Receivers, transmitters, transceivers, and transverters

In the early days of radio, radio amateurs used separate receivers and transmitter units. Nowadays, however, most use radios that combine function both as the transmitter and receiver. These unit are called transceivers.

T7A02
What is a transceiver?
A. A device that combines a receiver and transmitter
B. A device for matching feed line impedance to 50 ohms
C. A device for automatically sending and decoding Morse code
D. A device for converting receiver and transmitter frequencies to another band

Often, HF transceivers are used with devices called transverters that convert the signals from their HF transceiver to the VHF, UHF, and even microwave bands. Transverters take the output of an HF transceiver, normally set to the 10 m (28 MHz) band and output a VHF, UHF, or microwave signal. Conversely, they receive a VHF, UHF, or microwave signal and output a signal in the 10 m band that is demodulated by the HF transceiver.

T7A06
What device converts the RF input and output of a transceiver to another band?
A. High pass filter
B. Low-pass filter
C. Transverter
D. Phase converter

Many, if not most, new amateurs buy a handheld transceiver, called an “HT,” as their first transceiver. One disadvantage of using a handheld transceiver is that the maximum output power is generally only 5 W, and because of this, they have limited range. To get around this limitation, you can use an RF amplifier to boost the power.

T7A10
What device increases the transmitted output power from a transceiver?
A. A voltage divider
B. An RF power amplifier
C. An impedance network
D. All these choices are correct

T7A09
What is the function of the SSB/CW-FM switch on a VHF power amplifier?
A. Change the mode of the transmitted signal
B. Set the amplifier for proper operation in the selected mode
C. Change the frequency range of the amplifier to operate in the proper segment of the band
D. Reduce the received signal noise

When talking about a transceiver’s specifications, we still refer to its receiver and transmitter. The two most important receiver specifications are sensitivity and selectivity.

T7A01
Which term describes the ability of a receiver to detect the presence of a signal?
A. Linearity
B. Sensitivity
C. Selectivity
D. Total Harmonic Distortion

T7A04
Which term describes the ability of a receiver to discriminate between multiple signals?
A. Discrimination ratio
B. Sensitivity
C. Selectivity
D. Harmonic distortion

To improve the sensitivity of a receiver, you can use an RF preamplifier. An RF preamplifier amplifies signals that you want to receive.

T7A11
Where is an RF preamplifier installed?
A. Between the antenna and receiver
B. At the output of the transmitter power amplifier
C. Between the transmitter and the antenna tuner
D. At the output of the receiver audio amplifier

Many HF transceivers have some version of a superheterodyne receiver. A superheterodyne receiver converts an incoming radio signal to an intermediate frequency, or IF. The circuit that does this is the mixer.

T7A03
Which of the following is used to convert a signal from one frequency to another?
A. Phase splitter
B. Mixer
C. Inverter
D. Amplifier

When transmitting or receiving, we want to generate an RF signal with a specific frequency. To do that, we use an oscillator.

T7A05
What is the name of a circuit that generates a signal at a specific frequency?
A. Reactance modulator
B. Phase modulator
C. Low-pass filter
D. Oscillator

To transmit a voice or data signal, we have to combine an audio frequency signal from the microphone with the RF carrier signal generated by the transmitter. This is done with a circuit called a modulator, and the process of combinging speech with an RF carrier signal is called modulation.

T7A08
Which of the following describes combining speech with an RF carrier signal?
A. Impedance matching
B. Oscillation
C. Modulation
D. Low-pass filtering

Symptoms, causes, and cures of common transmitter and receiver problems

Since Murphy’s Law—the law that states if anything can go wrong, it will—applies to amateur radio as much as it does to any other pursuit, at some point you will have to deal with problems. These may include overload, distortion, feedback, and radio frequency interference, or RFI.

Let’s first consider radio frequency interference.

T7B03
Which of the following can cause radio frequency interference?
A. Fundamental overload
B. Harmonics
C. Spurious emissions
D. All these choices are correct

Any of these could cause interference to a TV set or radio or even computer speakers, and you will want to take steps to find and eliminate that interference. The first thing that you should do if your neighbor complains about interference is to make sure that your station is functioning properly by making sure that your transmissions do not cause interference to your radios or televisions.

T7B06
Which of the following actions should you take if a neighbor tells you that your station’s transmissions are interfering with their radio or TV reception?
A. Make sure that your station is functioning properly and that it does not cause interference to your own radio or television when it is tuned to the same channel
B. Immediately turn off your transmitter and contact the nearest FCC office for assistance
C. Install a harmonic doubler on the output of your transmitter and tune it until the interference is eliminated
D. All these choices are correct

While it’s not very likely that your amateur radio station will interfere with a neighbor’s cable TV service, it can sometimes occur. If you are interfering with a neighbor’s cable TV service, first check the coax connectors.

T7B09
What should be the first step to resolve non-fiber optic cable TV interference caused by your amateur radio transmission?
A. Add a low-pass filter to the TV antenna input
B. Add a high-pass filter to the TV antenna input
C. Add a preamplifier to the TV antenna input
D. Be sure all TV feed line coaxial connectors are installed properly

Your amateur radio station may interfere with a nearby radio receiver if your signal is so strong that the receiver cannot reject the signal even though your signal is not on the frequency to which the receiver is tuned. This is called fundamental overload.

T7B02
What would cause a broadcast AM or FM radio to receive an amateur radio transmission unintentionally?
A. The receiver is unable to reject strong signals outside the AM or FM band
B. The microphone gain of the transmitter is turned up too high
C. The audio amplifier of the transmitter is overloaded
D. The deviation of an FM transmitter is set too low

To reduce or eliminate fundamental overload, you can install a filter at the radio or TV input to block the interfering signal.

T7B05
How can fundamental overload of a non-amateur radio or TV receiver by an amateur signal be reduced or eliminated?
A. Block the amateur signal with a filter at the antenna input of the affected receiver
B. Block the interfering signal with a filter on the amateur transmitter
C. Switch the transmitter from FM to SSB
D. Switch the transmitter to a narrow-band mode

The process can work the other way, too. When driving by the antenna of a high-power broadcast station you may notice that your VHF transceiver is picking up the broadcast station signal. This is often the result of overload.

T7B07
Which of the following can reduce overload of a VHF transceiver by a nearby commercial FM station?
A. Installing an RF preamplifier
B. Using double-shielded coaxial cable
C. Installing bypass capacitors on the microphone cable
D. Installing a band-reject filter

The band of frequencies that you want to reject is the band that includes the broadcast station frequency.

Interference works both ways. Your neighbors may have wireless devices that can interfere with your station. While they are responsible for eliminating the interference, chances are they don’t have the expertise necessary to find and eliminate the interference, so your best option is to try and work with them.

T7B08
What should you do if something in a neighbor’s home is causing harmful interference to your amateur station?
A. Work with your neighbor to identify the offending device
B. Politely inform your neighbor that FCC rules prohibit the use of devices that cause interference
C. Make sure your station meets the standards of good amateur practice
D. All these choices are correct

Perhaps the most common problem that amateur radio operators have is distorted or noisy audio when transmitting. There are many reasons for poor audio.

T7B10
What might be a problem if you receive a report that your audio signal through an FM repeater is distorted or unintelligible?
A. Your transmitter is slightly off frequency
B. Your batteries are running low
C. You are in a bad location
D. All these choices are correct

T7B11
What is a symptom of RF feedback in a transmitter or transceiver?
A. Excessive SWR at the antenna connection
B. The transmitter will not stay on the desired frequency
C. Reports of garbled, distorted, or unintelligible voice transmissions
D. Frequent blowing of power supply fuses

Sometimes, garbled or distorted audio when operating FM is the result of over-deviation.

T7B01
What can you do if you are told your FM handheld or mobile transceiver is over-deviating?
A. Talk louder into the microphone
B. Let the transceiver cool off
C. Change to a higher power level
D. Talk farther away from the microphone

Using basic test instruments and soldering

The most common test instrument in an amateur radio shack is the multimeter. Multimeters are called that because they combine the functions of a voltmeter, ohmmeter, and ammeter into a single instrument.

T7D07
Which of the following measurements are made using a multimeter?
A. Signal strength and noise
B. Impedance and reactance
C. Voltage and resistance
D. All these choices are correct

The voltmeter function of the multimeter is used to measure electromotive force, more commonly known as voltage. You measure the voltage across a component or circuit by connecting the leads in parallel with the component.

T7D01
Which instrument would you use to measure electric potential?
A. An ammeter
B. A voltmeter
C. A wavemeter
D. An ohmmeter

T7D02
How is a voltmeter connected to a component to measure applied voltage?
A. In series
B. In parallel
C. In quadrature
D. In phase

In order to avoid damaging the multimeter, make sure that it’s set to the voltage setting, not the resistance setting when you want to measure voltage.

T7D06
Which of the following can damage a multimeter?
A. Attempting to measure resistance using the voltage setting
B. Failing to connect one of the probes to ground
C. Attempting to measure voltage when using the resistance setting
D. Not allowing it to warm up properly

The ohmmeter function of a multimeter is used to measure resistance. The way an ohmmeter measures the resistance of a circuit is by supplying a known current to the circuit, measuring the voltage across the circuit, and then calculating the resistance using Ohm’s Law, R = V/I. Because we’re actually measuring voltage, we connect an ohmmeter in parallel with a component to measure its resistance.

T7D05
How is an ohmmeter connected to a component to measure its resistance?
A. In parallel
B. In series
C. In cascade
D. All these choices are correct

T7D11
Which of the following precautions should be taken when measuring in-circuit resistance with an ohmmeter?
A. Ensure that the applied voltages are correct
B. Ensure that the circuit is not powered
C. Ensure that the circuit is grounded
D. Ensure that the circuit is operating at the correct frequency

T7D10
What reading indicates that an ohmmeter is connected across a large, discharged capacitor?
A. Increasing resistance with time
B. Decreasing resistance with time
C. Steady full-scale reading
D. Alternating between open and short circuit

The ammeter function of a multimeter is used to measure current. You connect an ammeter in series with a circuit so that the current flowing through the circuit also flows through the ammeter.

T7D04
Which instrument is used to measure electric current?
A. An ohmmeter
B. An electrometer
C. A voltmeter
D. An ammeter

T7D03
When configured to measure current, how is a multimeter connected to a component?
A. In series
B. In parallel
C. In quadrature
D. In phase

In addition to knowing how to make electrical measurements, knowing how to solder is an essential skill for amateur radio operators.

T7D08
Which of the following types of solder should not be used for radio and electronic applications?
A. Acid-core solder
B. Lead-tin solder
C. Rosin-core solder
D. Tin-copper solder

T7D09
What is the characteristic appearance of a cold tin-lead solder joint?
A. Dark black spots
B. A bright or shiny surface
C. A rough or lumpy surface
D. Excessive solder

We call a poor solder joint a “cold” solder joint because it’s usually the result of not applying enough heat to the joint. When you don’t apply enough heat to a solder joint, the solder does not flow smoothly between the metal surfaces to be joined and often does not make a good connection.

Station setup

When setting up an amateur radio station, choosing the radio is the most important consideration, but you must also choose a wide range of accessories, such as power supplies and microphones. In addition, how you connect all these pieces of equipment together is important for your station to operate properly.

For example, a transceiver’s DC power cable should be made with short, heavy-gauge wires. The reason for this is that when transmitting, the transceiver draws a lot of current, and the resistance of the wires connecting the power supply to the transceiver will have a measurable voltage drop. If this voltage drop is too large, the transceiver will malfunction. Short, heavy-gauge wires have a lower resistance than long, thin wires, and therefore, a lower voltage drop.

T4A03
Why are short, heavy-gauge wires used for a transceiver’s DC power connection?
A. To minimize voltage drop when transmitting
B. To provide a good counterpoise for the antenna
C. To avoid RF interference
D. All these choices are correct

When choosing a power supply, check the voltage and current ratings of the supply and be sure to choose one capable of supplying the proper voltage and current to power your radio. Let’s look at an example.

T4A01
Which of the following is an appropriate power supply rating for a typical 50 watt output mobile FM transceiver?
A. 24.0 volts at 4 amperes
B. 13.8 volts at 4 amperes
C. 24.0 volts at 12 amperes
D. 13.8 volts at 12 amperes

There are two reasons why D is the correct answer. First, most mobile FM transceivers are designed to operate with a supply voltage between 11 V and 15 V. That means that the correct answer has to be either B or D. Second, B is incorrect because transceivers are 50% efficient at best, meaning that a 50 W output transceiver will need at least 100 W of power to operate correctly. A supply providing 13.8 V at 4 amperes is supplying only 55 W of power (P = E x I = 13.8 x 4 = 55.2 W), so this supply would be under-powered. That leaves D—13.8 volts at 12 amperes—as the correct answer.

A computer has become a common accessory in many amateur radio stations. Amateurs use them to operate digital modes, log contacts, and design circuits and antennas. I even use mine to Twitter while I’m on the air. When operating digital modes, such as FT8, you connect the transceiver’s receive audio, transmit audio, and transmitter keying to a computer. The transceiver audio output, such as the speaker connection, connects to the computer “line in.” Similarly, the transceiver audio input connects to the “line out” of the computer.

T4A06
What signals are used in a computer-radio interface for digital mode operation?
A. Receive and transmit mode, status, and location
B. Antenna and RF power
C. Receive audio, transmit audio, and transmitter keying
D. NMEA GPS location and DC power

T4A04
How are the transceiver audio input and output connected in a station configured to operate using FT8?
A. To a computer running a terminal program and connected to a terminal node controller unit
B. To the audio input and output of a computer running WSJT-X software
C. To an FT8 conversion unit, a keyboard, and a computer monitor
D. To a computer connected to the FT8converter.com website

T4A07
Which of the following connections is made between a computer and a transceiver to use computer software when operating digital modes?
A. Computer “line out” to transceiver push-to-talk
B. Computer “line in” to transceiver push-to-talk
C. Computer “line in” to transceiver speaker connector
D. Computer “line out” to transceiver speaker connector

Audio, microphone, and power supply cables in an amateur radio station sometimes pick up stray RF when you’re transmitting. At minimum, this RF can cause the audio to be distorted. At worst, it can cause a radio or accessory to malfunction. One way to cure this problem is by installing a ferrite choke on the shield of the microphone cable to block or “choke” any RF currents induced on the cable.

T7B04
Which of the following could you use to cure distorted audio caused by RF current on the shield of a microphone cable?
A. Band-pass filter
B. Low-pass filter
C. Preamplifier
D. Ferrite choke

Good grounding techniques can help you avoid interference problems. When grounding your equipment, you should connect the various pieces of equipment to a single point, keep leads short, and use a heavy conductor to connect to ground. We sometimes call this process bonding.

T4A08
Which of the following conductors is preferred for bonding at RF?
A. Copper braid removed from coaxial cable
B. Steel wire
C. Twisted-pair cable
D. Flat copper strap

If you plan to install a radio in your car and operate mobile, you have a different set of challenges. One is connecting the radio to the car’s power system. Some amateurs connect their radio with a cigarette lighter plug, but this plug is not designed for high currents. For permanent installations, you need to connect the negative power return to the 12 volt battery chassis ground.

T4A11
Where should the negative power return of a mobile transceiver be connected in a vehicle?
A. At the 12 volt battery chassis ground
B. At the antenna mount
C. To any metal part of the vehicle
D. Through the transceiver’s mounting bracket

The positive connection can be made at the battery or through an unused position of the vehicle’s fuse block.

You can also operate your equipment from a battery when operating portable or at home should the power be off. Of course, batteries have a finite life, and the more current you draw from the battery, the faster it will discharge. To determine how long you can operate using battery power, divide the battery ampere-hour rating by the average current draw of the equipment. For example, if you have a 10 amp-hour battery, and the average current draw is 1 amp, then you can operate for approximately 10 hours: operating time = 10 amp-hours / 1 amp = 10 hours.

T4A09
How can you determine the length of time that equipment can be powered from a battery?
A. Divide the watt-hour rating of the battery by the peak power consumption of the equipment
B. Divide the battery ampere-hour rating by the average current draw of the equipment
C. Multiply the watts per hour consumed by the equipment by the battery power rating
D. Multiply the square of the current rating of the battery by the input resistance of the equipment

Operating controls

To properly operate a transceiver, you need to know how to use the controls. Perhaps the most important transmitter control is microphone gain. Setting the gain too high will result in distorted audio.

T4B01
What is the effect of excessive microphone gain on SSB transmissions?
A. Frequency instability
B. Distorted transmitted audio
C. Increased SWR
D. All these choices are correct

You also need to know how to properly set the operating frequency of your transceiver. One reason for this is that setting the frequency of an FM receiver above or below a signal’s frequency will result in distorted receive audio.

T4B12
What is the result of tuning an FM receiver above or below a signal’s frequency?
A. Change in audio pitch
B. Sideband inversion
C. Generation of a heterodyne tone
D. Distortion of the signal’s audio

Many modern transceivers allow you to set the operating frequency in several different ways:

• Punching in a number on a keypad.

• Rotating the VFO knob.

• Storing it in a memory channel and then recalling it for quick access.

T4B02
Which of the following can be used to enter a transceiver’s operating frequency?
A. The keypad or VFO knob
B. The CTCSS or DTMF encoder
C. The Automatic Frequency Control
D. All these choices are correct

T4B04
What is a way to enable quick access to a favorite frequency or channel on your transceiver?
A. Enable the frequency offset
B. Store it in a memory channel
C. Enable the VOX
D. Use the scan mode to select the desired frequency

Transceivers that allow you to store frequencies in memory often have the ability to step through those frequencies, one at a time, stopping when a signal is received. This is called scanning and allows you to tune through a range of frequencies to check for activity.

T4B05
What does the scanning function of an FM transceiver do?
A. Checks incoming signal deviation
B. Prevents interference to nearby repeaters
C. Tunes through a range of frequencies to check for activity
D. Checks for messages left on a digital bulletin board

A common receiver control on VHF/UHF transceivers is the squelch control.

T4B03
How is squelch adjusted so that a weak FM signal can be heard?
A. Set the squelch threshold so that receiver output audio is on all the time
B. Turn up the audio level until it overcomes the squelch threshold
C. Turn on the anti-squelch function
D. Enable squelch enhancement

Another common setting on VHF/UHF transceivers is the offset frequency. This is especially important when operating repeaters.

T2A07
What is meant by “repeater offset”?
A. The difference between a repeater’s transmit and receive frequencies
B. The repeater has a time delay to prevent interference
C. The repeater station identification is done on a separate frequency
D. The number of simultaneous transmit frequencies used by a repeater

In recent years, radios that digitize one’s voice and then send the digitized voice over the air have become quite popular. The operating modes that these radios use are called digital modes. Two of the most popular digital modes are DMR (Digital Mobile Radio) and D-STAR (Digital Smart Technology for Amateur Radio).

One of the reasons digital modes are so popular is that the digitized voice information can not only be transmitted over the air, but also over the internet. To connect to other radio amateurs over the internet, digital mode radios can use a repeater that is connected to the internet or a digital mode hot spot that connect to the internet via a personal computer or smart phone with an internet connection.

T4A10
What function is performed with a transceiver and a digital mode hot spot?
A. Communication using digital voice or data systems via the internet
B. FT8 digital communications via AFSK
C. RTTY encoding and decoding without a computer
D. High-speed digital communications for meteor scatter

DMR has a feature called talkgroups. Talk groups are virtual channels, and when you access a talkgroup, your signal is routed to other radio amateurs who have also accessed that talkgroup, no matter where in the world they are. To use this feature, you must program your radio to properly access repeaters and the talkgroups. This programming information is contained in a DMR radio’s code plug.

T4B07
What does a DMR “code plug” contain?
A. Your call sign in CW for automatic identification
B. Access information for repeaters and talkgroups
C. The codec for digitizing audio
D. The DMR software version

T4B09
How is a specific group of stations selected on a digital voice transceiver?
A. By retrieving the frequencies from transceiver memory
B. By enabling the group’s CTCSS tone
C. By entering the group’s identification code
D. By activating automatic identification

Part of the information sent when you use a digital voice transceiver, be it a DMR or D-STAR radio, is your call sign. Before you use the radio, you must program the radio with your call sign.

T4B11
Which of the following must be programmed into a D-STAR digital transceiver before transmitting?
A. Your call sign
B. Your output power
C. The codec type being used
D. All these choices are correct

HF transceivers have many controls not found on VHF/UHF FM transceivers. For example, they are often equipped with a variety of different filters. The reason for this is that using the appropriate filter for the mode you are operating can make operating a lot easier.

T4B08
What is the advantage of having multiple receive bandwidth choices on a multimode transceiver?
A. Permits monitoring several modes at once by selecting a separate filter for each mode
B. Permits noise or interference reduction by selecting a bandwidth matching the mode
C. Increases the number of frequencies that can be stored in memory
D. Increases the amount of offset between receive and transmit frequencies

T4B10
Which of the following receiver filter bandwidths provides the best signal-to-noise ratio for SSB reception?
A. 500 Hz
B. 1000 Hz
C. 2400 Hz
D. 5000 Hz

A common receiver control on HF transceivers is the Receiver Incremental Tuning, or RIT, control. Its purpose is to set the receive frequency slightly off from the transmit frequency.

T4B06
Which of the following controls could be used if the voice pitch of a single-sideband signal returning to your CQ call seems too high or low?
A. The AGC or limiter
B. The bandwidth selection
C. The tone squelch
D. The RIT or Clarifier

A common transmitter control is push-to-talk, or PTT. Most of the time PTT refers to an actual switch on the microphone that an operator must push to begin transmitting, but it also refers to the name of a signal line on a transceiver’s accessory socket that can be used to automatically switch a transceiver into transmit mode.

T7A07
What is the function of a transceiver’s PTT input?
A. Input for a key used to send CW
B. Switches transceiver from receive to transmit when grounded
C. Provides a transmit tuning tone when grounded
D. Input for a preamplifier tuning tone

Antennas and feed lines

Antenna types

The most common, and perhaps the simplest, antenna is the half-wave dipole antenna. As the name suggests, it measures close to one half wavelength from one end of the antenna to the other. Because half-wave dipole antennas can be quite long—a 40m half-wave dipole antenna, for example, is about 66 feet long—they are normally mounted horizontally between two vertical supports.

T9A03
Which of the following describes a simple dipole oriented parallel to Earth’s surface?
A. A ground-wave antenna
B. A horizontally polarized antenna
C. A travelling-wave antenna
D. A vertically polarized antenna

When putting up a dipole antenna, you should consider the orientation of the antenna because it radiates better in some directions than others.

T9A10
In which direction does a half-wave dipole antenna radiate the strongest signal?
A. Equally in all directions
B. Off the ends of the antenna
C. In the direction of the feed line
D. Broadside to the antenna

So, for example, if you live in Kansas, you might want to orient the antenna so that the wire runs north to south. The antenna will then radiate best east and west, meaning that you’ll be able to cover most of the U.S.

The length of a dipole antenna is actually about 5% shorter than the value that you would calculate using the formula wavelength (m) = 300 / frequency (MHz). The reason for this is that there will be some stray capacitance between the wire and the ground and other objects near the antenna. Let’s take a look at an example.

T9A09
What is the approximate length, in inches, of a half-wavelength 6 meter dipole antenna?
A. 6
B. 50
C. 112
D. 236

Here’s how to make this calculation. One half wavelength is 3 m. 3 m x 39.4 in/m = 118.2 inches. Since the length of the antenna is about 5% shorter than this calculated value, the approximate length of the antenna will be 118.2 inches x 0.95, or about 112 inches.

Once you have built a dipole antenna, chances are it won’t be resonant on the frequency you want. To tune the antenna, you need to determine its resonant frequency and then make it longer or shorter. To decrease the resonant frequency of an antenna, you lengthen it, because the wavelength is longer. Conversely, to increase the resonant frequency, you shorten the antenna.

T9A05
Which of the following increases the resonant frequency of a dipole antenna?
A. Lengthening it
B. Inserting coils in series with radiating wires
C. Shortening it
D. Adding capacitive loading to the ends of the radiating wires

The final length will depend on the height at which you mount the antenna and any trees or buildings that are nearby.

Perhaps the second-most popular type of amateur radio antenna is the quarter-wave vertical antenna. The radiator of a vertical antenna is mounted perpendicular to the Earth. This makes it vertically-polarized, because the electric field will have the same orientation as the antenna’s radiator.

Like the half-wave dipole antenna, the length of a quarter-wave vertical antenna will be about 5% shorter than the calculated quarter wavelength.

T9A08
What is the approximate length, in inches, of a quarter-wavelength vertical antenna for 146 MHz?
A. 112
B. 50
C. 19
D. 12

The wavelength of a 146 MHz radio wave is approximately 2 m. One quarter of a wavelength is therefore 0.5 m. 0.5 m x 39.4 in/m = 19.7 in. 19.7 in x 0.95 ≈ 19 in.

Because full-size, half-wave or quarter-wave HF antennas can be very long, many amateurs use a technique called “loading” to shorten them. You can use either inductors or capacitors to load an antenna, but the most common way is to use an inductor. In either case, loading an antenna makes it seem electrically longer to a signal at the antenna feed point.

T9A02
Which of the following describes a type of antenna loading?
A. Electrically lengthening by inserting inductors in radiating elements
B. Inserting a resistor in the radiating portion of the antenna to make it resonant
C. Installing a spring in the base of a mobile vertical antenna to make it more flexible
D. Strengthening the radiating elements of a beam antenna to better resist wind damage

While this technique does allow you to shorten an antenna, the shortened antenna will not be as efficient as a full-size antenna.

Many amateurs use directional or beam antennas. Beam antennas concentrate the power that is applied to them in onedirection, thereby increasing the signal strength in that direction, when compared to a reference antenna, such as a dipole antenna. We call this increase in signal strength antenna gain. There are many different types of beam antennas, including the Yagi, the quad, and the dish antenna.

T9A01
What is a beam antenna?
A. An antenna built from aluminum I-beams
B. An omnidirectional antenna invented by Clarence Beam
C. An antenna that concentrates signals in one direction
D. An antenna that reverses the phase of received signals

T9A11
What is antenna gain?
A. The additional power that is added to the transmitter power
B. The additional power that is required in the antenna when transmitting on a higher frequency
C. The increase in signal strength in a specified direction compared to a reference antenna
D. The increase in impedance on receive or transmit compared to a reference antenna

T9A06
Which of the following types of antenna offers the greatest gain?
A. 5/8 wave vertical
B. Isotropic
C. J pole
D. Yagi

Most handheld VHF and UHF transceivers come with short, flexible antennas called “rubber duck” antennas. These antennas use inductive loading to make them shorter than a full-sized antenna. Loading them like this makes them less efficient than a full-sized quarter-wavelength vertical antenna.

T9A04
What is a disadvantage of the short, flexible antenna supplied with most handheld radio transceivers, compared to a full-sized quarter-wave antenna?
A. It has low efficiency
B. It transmits only circularly polarized signals
C. It is mechanically fragile
D. All these choices are correct

This disadvantage is compounded if you try to use a handheld VHF transceiver inside a vehicle. The shielding effect of the vehicle’s metal frame will prevent some of your signal from getting outside the vehicle and block some of the signal from a repeater or other station from reaching the antenna inside the vehicle.

T9A07
What is a disadvantage of using a handheld VHF transceiver with a flexible antenna inside a vehicle?
A. Signal strength is reduced due to the shielding effect of the vehicle
B. The bandwidth of the antenna will decrease, increasing SWR
C. The SWR might decrease, decreasing the signal strength
D. All these choices are correct

A better option is to use an externally-mounted antenna. A popular choice for an externally-mounted mobile antenna is the 5/8-wavelength vertical antenna. One reason that it is a popular choice, is that it has more gain than a 1/4-wavelength antenna.

T9A12
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

Feed lines and connectors

Feed lines connect radios to antennas. There are many different types of feed lines, including coaxial cable, ladder line, twin lead, and open-wire feed line, but coaxial cable is the most common type.

T9B03
Why is coaxial cable the most common feed line for amateur radio antenna systems?
A. It is easy to use and requires few special installation considerations
B. It has less loss than any other type of feed line
C. It can handle more power than any other type of feed line
D. It is less expensive than any other type of feed line

Perhaps the most important consideration when choosing a feed line is the impedance of the feed line. In general, you should match the impedance of the feed line to the output impedance of the transmitter and the input impedance of the antenna.

T5C12
What is impedance?
A. The opposition to AC current flow
B. The inverse of resistance
C. The Q or Quality Factor of a component
D. The power handling capability of a component

T5C05
What is the unit of impedance?
A. The volt
B. The ampere
C. The coulomb
D. The ohm

Most amateur radio transmitters have an output impedance of 50 ohms, and most antennas have an input impedance close to 50 ohms. Because this is the case, most coaxial cable used in amateur radio stations has an impedance of 50 ohms.

T9B02
What is the most common impedance of coaxial cables used in amateur radio?
A. 8 ohms
B. 50 ohms
C. 600 ohms
D. 12 ohms

RG-58 and RG-213 are two types of coaxial cable often used in amateur radio stations. Both have an impedance of 50 ohms.

Despite being the most popular type of feedline for amateur radio stations, coaxial cable does have some disadvantages. One of them is that it may be lossy at high frequencies. Some coax cable types have more loss than others.

T9B05
What happens as the frequency of a signal in coaxial cable is increased?
A. The characteristic impedance decreases
B. The loss decreases
C. The characteristic impedance increases
D. The loss increases

T9B10
What is the electrical difference between RG-58 and RG-213 coaxial cable?
A. There is no significant difference between the two types
B. RG-58 cable has two shields
C. RG-213 cable has less loss at a given frequency
D. RG-58 cable can handle higher power levels

In general, the smaller the diameter of the coaxial cable, the higher the losses will be at higher frequencies. And, the longer the feed line, the higher the losses. So, for example, using RG-58 coax as the feed line for an 80 m dipole might be just fine, but you don’t want to use 50 feet of RG-58 to connect your 440 MHz FM transceiver to an antenna on your roof or on a tower.

Even RG-213 coaxial cable is not really the best choice for use at VHF and UHF frequencies. Most repeaters, for example, use air-insulated hard line coaxial cable for the feed line.

T9B11
Which of the following types of feed line has the lowest loss at VHF and UHF?
A. 50-ohm flexible coax
B. Multi-conductor unbalanced cable
C. Air-insulated hardline
D. 75-ohm flexible coax

Many other factors, including water intrusion, high SWR, and multiple connectors in line can cause losses in a coaxial feed line.

T9B08
Which of the following is a source of loss in coaxial feed line?
A. Water intrusion into coaxial connectors
B. High SWR
C. Multiple connectors in the line
D. All these choices are correct

Moisture contamination not only causes higher feed line losses. If not addressed, it can also cause coaxial cables to fail.

T7C09
Which of the following causes failure of coaxial cables?
A. Moisture contamination
B. Solder flux contamination
C. Rapid fluctuation in transmitter output power
D. Operation at 100% duty cycle for an extended period

One way that moisture enters a cable is via cracks in the cable’s outer jacket caused by ultraviolet light.

T7C10
Why should the outer jacket of coaxial cable be resistant to ultraviolet light?
A. Ultraviolet resistant jackets prevent harmonic radiation
B. Ultraviolet light can increase losses in the cable’s jacket
C. Ultraviolet and RF signals can mix, causing interference
D. Ultraviolet light can damage the jacket and allow water to enter the cable

Air-insulated hard line is also susceptible to moisture problems.

T7C11
What is a disadvantage of air core coaxial cable when compared to foam or solid dielectric types?
A. It has more loss per foot
B. It cannot be used for VHF or UHF antennas
C. It requires special techniques to prevent moisture in the cable
D. It cannot be used at below freezing temperatures

PL-259 connectors are the most common type of connectors used on coaxial cables in amateur radio stations.

T9B07
Which of the following is true of PL-259 type coax connectors?
A. They are preferred for microwave operation
B. They are watertight
C. They are commonly used at HF and VHF frequencies
D. They are a bayonet-type connector

One problem with PL-259 connectors is that they are not the most suitable connector when operating at higher frequencies. Type N connectors are a much better choice for UHF frequencies.

T9B06
Which of the following RF connector types is most suitable for frequencies above 400 MHz?
A. UHF (PL-259/SO-239)
B. Type N
C. RS-213
D. DB-25

Coaxial cable connectors can be a real pain to install properly and are a frequent cause of failure. When installing a feed line, make sure that your coaxial connectors are crimped or soldered properly and that they make solid connections with one another.

T9B09
What can cause erratic changes in SWR?
A. Local thunderstorm
B. Loose connection in the antenna or feed line
C. Over-modulation
D. Overload from a strong local station

Standing wave ratio and antenna measurements

Standing wave ratio, or SWR, is a term you’ll often hear when talking about antennas and feed lines. It is a measure of how well a load, such as an antenna, is matched to a transmission line. When we say that an antenna is matched to a transmission line, we mean that the impedance of the transmission line is equal to the impedance of the antenna. If you measure the SWR of a perfectly-matched antenna system, the SWR meter will read 1:1. The higher the SWR reading, the greater the mismatch between the antenna and the transmission line.

T9B12
What is standing wave ratio (SWR)?
A. A measure of how well a load is matched to a transmission line
B. The ratio of amplifier power output to input
C. The transmitter efficiency ratio
D. An indication of the quality of your station’s ground connection

T7C04
What reading on an SWR meter indicates a perfect impedance match between the antenna and the feed line?
A. 50:50
B. Zero
C. 1:1
D. Full Scale

T7C06
What does an SWR reading of 4:1 indicate?
A. Loss of -4 dB
B. Good impedance match
C. Gain of +4 dB
D. Impedance mismatch

When the feed line impedance matches the antenna input impedance, the SWR will be low. Low SWR on a coaxial cable feed line is a good thing because when the feed line impedance matches the antenna input impedance, signal losses are low, meaning that the antenna will radiate more power.

T9B01
What is a benefit of low SWR?
A. Reduced television interference
B. Reduced signal loss
C. Less antenna wear
D. All these choices are correct

The bigger the mismatch is between the feed line and the load, the higher the SWR will be. The higher the SWR, the more power is lost in the feed line. Power converted into heat is not radiated by the antenna, meaning your radiated signal will be weaker.

T7C07
What happens to power lost in a feed line?
A. It increases the SWR
B. It is radiated as harmonics
C. It is converted into heat
D. It distorts the signal

Most amateur radio transceivers today will reduce output power if the antenna system SWR is high. The reason for this is to protect the radio from being damaged by reflected power.

T7C05
Why do most solid-state transmitters reduce output power as SWR increases beyond a certain level?
A. To protect the output amplifier transistors
B. To comply with FCC rules on spectral purity
C. Because power supplies cannot supply enough current at high SWR
D. To lower the SWR on the transmission line

An SWR meter is not the only way to measure SWR. You can also measure SWR with a directional wattmeter.

T7C08
Which instrument can be used to determine SWR?
A. Voltmeter
B. Ohmmeter
C. Iambic pentameter
D. Directional wattmeter

When using a directional wattmeter, you first measure the forward power, then the reflected power, and using those two values, calculate the SWR.

Another test instrument that you can use to measure the SWR of an antenna system is the antenna analyzer. The SWR of an antenna system will be 1:1 at the resonant frequency.

T7C02
Which of the following is used to determine if an antenna is resonant at the desired operating frequency?
A. A VTVM
B. An antenna analyzer
C. A Q meter
D. A frequency counter

Some antenna analyzers will also let you measure capacitive reactance and inductive reactance, and also be used as an RF signal generator. These capabilities may be useful in applications other than antenna analysis.

If an antenna’s impedance is not 50 ohms, the impedance at the transmitter end of a feed line will not be 50 ohms. Don’t worry, though. You can use a device called an antenna tuner or antenna coupler to transform the impedance from whatever it happens to be to 50 ohms. We call this process impedance matching.

T9B04
What is the major function of an antenna tuner (antenna coupler)?
A. It matches the antenna system impedance to the transceiver’s output impedance
B. It helps a receiver automatically tune in weak stations
C. It allows an antenna to be used on both transmit and receive
D. It automatically selects the proper antenna for the frequency band being used

In addition to instruments that make antenna measurements, it’s helpful to have an instrument that can simulate an antenna. That’s the purpose of a dummy load. Basically, a dummy load is just a big 50 Ω resistor that provides a known impedance to the transmitter and converts the transmitter output power into heat so that it does not get radiated. If a transmitter operates normally when a dummy load is connected to it, you can be reasonably sure that your transmitter is good.

T7C01
What is the primary purpose of a dummy load?
A. To prevent transmitting signals over the air when making tests
B. To prevent over-modulation of a transmitter
C. To improve the efficiency of an antenna
D. To improve the signal-to-noise ratio of a receiver

T7C03 (B)
What does a dummy load consist of?
A. A high-gain amplifier and a TR switch
B. A non-inductive resistor mounted on a heat sink
C. A low-voltage power supply and a DC relay
D. A 50-ohm reactance used to terminate a transmission line

Here’s the third chapter from the 2022 version of the No Nonsense Technician Class License Study Guide……….Dan

Frequency, wavelength, and the electromagnetic spectrum

Radio waves are what amateur radio is all about. Amateur radio operators generate them and send them off into space. Then, we capture them and demodulate them.

Radio waves are also called electromagnetic waves because they consist of both an electric field and a magnetic field. The two fields are at right angles to one another as they travel through space.

T3B03
What are the two components of a radio wave?
A. Impedance and reactance
B. Voltage and current
C. Electric and magnetic fields
D. Ionizing and non-ionizing radiation

T3B01
What is the relationship between the electric and magnetic fields of an electromagnetic wave?
A. They travel at different speeds
B. They are in parallel
C. They revolve in opposite directions
D. They are at right angles

All electromagnetic waves, including radio waves, travel at the speed of light, or 300 million meters per second.

T3B04
What is the velocity of a radio wave traveling through free space?
A. Speed of light
B. Speed of sound
C. Speed inversely proportional to its wavelength
D. Speed that increases as the frequency increases

T3B11
What is the approximate velocity of a radio wave in free space?
A. 150,000 meters per second
B. 300,000,000 meters per second
C. 300,000,000 miles per hour
D. 150,000 miles per hour

An important characteristic of a radio wave is its frequency, or the number of cycles per second. As mentioned earlier, the unit of frequency is the Hertz. We abbreviate Hertz as Hz, and one Hz is one cycle per second.

A characteristic of a radio wave that is related to frequency is its wavelength. A wavelength is the distance that a radio wave travels during one cycle. Because radio waves travel at the speed of light, or 300,000,000 meters per second, the wavelength is 300,000,000 divided by the frequency. To make this easier to calculate, you can divide both the speed of light and the frequency by one million. That makes the equation:

wavelength (m) = 300/f (MHz)

The converse of this equation is:

f (MHz) = 300/wavelength (m)

As you can see from the equations, the lower the frequency, the longer the wavelength, and vice versa, the higher the frequency, the shorter the wavelength.

T3B06
What is the formula for converting frequency to approximate wavelength in meters?
A. Wavelength in meters equals frequency in hertz multiplied by 300
B. Wavelength in meters equals frequency in hertz divided by 300
C. Wavelength in meters equals frequency in megahertz divided by 300
D. Wavelength in meters equals 300 divided by frequency in megahertz

T3B05
What is the relationship between wavelength and frequency?
A. Wavelength gets longer as frequency increases
B. Wavelength gets shorter as frequency increases
C. Wavelength and frequency are unrelated
D. Wavelength and frequency increase as path length increases

In amateur radio, we sometimes use the frequency and sometimes the wavelength when talking about a radio signal. We use wavelength, for example, when we refer to the amateur radio bands. The 2 m amateur radio band, for example, spans 144 MHz to 148 MHz. A radio wave with a frequency of 148 MHz, would have a wavelength of 2.03 meters.

T3B07
In addition to frequency, which of the following is used to identify amateur radio bands?
A. The approximate wavelength in meters
B. Traditional letter/number designators
C. Channel numbers
D. All these choices are correct

For convenience, we split the entire range of radio frequencies into sub-ranges, including high frequency (HF), very high frequency (VHF), and ultra high frequency (UHF).

T3B10
What frequency range is referred to as HF?
A. 300 to 3000 MHz
B. 30 to 300 MHz
C. 3 to 30 MHz
D. 300 to 3000 kHz

T3B08
What frequency range is referred to as VHF?
A. 30 kHz to 300 kHz
B. 30 MHz to 300 MHz
C. 300 kHz to 3000 kHz
D. 300 MHz to 3000 MHz

T3B09
What frequency range is referred to as UHF?
A. 30 to 300 kHz
B. 30 to 300 MHz
C. 300 to 3000 kHz
D. 300 to 3000 MHz

A radio signal of any frequency is called a radio frequency, or RF, signal.

T5C06
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

Properties of radio waves and propagation modes

As amateur radio operators, we should always try to use the right frequency and the right mode when communicating. To do this, we need to know how radio signals travel from one point to another and what effect frequency, our antennas and even our location have on signal propagation.

Communications at VHF and UHF frequencies are generally “line-of-sight” communications. This means they normally travel in a straight line from the transmitter to the receiver. For this reason, they are normally used for local communications.

Because VHF and UHF signals are line-of-sight, at some distance, the signals will be blocked by the curvature of the Earth. The maximum distance for line-of-sight communications is called the radio horizon. The radio horizon extends somewhat farther than the visual horizon.

T3C11
Why is the radio horizon for VHF and UHF signals more distant than the visual horizon?
A. Radio signals move somewhat faster than the speed of light
B. Radio waves are not blocked by dust particles
C. The atmosphere refracts radio waves slightly
D. Radio waves are blocked by dust particles

T3C01
Why are simplex UHF signals rarely heard beyond their radio horizon?
A. They are too weak to go very far
B. FCC regulations prohibit them from going more than 50 miles
C. UHF signals are usually not propagated by the ionosphere
D. UHF signals are absorbed by the ionospheric D region

Some signals bounce off the ionosphere. This gives them the ability to travel much further than line of sight. We’ll talk more about the ionosphere later.

One problem often encountered when using VHF and UHF frequencies is multipath propagation. Multipath propagation occurs when your signals arrive at a receiving station via two or more paths. Since the signal paths may be different lengths, the signals may arrive out of phase and cancel one another or arrive in phase and reinforce one another. Moving an antenna only a few feet, say when you’re operating mobile, can cause the received signal strength to vary greatly.

T3A01
Why do VHF signal strengths sometimes vary greatly when the antenna is moved only a few feet?
A. The signal path encounters different concentrations of water vapor
B. VHF ionospheric propagation is very sensitive to path length
C. Multipath propagation cancels or reinforces signals
D. All these choices are correct

This can be a real problem for mobile operation, as your transmitter and antenna location is constantly changing. This means that the signal strength at the receiving station constantly changes as well. This rapid fluctuation in received signal strength is sometimes called picket fencing.

T3A06
What is the meaning of the term “picket fencing”?
A. Alternating transmissions during a net operation
B. Rapid flutter on mobile signals due to multipath propagation
C. A type of ground system used with vertical antennas
D. Local vs long-distance communications

Because it can cause signal strength to vary greatly, multipath propagation affects both voice and digital transmissions. Since reliable digital transmissions rely on the signals being relatively constant and strong, multipath propagation can cause errors to occur.

T3A10
What effect does multipath propagation have on data transmissions?
A. Transmission rates must be increased by a factor equal to the number of separate paths observed
B. Transmission rates must be decreased by a factor equal to the number of separate paths observed
C. No significant changes will occur if the signals are transmitted using FM
D. Error rates are likely to increase

Knowing how VHF and UHF signals propagate can help you communicate even in adverse conditions. When trying to use a repeater, for example, you may find yourself in a place where a direct path to the repeater is not possible. If you find yourself in this situation, you could try using a directional antenna and bounce your signal off buildings or other obstructions.

T3A05
When using a directional antenna, how might your station be able to communicate with a distant repeater if buildings or obstructions are blocking the direct line of sight path?
A. Change from vertical to horizontal polarization
B. Try to find a path that reflects signals to the repeater
C. Try the long path
D. Increase the antenna SWR

Another phenomenon you might use when a direct path to a repeater is not possible is “knife-edge” diffraction. You might be able to use this phenomenon to get your signal around a building in an urban setting or over a mountain peak in an outside setting.

T3C05
Which of the following effects may allow radio signals to travel beyond obstructions between the transmitting and receiving stations?
A. Knife-edge diffraction
B. Faraday rotation
C. Quantum tunneling
D. Doppler shift

A condition that could impede the transmission of UHF and microwave signals is heavy vegetation. So, keep your antennas out of trees or above trees.

T3A02
What is the effect of vegetation on UHF and microwave signals?
A. Knife-edge diffraction
B. Absorption
C. Amplification
D. Polarization rotation

Antenna polarization is important at VHF and UHF frequencies. How you mount an antenna directly affects its polarization. When the radiating element of an antenna is vertical, the transmitted radio waves will have a vertical polarization. When the radiating element of an antenna is horizontal, the radio waves will have a horizontal polarization.

T3B02
What property of a radio wave defines its polarization?
A. The orientation of the electric field
B. The orientation of the magnetic field
C. The ratio of the energy in the magnetic field to the energy in the electric field
D. The ratio of the velocity to the wavelength

T3A04
What happens when antennas at opposite ends of a VHF or UHF line of sight radio link are not using the same polarization?
A. The modulation sidebands might become inverted
B. Received signal strength is reduced
C. Signals have an echo effect
D. Nothing significant will happen

When using a repeater, vertical polarization is most often used. So, when using a handheld transceiver, make sure to hold it so that your antenna is straight up and down. Different activities use different antenna polarizations, though.

T3A03
What antenna polarization is normally used for long-distance CW and SSB contacts on the VHF and UHF bands?
A. Right-hand circular
B. Left-hand circular
C. Horizontal
D. Vertical

The reason for this is that operators transmitting CW and SSB signals are often using what are called beam antennas, and it’s much easier to mount and operate beam antennas horizontally than it is to mount them vertically.

Even though VHF communications are most often line-of-sight, there are some propagation modes that make it possible to communicate over long distances. For example, sometimes VHF signals will bounce off the E layer of the ionosphere. This phenomenon is called “sporadic E” propagation because it happens only sporadically.

T3C04
Which of the following types of propagation is most commonly associated with occasional strong signals on the 10, 6, and 2 meter bands from beyond the radio horizon?
A. Backscatter
B. Sporadic E
C. D region absorption
D. Gray-line propagation

Other interesting propagation phenomena at VHF frequencies include auroral backscatter, meteor scatter, tropospheric scatter, and tropospheric ducting. Bouncing signals off the earth’s aurora is very interesting to do, but the signals usually become distorted and signal strength can vary greatly. This is because the aurora itself is constantly changing.

T3C03
What is a characteristic of VHF signals received via auroral backscatter?
A. They are often received from 10,000 miles or more
B. They are distorted and signal strength varies considerably
C. They occur only during winter nighttime hours
D. They are generally strongest when your antenna is aimed west

Some hams also bounce signals off meteor showers. This propagation mode is called meteor scatter. Meteor scatter propagation is most pronounced on the 6-meter band.

T3C07
What band is best suited for communicating via meteor scatter?
A. 33 centimeters
B. 6 meters
C. 2 meters
D. 70 centimeters

One question that I often get is whether or not the weather affects radio wave propagation. The short answer is no, but there are, of course, exceptions to this rule. One way that weather can affect radio propagation is when there is a temperature inversion in the atmosphere. A temperature inversion occurs when a layer of cooler air gets trapped below a layer of warmer air in the troposphere. The troposphere is the lowest region of the atmosphere, extending from the earth’s surface to a height of about 6–10 km..

When this happens, a tropospheric duct may form. VHF signals entering this duct may propagate through the duct for hundreds of miles.

T3C06
What type of propagation is responsible for allowing over-the-horizon VHF and UHF communications to ranges of approximately 300 miles on a regular basis?
A. Tropospheric ducting
B. D region refraction
C. F2 region refraction
D. Faraday rotation

T3C08
What causes tropospheric ducting?
A. Discharges of lightning during electrical storms
B. Sunspots and solar flares
C. Updrafts from hurricanes and tornadoes
D. Temperature inversions in the atmosphere

Another exception to the rule occurs at microwave frequencies. Precipitation, including rain, snow, or ice can absorb microwave signals, thereby decreasing range. At lower frequencies, however, precipitation has little or no effect on propagation.

T3A07
What weather condition might decrease range at microwave frequencies?
A. High winds
B. Low barometric pressure
C. Precipitation
D. Colder temperatures

T3A12
What is the effect of fog and rain on signals in the 10 meter and 6 meter bands?
A. Absorption
B. There is little effect
C. Deflection
D. Range increase

Units and terms: current, voltage, and resistance; alternating and direct current; conductors and insulators

Figure 1 shows a simple electric circuit. It consists of a voltage source (in this case a battery, labeled V), a resistor (labeled R), and some wires to connect the battery to the resistor. When connected in this way, the voltage across the battery will cause a current (labeled I) to flow through the circuit. Voltage (V), current (I), and resistance (R) are the three basic parameters of an electric circuit.

Voltage is the force that causes electrons to flow in a circuit. Voltage is measured in volts, and we use the letter V to represent both the force and the units.

T5A05
What is the electrical term for the force that causes electron flow?
A. Voltage
B. Ampere-hours
C. Capacitance
D. Inductance

Current is the flow of electrons in a circuit. In Figure 1, the letter I stands for current. Current flows from the positive (+) terminal of the voltage source through the circuit to the negative terminal of the voltage source. Current is measured in amperes, and we use the letter A to stand for amperes.

T5A03
What is the name for the flow of electrons in an electric circuit?
A. Voltage
B. Resistance
C. Capacitance
D. Current

T5A01
Electrical current is measured in which of the following units?
A. Volts
B. Watts
C. Ohms
D. Amperes

Because the polarity of the battery voltage in the circuit never changes, the current will flow in only one direction through the circuit. We call this direct current, or DC. Batteries supply direct current, or simply, DC.

The type of current you get out of a wall socket is different from the current that you get from a battery. We call it alternating current because the voltage and current are constantly changing.

Figure 2 shows an alternating current waveform. That is to say it shows how the voltage changes over time. For this particular waveform, the voltage starts at 0 V, increases to a positive peak voltage, then decreases to a negative peak voltage, and then begins increasing again, until it once again reaches 0 V. This process repeats over and over.

T5A09
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

One of the most important parameters of an alternating current is its frequency. The frequency of an alternating current is the number of times per second that an alternating current makes a complete cycle, where a cycle is the portion of an alternating current waveform that repeats over and over. The frequency of the alternating current that you get from a wall socket in your home is 60 cycles per second, or in engineering terms, 60 hertz (Hz). 1 Hz is equal to one cycle per second.

T5A12
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

T5A06
What is the unit of frequency?
A. Hertz
B. Henry
C. Farad
D. Tesla

Resistance is the third basic parameter of an electric circuit. As the name implies, resistance opposes the flow of current in a circuit. The higher the resistance, the smaller the current, for a given voltage. This applies to direct current, alternating current, and RF current, which is alternating current with a high frequency. We use the letter R to stand for resistance. Resistance is measured in ohms, and we use the Greek letter omega (Ω) to stand for ohms.

T5A04
What are the units of electrical resistance?
A. Siemens
B. Mhos
C. Ohms
D. Coulombs

T5A11
What type of current flow is opposed by resistance?
A. Direct current
B. Alternating current
C. RF current
D. All these choices are correct

To connect components in an electric circuit, we generally use copper wires because they conduct electrical current well or, in other words, have a low resistance. Metals generally are good conductors because they have many free electrons, and as a result offer low resistance to current flow.

T5A07
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

Silver is actually a better conductor than copper, but copper is a lot less expensive than silver. Often, you will see gold used as a conductor. Although gold is not as good a conductor as either copper or silver, it doesn’t corrode like copper or silver. That makes it a good choice for switch or connector contacts.

Many times we need a material that does not conduct current very well. We call these materials insulators, and insulators have a high resistance. Plastics and glass are commonly used insulators.

T5A08
Which of the following is a good electrical insulator?
A. Copper
B. Glass
C. Aluminum
D. Mercury

Ohm’s Law: formulas and usage

Hams obey Ohm’s Law!

Ohm’s Law is the relationship between voltage, current, and resistance in an electrical circuit. When you know any two of these values, you can calculate the third.

The most basic equation for Ohm’s Law is V = I × R. In other words, when you know the current (I) flowing through a circuit and the resistance (R) of the circuit, you can calculate the voltage across the circuit by multiplying these two values.

T5D02
What formula is used to calculate voltage in a circuit?
A. V = I x R
B. V = I / R
C. V = I + R
D. V = I – R

Using simple algebra, you can derive the other two forms of this equation: R = V / I and I = V / R. These two equations let you calculate the resistance in a circuit if you know the voltage and current or the current in a circuit if you know the voltage and resistance.

T5D03
What formula is used to calculate resistance in a circuit?
A. R = V x I
B. R = V / I
C. R = V + I
D. R = V – I

T5D01
What formula is used to calculate current in a circuit?
A. I = V x R
B. I = V / R
C. I = V + R
D. I = V – R

Now, let’s look at some examples of how to apply Ohm’s Law.

T5D04
What is the resistance of a circuit in which a current of 3 amperes flows when connected to 90 volts?
A. 3 ohms
B. 30 ohms
C. 93 ohms
D. 270 ohms

Here’s how to calculate this answer: R = V / I = 90 V / 3 A = 30 Ω

T5D05
What is the resistance of a circuit for which the applied voltage is 12 volts and the current flow is 1.5 amperes?
A. 18 ohms
B. 0.125 ohms
C. 8 ohms
D. 13.5 ohms

R = V / I = 12 V / 1.5 A = 8 Ω

T5D06
What is the resistance of a circuit that draws 4 amperes from a 12-volt source?
A. 3 ohms
B. 16 ohms
C. 48 ohms
D. 8 ohms

R = V / I = 12 V / 4 A = 3 Ω.

Now, let’s look at another form of the Ohm’s Law equation, I = V / R to calculate the current in a circuit.

T5D07
What is the current in a circuit with an applied voltage of 120 volts and a resistance of 80 ohms?
A. 9600 amperes
B. 200 amperes
C. 0.667 amperes
D. 1.5 amperes

I = V / R = 120 V / 80 Ω = 1.5 A

T5D08
What is the current through a 100-ohm resistor connected across 200 volts?
A. 20,000 amperes
B. 0.5 amperes
C. 2 amperes
D. 100 amperes

I = V / R = 200 V / 100 Ω = 2 A

T5D09
What is the current through a 24-ohm resistor connected across 240 volts?
A. 24,000 amperes
B. 0.1 amperes
C. 10 amperes
D. 216 amperes

I = V / R = 240 V / 24 Ω = 10 A

Now, let’s look at the third form of the Ohm’s Law equation, E = I × R to calculate the voltage across a circuit.

T5D10
What is the voltage across a 2-ohm resistor if a current of 0.5 amperes flows through it?
A. 1 volt
B. 0.25 volts
C. 2.5 volts
D. 1.5 volts

V = I × R = 0.5 A × 2 Ω = 1 V

T5D11
What is the voltage across a 10-ohm resistor if a current of 1 ampere flows through it?
A. 1 volt
B. 10 volts
C. 11 volts
D. 9 volts

V = I × R = 1 A × 10 Ω = 10 V

T5D12
What is the voltage across a 10-ohm resistor if a current of 2 amperes flows through it?
A. 8 volts
B. 0.2 volts
C. 12 volts
D. 20 volts

V = I × R = 2 A × 10 Ω = 20 V

Series and parallel circuits

Now, let’s consider circuits with two resistors instead of just a single resistor. There are two ways in which the two resistors can be connected: in series or in parallel. Figure 3 shows a series circuit.

There is only one path for the current to flow, so the same current flows through both resistors. If R1 = R2, then the voltage will be the same across both resistors, because the same current flows through both resistors. If R1 does not equal R2, however, the voltages will be different. In either case, the sum of the two voltages will equal the voltage of the voltage source.

T5D13
In which type of circuit is DC current the same through all components?
A. Series
B. Parallel
C. Resonant
D. Branch

In a parallel circuit, shown in Figure 4, both resistors are connected directly to the voltage source.

Because both components are connected directly to the voltage source, the voltage across them will be the same. This voltage will cause currents to flow in each of the resistors. I1 = V/R1, and I2 = V/R2. The total current, I, is equal to I1 + I2. If R1 = R2, then the same current flows through both resistors. If the resistors have different values, then I1 will be different from I2.

T5D14
In which type of circuit is voltage the same across all components?
A. Series
B. Parallel
C. Resonant
D. Branch

DC power

Power is the rate at which electrical energy is generated or consumed. Power is measured in watts. We use the letter P to stand for power and the letter W to stand for watts.

T5A10
Which term describes the rate at which electrical energy is used?
A. Resistance
B. Current
C. Power
D. Voltage

T5A02
Electrical power is measured in which of the following units?
A. Volts
B. Watts
C. Watt-hours
D. Amperes

To calculate power, we multiply the voltage across a circuit by the current flowing through the circuit. We write this equation P = V × I.

T5C08
What is the formula used to calculate electrical power (P) in a DC circuit?
A. P = V x I
B. P = V / I
C. P = V – I
D. P = V + I

Here are some examples:

T5C09
How much power is delivered by a voltage of 13.8 volts DC and a current of 10 amperes?
A. 138 watts
B. 0.7 watts
C. 23.8 watts
D. 3.8 watts

The calculation for this question is P = V × I = 13.8 V × 10 A = 138 W.

T5C10
How much power is delivered by a voltage of 12 volts DC and a current of 2.5 amperes?
A. 4.8 watts
B. 30 watts
C. 14.5 watts
D. 0.208 watts

The calculation for this question is P = V × I = 12 V × 2.5 A = 30 W.

Just as with Ohm’s Law, you can use algebra to come up with other forms of this equation to calculate the voltage if you know the power and the current, or to calculate the current if you know the power and the voltage. The formula to calculate the current, if you know the power and the voltage, is I = P / V.

T5C11
How much current is required to deliver 120 watts at a voltage of 12 volts DC?
A. 0.1 amperes
B. 10 amperes
C. 12 amperes
D. 132 amperes

The calculation for this question is I = P / V = 120 W / 12 V = 10 A.

Math for electronics and conversion of electrical units

When dealing with electrical parameters such as voltage, resistance, current, and power, we use a set of prefixes to denote various orders of magnitude:

• milli- is the prefix used to denote 1 one-thousandth of a quantity. A milliampere, for example, is 1 one-thousandth of an ampere, or 0.001 A. Often, the letter m is used instead of the prefix milli-. 1 milliampere is, therefore, 1 mA.
• micro- is the prefix used to denote 1 one-millionth of a quantity. A microvolt, for example, is 1 one-millionth of a volt, or 0.000001 V. Often, you will see the Greek letter mu, or μ, used to denote the prefix micro-. 1 microvolt is, therefore, 1 μV.
• pico- is the prefix used to denote 1 one-trillionth of a quantity. A picovolt is 1 one-trillionth of a volt, or 0.000001 μV.
• kilo- is the prefix used to denote 1 thousand of a quantity. A kilovolt, for example, is 1000 volts. Often, the letter k is used instead of the prefix kilo-. 1 kilovolt is, therefore, 1 kV.
• mega- is the prefix used to denote 1 million of a quantity. A megahertz, for example, is 1 million Hertz. Often, the letter M is used instead of the prefix mega-. 1 megahertz is, therefore, 1 MHz.
• giga – is the prefix used to denote one billion of a quantity. One gigahertz, or 1 GHz, for example is 1 billion Hertz.

Here are some examples:

T5B01
How many milliamperes is 1.5 amperes?
A. 15 milliamperes
B. 150 milliamperes
C. 1500 milliamperes
D. 15,000 milliamperes

To convert amperes to milliamperes, you multiply by 1,000.

T5B02
Which is equal to 1,500,000 hertz?
A. 1500 kHz
B. 1500 MHz
C. 15 GHz
D. 150 kHz

To convert from hertz (Hz) to kHz, you divide by 1,000.

T5B03
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

T5B04
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

To convert from kilovolts to volts, you multiply by 1,000. To convert from microvolts to volts, you divide by one million.

T5B05
Which is equal to 500 milliwatts?
A. 0.02 watts
B. 0.5 watts
C. 5 watts
D. 50 watts

To convert from milliwatts to watts, you divide by 1,000. 500 / 1000 = ½ or 0.5.

T5B08
Which is equal to 1,000,000 picofarads?
A. 0.001 microfarads
B. 1 microfarad
C. 1000 microfarads
D. 1,000,000,000 microfarad

The farad is the unit of capacitance. There are 1 million picofarads in a microfarad.

T5B06
Which is equal to 3000 milliamperes?
A. 0.003 amperes
B. 0.3 amperes
C. 3,000,000 amperes
D. 3 amperes

There are a thousand milliamperes in an ampere, so to convert from milliamperes to amperes, you divide by 1,000.

T5C13
What is the abbreviation for kilohertz?
A. KHZ
B. khz
C. khZ
D. kHz

1 kHz is 1,000 Hz or 1,000 cycles per second. Note that the “H” in Hz is capitalized.

T5B07
Which is equal to 3.525 MHz?
A. 0.003525 kHz
B. 35.25 kHz
C. 3525 kHz
D. 3,525,000 kHz

T5B12
Which is equal to 28400 kHz?
A. 28.400 kHz
B. 2.800 MHz
C. 284.00 MHz
D. 28.400 MHz

T5B13
Which is equal to 2425 MHz?
A. 0.002425 GHz
B. 24.25 GHz
C. 2.425 GHz
D. 2425 GHz

To convert from MHz to kHz, you multiply by 1,000. To convert from kHz to MHz, or to convert from MHz to GHz, you divide by 1,000.

Decibels

When dealing with ratios—especially power ratios—we often use decibels (dB). The reason for this is that the decibel scale is a logarithmic scale, meaning that we can talk about large ratios with relatively small numbers. When the value is positive, it means that there is a power increase. When the value is negative, it means that there is a power decrease.

At this point, you don’t need to know the formula used to calculate the ratio in dB, but you need to know the ratios represented by the values 3 dB, 6 dB, and 10 dB.

T5B09
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

3 dB corresponds to a ratio of 2 to 1, and because going from 5 watts to 10 watts doubles the power, we can also say that there is a gain of 3 dB.

T5B10
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

6 dB corresponds to a ratio of 4 to 1, and a decrease in power from 12 watts to 3 watts is a ratio of 4 to 1. Because this is a power decrease, the value in dB is negative.

T5B11
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

Increasing the power from 20 watts to 200 watts is a ratio of 10 to 1, and 10 dB corresponds to a ratio of 10 to 1.