavy bar, and charges for about 30 seconds. This provides enough energy to travel to the next stop. There are also batteries for on-board systems, with enough energy to crawl back to the depot, should the whole charging system turn to custard. Read about CAF's Acumulador de Carga RĂ¡pida.


An inductor is a coil of wire either insulated (often by enamel) or by spacers. It is measured in Henries, with 1 henry (H) being quite a large quantity. Most components are millihenries (mH) or microhenries (μH). They can be bought, or wound by hand.


In the manufacture of all kinds of electronic components there is a variation from the intended value. Old school carbon composition resistors can be up to 20% above or below the marked value, although modern versions, used in RF circuits (they are less inductive) can be 5%. Carbon film are typically 5%. Metal film resistors are usually 1%, at little extra cost, although 0.1% ones can be up to a few dollars each. There are standard series, such as E6, with 6 values for each "decade", these being 100, 150, 220, 330, 470, 680, repeating from 1000 to 6k8; this used for wide tolerance devices, E12 and E24 are often available from retailers, with E48, E96, and E192 available at specialist distributors and online. You can read more here: Resistor Values

Decibels - dB

Ratios of power can be very large, from around a million watts emitted by a transmitter in Russia, to well under a trillionth of a watt reaching your radio's antenna connector. Talking about 1/1000000000000000000 of the power is pretty awkward, and even 10E-18 is messy, but if there was a logarithmic ratio, then you could just write -180 dB. It is also easy to factor in cable losses, transmitter antenna gain, path loss, receiver antenna gain, pre-amp gain, cable loss, etc. While the maths involves log10, and might appear complex, the whole thing uses some simple ratios.

A Bel is a 10 times ratio, but normally a decibel is used. A 10 times change is 10 dB. An increase is positive, a decrease negative. Other easy ratios are 3 dB, being a doubling in power, -3 dB being a halving power. +6 dB or -6 dB is a ratio of 4 times. +4 dB can be calculated as x10 then ÷4, so 2.5 times the original signal.

When an amplifier, either a receiver amplifier (often called a pre-amp), or a power amplifier (often called a "linear"), the energy it puts out must come from a power supply of some sort.

When an antenna has gain, the gain comes by either directing the power in a particular direction, or selecting the direction in which it is received from. Yagi and dish antennas are examples. A vertical antenna can have gain by reducing the radiation angle so energy is sent towards the horizon, rather than allowed to spread upwards, causing a greater portion to be lost into space. Going from a quarter-wave antenna to a five-eighth wavelength one does this, with the downside of having to avoid low-flying car-park entrances.

A level can also be specified in dB relative to a fixed unit, such as dBW, relative to 1 watt, and example being the NZ Amateur Regulations, where the limit on many bands is 30 dBW, meaning 30 dB above one watt, or 1,000 watts (1Kw). It's not only rugby they beat us at... Other relevant examples are dBm, that is, relative to 1 milliwatt, and dBμV, relative to 1 microvolt. It is also used in Sound Pressure Level, relative to 20 micropascals, around the threshold of hearing.

Signals reflected from antennas are related to SWR (standing wave ratio), where a low ratio (close to 1:1, rather than, say 3:1 is good, or "return loss", where more is better (100 watts "up the stick", 2 w back is not bad, a 17 dB return loss, or an SWR of 1.3:1. If you turn radio into a job, it is when working with high power broadcast systems that you do need a much better figure.

⅝ Antenna

An antenna with a length of 5/8, or 0.625 of a wavelength has modest gain over one of 1/4, or 0.25 wavelength. It is nowhere near the 10dB one of the spoilers suggests. For 2 metres (147 MHz) it has a length of somewhat over 1.2 metres. Off this exam, it has a small coil at the base of the whip to cancel its capacitance.

Relevant Questions

These are the actual questions relating to the information above.

Remember, if you get stuck on a question, work through the answers and exclude the wrong ones: Volts, voltage; Watts, that is power, because my car has 100 kilowatts; current is flow, and plugs and fuses are specified in Amps or Amperes; Ohms, they are resistance / impedance, because the sales person at Radio Shack said I needed 4 ohm (4 Ω) speakers for my car. Unlike school, there is no time limit on the test. Plus, if you are really stumped, come go on, and come back to that question later.

Electrical current is measured in which of the following units?
A. Volts
B. Watts
C. Ohms
D. Amperes

Current is in Amperes, answer D. It was named for André-Marie Ampère, a French physicist. "Amps" is plural of the short name.

Electrical power is measured in which of the following units?
A. Volts
B. Watts
C. Ohms
D. Amperes

What's the unit of Power? Watts! Answer B. This is named for the Scottish inventor, James Watt.

What is the name for the flow of electrons in an electric circuit?
A. Voltage
B. Resistance
C. Capacitance
D. Current

This is current, answer D.

What do you have to be careful of if swimming in a river? The flow of water, or current!

What are the units of electrical resistance?
A. Siemens
B. Mhos
C. Ohms
D. Coulombs

This is the ohm, named for the German Georg Ohm. Answer C.

What is the electrical term for the force that causes electron flow?
A. Voltage
B. Ampere-hours
C. Capacitance
D. Inductance

Voltage is considered "electrical pressure", and it is what drives, or forces, current through a circuit, answer A.

Volts are named for the Italian Alessandro Volta, who invented an early battery, the voltaic pile, made from zinc and copper discs, and cardboard soaked in sulphuric acid or brine.

What is the unit of frequency?
A. Hertz
B. Henry
C. Farad
D. Tesla

This is Hertz, answer A; be in the 50 or 60 Hz of wall power, or the 27 MHz figure which defines HF CB in Australia.

It is named for Heinrich Hertz, the German who did the hands-on experiments on radio waves, proving Maxwell's theories.

Why are metals generally good conductors of electricity? A. They have relatively high density B. They have many free electrons C. They have many free protons D. All these choices are correct

Metals have many free electrons, answewr B.

Which of the following is a good electrical insulator?
A. Copper
B. Glass
C. Aluminum
D. Mercury

Glass is a great insulator, so answer B. Glass insulators from old telegraph, telephone and railway signal wires have become collector's items and can be seen in antique and junk shops.

Which of the following describes alternating current?
A. Current that alternates between a positive direction and zero
B. Current that alternates between a negative direction and zero
C. Current that alternates between positive and negative directions
D. All these answers are correct

Alternating implies a reversal on a regular basis, and this means a full reversal, with positive AND negative periods, answer C.

The other two options describe unfiltered DC, which appears beyond a rectifier when there are no filter capacitors.

This link will take you down the Rectifier Rabbit Hole: Wikipedia - Rectifier

Which term describes the rate at which electrical energy is used?
A. Resistance
B. Current
C. Power
D. Voltage

The key words are rate and energy, and the rate of energy use is Power, answer C. A watt is one joule per second, a joule being the unit of energy, so the watt a rate of use of energy.

The kilowatt is the true metric cousin of the Horse Power. However, most of Europe advertises cars in a soft metric unit called whatever the words for "horse" and "power" are, even the Brits use the German term, because the unit is smaller, and thus the number is bigger.

What type of current flow is opposed by resistance?
A. Direct current
B. Alternating current
C. RF current
D. All these choices are correct

Resistance reduces the flow of all currents, answer D.

What describes the number of times per second that an alternating current makes a complete cycle?
A. Pulse rate
B. Speed
C. Wavelength
D. Frequency

The number of cycles is the frequency, answer D, frequency.

A cycle starts (say) at zero, as the voltage climbs to a positive peak, before it diminishes, passing through zero, reaching a negative peak, then climbing back to zero. Pulse rate usually relates to something like the signal from a sensor on a modern car's driveshaft going into an electronic speedo circuit. Speed is the street name for a dangerous drug, hence the "speed kills" signs besides roads. Velocity is however a factor in calculating wavelength. Wavelength is the inverse of frequency, decreasing with increase in frequency.

Those who studied calculus will know about differentiation and integration of waveforms such as sine waves.

How many milliamperes is 1.5 amperes?
A. 15 milliamperes
B. 150 milliamperes
C. 1500 milliamperes
D. 15,000 milliamperes

SI (formal metric) uses multiples of 1000, with "milli" meaning a 1/1000 part. Thus 1.5 amps in 1500 milliamps. Answer C!

Which is equal to 1,500,000 hertz?
A. 1500 kHz
B. 1500 MHz
C. 15 GHz
D. 150 kHz

This is a frequency in the medium wave broadcast band, 1500 thousand Hz, or 1500 kHz, answer A.

Which is equal to one kilovolt?
A. One one-thousandth of a volt
B. One hundred volts
C. One thousand volts
D. One million volts

Kilo is 1000, as in a kilogram being 1000 grams, so a kilovolt is 1000 volts, answer C.

Which is equal to one microvolt?
A. One one-millionth of a volt
B. One million volts
C. One thousand kilovolts
D. One one-thousandth of a volt

Micro is a millionth, so 1 μV is one one-millionth of a volt, Answer A.

1 μV what a fairly weak radio signal might present to the antenna input of your radio.

Which of the following is equivalent to 500 milliwatts?
A. 0.02 watts
B. 0.5 watts
C. 5 watts
D. 50 watts

Half a watt, is also 0.5 watts, answer B.

This might be the power output of a hand-held radio on the low power setting, or the power out of a simple home-built "QRP" transmitter.

If an ammeter calibrated in amperes is used to measure a 3000-milliampere current, what reading would it show?
A. 0.003 amperes
B. 0.3 amperes
C. 3,000,000 amperes
D. 3 amperes

There are thousand milli-units in a unit, so 3000 mA is 3 Amps, so answer D.

Which is equal to 3.525 MHz?
A. 0.003525 kHz
B. 35.25 kHz
C. 3525 kHz
D. 3,525,000 kHz

This frequency is an HF radio frequency, in the 80 metre band. It is also 3525 kHz, answer C.

In the 80 metre band either form is quite common. Beware the k in kHz in the last option, as the correct value is 3 525 000 HERTZ, NOT 3 525 000 kHz, a microwave frequency.

Which is equal to 1,000,000 picofarads?
A. 0.001 microfarads
B. 1 microfarad
C. 1000 microfarads
D. 1,000,000,000 microfarads

A picofarad is one trillionth of a farad, meaning one millionth part of a millionth part. A million trillionths is a one millionth, as you cancel out 6 of the zeros. The answer is B, 1 μF.

In low value capacitors, such as ceramics and polyester, one numbering scheme is to mark in picofarads such as: 105, meaning 10, followed by 5 more zeros, or a million pF, or 1 μF.

Which decibel value most closely represents a power increase from 5 watts to 10 watts?
A. 2 dB
B. 3 dB
C. 5 dB
D. 10 dB

5 to 10 watts is doubling power, and that is +3 dB, answer B.

Which decibel value most closely represents a power decrease from 12 watts to 3 watts?
A. -1 dB
B. -3 dB
C. -6 dB
D. -9 dB

Halve the power, 12 watts to get 6 w, and halve it again, 3w. Halving is -3 dB, so do it twice, and it is -6 dB, answer C.

Which decibel value represents a power increase from 20 watts to 200 watts?
A. 10 dB
B. 12 dB
C. 18 dB
D. 28 dB

Ramping the power up by 10 times is one Bel, written as 10 decibels or 10 dB, answer A.

Which is equal to 28400 kHz?
A. 28.400 MHz
B. 2.800 MHz
C. 284.00 MHz
D. 28.400 kHz

To convert from kHz to MHz, divide by 1000, meaning move the decimal three places to the left. Thus we get 28.400 MHz, answer A.

As the answer order can be changed in the real exam, watch out for the kHz option, in the ultrasonic range!

28.400 MHz is a frequency in the 10 metre band, which Technicians and Novices may use, at a power of up to 200 watts PEP.

Which is equal to 2425 MHz?
A. 0.002425 GHZ
B. 24.25 GHz
C. 2.425 GHz
D. 2425 GHz

Similar to the previous question, divide by 1000, by moving the decimal left three places (the decimal is at the right of the units position), so getting 2.425 GHz, answer C.

This is a 13 cm frequency, and also in the Industrial, Scientific, and Medical (ISM) band, used for things like microwave ovens, WiFI, Bluetooth, or retro-fitting a reversing camera to a vehicle, or the probably distracting practice of monitoring the inside of a horse-box.

What is the ability to store energy in an electric field called?
A. Inductance
B. Resistance
C. Tolerance
D. Capacitance

The electric field between the plates of a capacitor stores energy, thus the answer is Capacitance, answer D.

Banks of large, high voltage capacitors can store enough energy to do a range of often destructive things, such as discharge thousands of amps through a very heavy coil of cable, of just a few turns, and crush a beverage can with the magnetic effect. More usually they are used in camera flashes, or to smooth ripple in power supplies. Another use is to maintain power to a memory chip, to retain settings in a radio, etc.

What is the unit of capacitance?
A. The farad
B. The ohm
C. The volt
D. The henry

The unit is the Farad, answer A. It is named for Michael Faraday, an English scientist.

What describes the ability to store energy in a magnetic field?
A. Admittance
B. Capacitance
C. Resistance
D. Inductance

Inductors use magnetic fields, so answer D. (Admittance is how easily a circuit allows current to flow, and is the inverse of inductance. Like Conductance (inverse of resistance), it is measured in Siemens, once called mhos.)

You might think not much energy is stored in this way, but it can actually be significant. Further examples of inductors include relay coils, and the windings of transformers. Many circuits with a transistor switching current for a relay coil (with the coil in place of the lamp in Figure T-1) include a diode backwards across the coil to short the current generated when the current through the coil is turned off, and the magnetic field collapses, this causing relative motion between the wires of the coil, and this collapsing magnetic field. Without the low resistance path via the diode, the energy could cause a high-voltage pulse which may damage the transistor. Modern "automotive relay driver" transistors and FETs may be designed not to need the diode.

In another case, an instructor at Telecom mentioned that he had been testing the DC resistance of a winding of a large transformer (bigger than him), and when he removed the test probes the energy from a single 1.5 volt battery stored over the several minutes it took for the reading to stabilise (due to the inductance resisting the initial flow of current from the meter), that energy became a powerful high-voltage electrical pulse, enough to knock him off his feet! Collapsing fields are also used in Tesla Coils and automotive ignition, where the opening of the points cutting primary current generates a high voltage pulse in the secondary, generating a spark.

What is the unit of inductance?
A. The coulomb
B. The farad
C. The henry
D. The ohm

Inductance is measured using the Henry. The Answer is C.

I suppose you could picture a bloke called Henry winding inductors: Many radio related kits supply you with a core or former of some sort, and a length of enamel insulated wire to wind the inductor(s) with. It is named for Joseph Henry, an American scientist who co-discovered electromagnetism.

What is the unit of impedance?
A. The volt
B. The ampere
C. The coulomb
D. The ohm

This is the ohm, answer D.

The Ohm a unit for resistance, for reactance, and for the vector sum of these, impedance. In most cases, a vertical antenna mounted on a vehicle, etc, should have an impedance of 50 ohm.

What does the abbreviation "RF" mean?
A. Radio frequency signals of all types
B. The resonant frequency of a tuned circuit
C. The real frequency transmitted as opposed to the apparent frequency
D. Reflective force in antenna transmission lines

RF stands for Radio Frequency, answer A.

What is antenna gain?
A. The additional power that is added to the transmitter power
B. The additional power that is lost in the antenna when transmitting on a higher frequency
C. The increase in signal strength in a specified direction when compared to a reference antenna
D. The increase in impedance on receive or transmit compared to a reference antenna

Antenna gain is the measure of how much an antenna directs signals in a particular direction. For a yagi antenna this is often in a geographic direction, but can be towards a man-made satellite, or the moon. This is compared to a reference antenna, either a dipole, or an imaginary "isotropic radiator", which radiates in all directions equally, similarly to a light globe. These are in dBd or dBi, respectively. There is 2.15 dB between the dBd and dBi figure, so some marketers use dBi to make their antenna look better to the uninformed. The answer is C. Antennas are not powered, so are not capable of adding power, just directing it. Impedance is not directly linked to gain, although inefficient electrically short vertical antennas, such as 9 ft steel whips when used below 27 MHz require some sort of impedance matching system, as they are far from 50 ohms.

What is an advantage of a 5/8 wavelength whip antenna for VHF or UHF mobile service?
A. It has more gain than a 1/4-wavelength antenna
B. It radiates at a very high angle
C. It eliminates distortion caused by reflected signals
D. It has 10 times the power gain of a 1/4 wavelength whip

⅝ antennas have a lower angle of radiation than a quarter-wave, which often improves coverage, or the range from which you can access a repeater. In other words, it has more gain than a ¼ antenna, answer A.

Even if a repeater is in a high site, generally the angle to it is still fairly low (unless you are, say down Galston Gorge). A ⅝ can reduce "picket fencing", an effect caused by driving through an area where there are peaks and nulls in the signal due to reflections, but this in not a complete fix.

On to: Frequency, Wavelength and Bands

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

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

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