CA_BASIC
Basic - Basic radio theory
Basic radio theory follows the B-003 section of the Canadian question bank.
199
Questions
7
Sibling Topics
- Pool
- Basic
- Questions
- 199
- Topic
- Basic radio theory
- Region
- CA
Review by section order to build the topic framework first.
For regulatory and safety questions, prefer compliant and conservative actions.
For calculations, check units, multipliers, and approximations.
Topic Study Guide
This topic covers the core radio theory and safety regulations for the Canadian Amateur Basic exam (B-003). Key areas include transmitter and receiver principles, modulation characteristics, power supply basics, and critical electrical and RF safety guidelines.
High-Yield Checks
- Superheterodyne principles: Focus on how the mixer converts signals to a fixed intermediate frequency, and how the IF filter provides the receiver's main selectivity.
- SSB and modulation characteristics: Understand that ALC limits audio peaks to prevent overdrive, while a speech processor increases average power, not Peak Envelope Power (PEP).
- Equipment connection and filtering: Low-pass filters must be installed as close to the transceiver output as possible; sound card interfaces handle audio frequency coupling.
- Safety protocols: Remember the AC green wire goes to the chassis, vehicle positive leads need fuses to prevent fires, and the first step in high-voltage rescue is always turning off the power.
Trap Patterns
- Confusing ALC and AGC: It is easy to mix up Automatic Level Control (ALC) used in transmitters with Automatic Gain Control (AGC) used in receivers.
- Misunderstanding speech processor side effects: Assuming over-processing only changes volume, ignoring that it causes audio distortion and splatter interference on adjacent frequencies.
- Local Oscillator (LO) calculation errors: Losing points when calculating LO frequencies by adding/subtracting the IF incorrectly or misaligning decimals when converting kHz to MHz.
- Instinctive safety errors: In shock rescue questions, instinctively choosing to 'drag the person away' instead of cutting power first; or confusing a 'positioning waist belt' with proper 'fall arrest equipment'.
Review Steps
- Map the signal flow: Build a clear framework of how signals travel inside transmitters and receivers, from the microphone to the speech amplifier, mixer, and filters.
- Compare modulation modes: Clarify the core differences between AM, FM, SSB, and CW, such as why FM isn't used below 28 MHz (bandwidth limits) and why FT8 is efficient (narrow bandwidth).
- Practice calculations specifically: For Local Oscillator (LO) questions, write down the formula (Operating Freq ± IF) on scratch paper and double-check unit conversions.
- Reinforce safety baseline thinking: Group and review all electrical, RF exposure, and tower safety questions, always selecting the most conservative, life-protecting option.
Quick Checks
- In a superheterodyne receiver, which component converts the received frequency to a fixed intermediate frequency?
- To be most effective at suppressing harmonics, where in the system should a low-pass filter be installed?
- Using a speech processor in an SSB transmitter increases which type of power?
- What should be your very first action if you discover someone being shocked by high voltage?
Questions in This Topic
Choose Practice ModeB-003-001-001To be most effective, where should a low-pass filter be connected in an HF station without an external power amplifier?B-003-001-002In an HF station that includes an external RF power amplifier, where should a low-pass filter be located?B-003-001-003Why do modern HF transmitters have a built-in low-pass filter in their RF output circuits?B-003-001-004Which component in an HF station is used to determine if the antenna system impedance is matched to the transmitter?B-003-001-005What is the purpose of the antenna switch in an HF station?B-003-001-006In an HF station, what device might allow the use of an antenna on a band it was not designed for?B-003-001-007In an HF station, which component is designed to dissipate RF energy and prevent radiation?B-003-001-008In an HF station, right after which component is the SWR meter inserted?B-003-001-009When using an HF transmitter with a solid-state final amplifier, which station component may need to be adjusted when changing frequency?B-003-002-001What does the microphone produce in an FM transmitter?B-003-002-002The microphone of an FM transmitter:B-003-002-003An FM transmitter's modulator:B-003-002-004How is the oscillator in the FM transmitter different from oscillators in AM, CW, and SSB transmitters?B-003-002-005In an FM transmitter, the frequency multiplier:B-003-002-006In an FM transmitter, which stage produces a useful harmonic?B-003-002-007In an FM transmitter, which stage draws the most electric power?B-003-003-001In a superheterodyne receiver, which stage is called the front-end?B-003-003-002In a VHF superheterodyne receiver, which stage must be designed to produce very little noise?B-003-003-003In a superheterodyne receiver, which stage allows detection to function at a single frequency regardless of the received frequency?B-003-003-004In a superheterodyne receiver, which stage sets the received frequency?B-003-003-005In a superheterodyne receiver, which stage rejects signals on adjacent channels?B-003-003-006In a superheterodyne receiver, which stage provides the final signal power to drive the detector?B-003-003-007In an FM receiver, what is the purpose of the limiter?B-003-003-008In an FM receiver, what is the purpose of the discriminator?B-003-003-009In a receiver, which stage is controlled by the volume control?B-003-003-010In an FM receiver, which stage includes a squelch circuit?B-003-004-001In a basic CW transmitter, the output from the oscillator is:B-003-004-002In a basic CW transmitter, what type of electricity directly powers each stage?B-003-004-003In a basic CW transmitter, why is the oscillator followed by a driver/buffer stage?B-003-004-004In a basic three-stage CW transmitter, what does the key do?B-003-004-005In a basic CW transmitter, what does the power amplifier stage do?B-003-004-006In a basic CW transmitter, what does the key do?B-003-005-001In an SSB/CW receiver, what is the purpose of the antenna?B-003-005-002In an SSB/CW receiver, what is the purpose of the radio frequency (RF) amplifier?B-003-005-003In an SSB/CW receiver, what is the purpose of the mixer?B-003-005-004In an SSB/CW receiver, what is the purpose of the signal generated by the local oscillator?B-003-005-005In an SSB/CW receiver, what is the purpose of the intermediate frequency (IF) filter?B-003-005-006In an SSB/CW receiver, what is the purpose of the intermediate frequency (IF) amplifier?B-003-005-007In an SSB/CW receiver, what is the purpose of the product detector?B-003-005-008In an SSB/CW receiver, what is the purpose of the signal produced by the beat frequency oscillator (BFO)?B-003-005-009In an SSB/CW receiver, what is the purpose of the audio frequency (AF) amplifier?B-003-005-010In an SSB/CW receiver, which stage could include an audio band-pass filter?B-003-006-001In a single-sideband transmitter, what does the fixed RF oscillator do?B-003-006-002In a single-sideband transmitter, why is the speech amplifier needed?B-003-006-003In a typical single-sideband transmitter, what is the purpose of the filter that follows the balanced modulator?B-003-006-004In a typical single-sideband transmitter, at what frequency is the sideband filter tuned?B-003-006-005In a single-sideband transmitter, what is the purpose of the speech amplifier?B-003-006-006In a single-sideband transmitter, which stage transposes the single-sideband signal to the operating frequency?B-003-006-007In a single-sideband transmitter, which stage allows you to adjust the final transmit frequency?B-003-006-008In a single-sideband transmitter, which stage normally includes a circuit providing protection from excessive SWR?B-003-006-009In a single-sideband transmitter, which stage transposes the voice message from the audio spectrum to the radio spectrum?B-003-007-001Which of the following is a function of the sound card interface in a station operating computer-based digital modes?B-003-007-002Which of the following is a function of the sound card interface in a station operating computer-based digital modes?B-003-007-003Which of the following is one function of most sound card interfaces in a station operating computer-based digital modes?B-003-007-004Which of the following is a function of the sound card interface in a station operating computer-based digital modes?B-003-007-005Why are isolation transformers often included in the sound card interface of a station operating computer-based digital modes?B-003-007-006Why are some transceivers capable of operating computer-based digital modes without a separate sound card?B-003-008-001If a linear power supply provides overvoltage protection, where is the voltage monitored?B-003-008-002What is the purpose of the transformer in a linear power supply?B-003-008-003What is the purpose of the rectifier in a linear power supply?B-003-008-004What is the purpose of the filter in a linear power supply?B-003-008-005What is the purpose of the regulator in a linear power supply?B-003-008-006In a linear power supply, which stage typically requires a heat sink?B-003-009-001Which component of a 3-element Yagi antenna is primarily for mechanical support?B-003-009-002In a 3-element Yagi antenna, what is the longest radiating element?B-003-009-003In a 3-element Yagi antenna, which is the shortest radiating element?B-003-009-004In a 3-element Yagi antenna, which element is connected to the transmission line?B-003-010-001Which series of emission modes listed below is in order from the narrowest bandwidth to the widest bandwidth?B-003-010-002The figure in a receiver's specifications which indicates its sensitivity is the:B-003-010-003What are the two signal parameters presented to the user on the waterfall display (spectrogram) of a modern receiver?B-003-010-004What is the function of automatic gain control (AGC) in a receiver?B-003-010-005For which of the following emission modes is it important for the receiver to be tuned accurately (within 100 Hz)?B-003-010-006A superheterodyne receiver has an intermediate frequency (IF) of 455 kHz. The local oscillator runs above the operating frequency. To which frequency should it be tuned to receive a signal on 3.54 MHz?B-003-010-007When receiving a modulated signal, what is the adverse consequence of too narrow a receiver bandwidth?B-003-010-008Apart from sensitivity and selectivity, which of these is the third main indicator of communications receiver performance?B-003-010-009A communications receiver has four filters installed in it, respectively designated as 250 Hz, 500 Hz, 2.4 kHz, and 6 kHz. If you were listening to single sideband, which filter would you utilize?B-003-010-010A communications receiver has four filters installed in it, respectively designated as 250 Hz, 500 Hz, 2.4 kHz and 6 kHz. You are copying a CW transmission and there is a great deal of interference. Which one of the filters would you choose?B-003-010-011When receiving CW, which of these frequency ranges is optimum for a band-pass filter?B-003-011-001What does chirp mean?B-003-011-002What can be done to keep a CW transmitter from chirping?B-003-011-003What is the advantage of using a variable frequency oscillator in a basic CW transmitter?B-003-011-004Which type of transmitter modulation changes the amplitude of an RF wave for the purpose of conveying information?B-003-011-005In what emission mode does the instantaneous amplitude (envelope) of the RF signal vary with the modulating audio?B-003-011-006Morse code is usually transmitted by radio as:B-003-011-007You are transmitting using amplitude modulation. What bandwidth does your signal occupy if the highest frequency of your voice is 3 kHz?B-003-011-008What frequency components are present in the bandwidth of an amplitude modulated signal?B-003-011-009An RF oscillator should be electrically and mechanically stable. This is to ensure that the oscillator does NOT:B-003-011-010The DC power to the final stage of your transmitter is 200 watts and the RF output is 125 watts. What has happened to the rest of the power?B-003-011-011The difference between DC input power and RF output power of a transmitter RF amplifier:B-003-012-001What may happen if an SSB transmitter is operated with the microphone gain set too high?B-003-012-002What may happen if an SSB transmitter is operated with too much speech processing?B-003-012-003What is the term for the average power during one RF cycle, at the crest of the modulation envelope?B-003-012-004What is the usual bandwidth of an amateur radio single-sideband signal?B-003-012-005Why does the power amplifier of the SSB transmitter need to be linear?B-003-012-006What is one advantage of carrier suppression in a double sideband voice transmission?B-003-012-007What does overmodulation do to a single-sideband signal?B-003-012-008How should the microphone gain control be adjusted for voice operation on a single-sideband transmitter?B-003-012-009The purpose of a balanced modulator in an SSB transmitter is to:B-003-012-010Your SSB transmitter is set to operate lower sideband at 7100 kHz. With a single 1000 Hz tone as modulation, at which frequency is RF transmitted?B-003-012-011The automatic level control (ALC) in an SSB transmitter:B-003-013-001What causes the loud noise heard from an FM receiver in the absence of a signal?B-003-013-002You are using an FM repeater configured for 5 kHz deviation, but your transmitter is set to 2.5 kHz deviation. What is the consequence?B-003-013-003What term defines the change in frequency caused by modulation in an FM transmitter?B-003-013-004What kind of emission would your FM transmitter produce if its microphone failed to work?B-003-013-005Why is FM voice best for local VHF/UHF radio communications?B-003-013-006What is the approximate bandwidth of a frequency modulated signal using 5 kHz deviation?B-003-013-007How is a higher level of the modulating signal represented in an FM signal?B-003-013-008What modulation method is most closely related to frequency modulation?B-003-013-009Why isn't FM used as an amateur radio emission mode below 28 MHz?B-003-013-010Several stations report that your FM transmission is loud and distorted, but on frequency. Which of the following is the most probable cause of the distortion?B-003-013-011When more than one signal is present, the FM receiver is likely to demodulate only the strongest signal. What is this behaviour called?B-003-014-001What do many amateur radio operators use to help form good Morse code characters?B-003-014-002How does an electronic keyer help form good Morse code characters?B-003-014-003What do you need to adjust before using a microphone for the first time with a transceiver?B-003-014-004What noise management system analyzes noise and signal characteristics to partially remove noise?B-003-014-005What circuit causes a transmitter to automatically transmit when an operator speaks into its microphone?B-003-014-006What is the reason for using a properly adjusted speech processor with a single-sideband voice transmitter?B-003-014-007If a single-sideband voice transmitter is 100% modulated, how will using a speech processor affect the transmitter's output?B-003-014-008In a receiver, what noise management circuit recognizes high-amplitude short-duration pulses and removes them?B-003-014-009What type of interference is a noise blanker circuit most effective in eliminating?B-003-014-010What is the function of transmit/receive switching in a transceiver?B-003-014-011What type of microphone has internal components similar to a loudspeaker?B-003-015-001Why can a modern digital radio system transmit voice and images, not just data?B-003-015-002What is the fundamental difference between digital and analog data?B-003-015-003What is the function of a digipeater?B-003-015-004What does "network" mean in packet radio?B-003-015-005Why can dozens of FT8 communications occur simultaneously in the space needed for one single-sideband transmission?B-003-015-006Which of these modes can work at the lowest signal-to-noise ratio as measured in a 2500 Hz bandwidth?B-003-015-007When selecting an RTTY transmitting frequency, what minimum frequency separation from a contact in progress should you allow (centre to centre) to minimize interference?B-003-015-008When using a digital mode based on a computer sound card, how can you verify that the transmit audio level is NOT excessive?B-003-015-009What feature of packet radio makes it especially useful for emergency communications?B-003-015-010A digital protocol implements automatic repeat request (ARQ). What does it permit?B-003-015-011With a digital communication mode based on a computer sound card, what is the result of feeding excessive audio into the transmitter?B-003-016-001What approximate voltage does a standard automobile starter battery usually supply?B-003-016-002Which of the following has a positive terminal and a negative terminal?B-003-016-003A battery, that can be repeatedly recharged by supplying it with electrical energy, is known as a:B-003-016-004Which of the following is a source of electromotive force (EMF)?B-003-016-005Why is the NiMH battery often preferred over a conventional alkaline battery?B-003-016-006The voltage at a battery's terminals will drop when it supplies current. What is the cause of the drop?B-003-016-007For portable operation, what is the primary advantage of lithium-based batteries over lead-acid batteries?B-003-016-008Battery capacity is commonly stated as a value of current delivered over a specified period of time. What is the effect of exceeding that specified current?B-003-016-009What voltage and capacity will you achieve by connecting two 12 volts, 20 ampere-hour batteries in parallel?B-003-016-010What voltage and capacity will you achieve by connecting two 12 volts, 20 ampere-hour batteries in series?B-003-016-011A lithium-ion battery should never be:B-003-017-001You construct a simple DC power supply using a transformer, rectifier and filter capacitor. If you use the supply to power a CW transmitter, what problem with signal quality could it cause?B-003-017-002What device converts 120 volts AC to 12 volts DC?B-003-017-003When selecting a 13.8 V DC power supply for a transceiver, what design specification is most important?B-003-017-004Compared to a switching (switch mode) power supply, why may a linear power supply be preferred?B-003-017-005In a mobile installation, why should the fuse in the DC line to the transceiver be located as near to the battery as possible?B-003-017-006Apart from efficiency, what is one advantage of a switching (switch mode) power supply over a linear power supply?