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Technician Course, Module 5: Inside the Radio
Covers NCVEC 2026-2030 Technician Pool, Subelement T7 (Practical Circuits). Four questions on your exam come from this material.
A neighbor knocks on Ray's door holding a portable radio. "Every time you talk on yours, mine goes crazy."
Ray does not apologize and he does not panic. He invites the neighbor in, pours coffee, and starts asking questions. By the end of this module you will understand exactly what he checked, in what order, and why he was smiling the whole time.
5.1The Building Blocks of a Radio
First, the vocabulary of the radio itself.
A transceiver is a transmitter and receiver combined in one box, which is what nearly every ham radio sold today is. Inside it, a handful of circuit blocks do the work:
- An oscillator generates a signal at a specific frequency. It is the radio's heartbeat.
- The VFO (Variable Frequency Oscillator) is the oscillator you control: it sets the receive and transmit frequency. Spin the big knob and you are steering the VFO.
- A mixer converts a signal from one frequency to another. Receivers use mixers to shift incoming signals to frequencies that are easier to filter and amplify.
- Modulation is combining speech (or data) with an RF carrier signal. The microphone by itself makes audio; modulation is how that audio rides the radio wave.
- The PTT (Push-To-Talk) input switches the transceiver from receive to transmit when grounded. That is all the button does: it grounds a wire.
Two words describe how good a receiver is, and they are not the same thing:
- Sensitivity is the ability to detect the presence of a signal. A sensitive receiver hears weak stations.
- Selectivity is the ability to discriminate between multiple signals. A selective receiver hears only the station you want, even with a loud one next door.
Beyond the transceiver, two accessories extend it. An RF power amplifier added to the output increases transmitted power. Some VHF amplifiers have a switch marked SSB or CW-FM, and its purpose is to set the amplifier for proper operation in the selected mode. A transverter converts the RF input and output of a transceiver to another band entirely, which is how hams get on microwave bands using an HF radio as the engine.
Knowledge Check 5.1
Tap an answer. In your own words first, then check yourself.
1. Which receiver quality lets you copy a weak, distant station?
2. What does the mixer stage in a receiver do?
3. What happens electrically when you press the PTT button?
T7A the easy way: all 11 questions, with the right answer
Every pool question in this group. Read the answer, let the tip make it stick.
T7A01 Which term describes the ability of a receiver to detect the presence of a signal?
Answer Sensitivity
Tip Sensitivity is how faint a signal the receiver can still pick out, so a sensitive radio hears the weak ones.
T7A02 What is a transceiver?
Answer A device that combines a receiver and transmitter
Tip Transceiver is transmitter plus receiver in one box, and the word itself is the two mashed together.
T7A03 Which of the following is used to convert a signal from one frequency to another?
Answer Mixer
Tip A mixer is the frequency changer, it takes one frequency in and shifts it to another.
T7A04 Which term describes the ability of a receiver to discriminate between multiple signals?
Answer Selectivity
Tip Selectivity is the receiver separating one signal from its crowded neighbors, so it selects the one you want.
T7A05 What is the name of a circuit that generates a signal at a specific frequency?
Answer Oscillator
Tip An oscillator makes a steady signal at one frequency, it is the radio's built in tone generator.
T7A06 What device converts the RF input and output of a transceiver to another band?
Answer Transverter
Tip A transverter moves your whole radio to a new band by shifting its RF in and out.
T7A07 What is the function of a transceiver’s PTT input?
Answer Switches transceiver from receive to transmit when grounded
Tip PTT means push to talk, and grounding that line flips the radio from listen to transmit.
T7A08 Which of the following describes combining speech with an RF carrier signal?
Answer Modulation
Tip Modulation is putting your voice onto the RF carrier, that is how speech rides out on the signal.
T7A09 What is the function of the switch which selects either SSB or CW-FM on some VHF power amplifiers?
Answer Set the amplifier for proper operation in the selected mode
Tip That mode switch sets the amplifier up correctly for the mode you picked, SSB or CW-FM.
T7A10 What can be added to the output of a transceiver to increase the transmitted output power?
Answer An RF power amplifier
Tip To push more watts out the antenna, add an RF power amplifier after the transceiver.
T7A11 What is the function of the Variable Frequency Oscillator (VFO) circuit in a transceiver?
Answer Set the receive and transmit frequency
Tip The VFO is the tuning dial, it sets both where you receive and where you transmit.
5.2When Radios Fight
Back to Ray's neighbor. Interference between a ham station and consumer electronics almost always comes down to a short list of causes, and radio frequency interference in general can be caused by fundamental overload, harmonics, or spurious emissions. All of the above, as the exam likes to say.
Fundamental overload is the big one for neighbor problems: the consumer receiver is simply unable to reject a strong signal that is outside its own band. Nothing is wrong with your transmitter. The cure lives at the affected receiver: block the amateur signal with a filter at the antenna input of the receiver being interfered with.
Ray's checklist when a neighbor reports interference, and the exam agrees with every step:
- Make sure your own station is functioning properly, and confirm it does not interfere with your own radio or TV tuned to the same channels.
- If something in the neighbor's home is interfering with your station, work with the neighbor to identify the offending device, politely share that FCC rules prohibit devices that cause interference, and keep your own station up to the standards of good amateur practice. All of those together.
- For non-fiber cable TV interference, the first step is unglamorous: be sure all the TV feed line coax connectors are installed properly. Loose F-connectors cause most of it.
Interference also flows the other direction. A nearby commercial FM broadcast station tearing up your 2-meter receiver is fixed with a band-reject filter that notches out the broadcast band.
Then there are problems that are genuinely yours:
- Told you are over-deviating on FM? Your voice is swinging the signal too wide. The fix is free: talk farther away from the microphone.
- Low RF output from a solid-state radio is commonly caused by high SWR, because the radio protects itself (more on that in the next section).
- Reports that your FM audio is distorted or unintelligible can mean your transmitter is slightly off frequency, you are speaking too loudly or too close to the mic, or you are simply in a bad location. Any of them.
- RF feedback, your own transmitted signal getting back into your microphone audio and distorting your voice, is cured by adding a clip-on ferrite choke to the microphone cable.
The theme: diagnose before blaming, and put the fix where the problem actually is.
Knowledge Check 5.2
Tap an answer. In your own words first, then check yourself.
1. Your neighbor's stereo plays your voice whenever you transmit, even though your signal is clean. What is happening?
2. The repeater tells you your FM signal is over-deviating. The simplest fix is:
3. Your transmitted audio is distorted, and clipping a ferrite choke onto the microphone cable fixes it. What was the problem?
T7B the easy way: all 11 questions, with the right answer
Every pool question in this group. Read the answer, let the tip make it stick.
T7B01 What can you do if you are told your FM handheld or mobile transceiver is over-deviating?
Answer Talk farther away from the microphone
Tip Over-deviating on FM usually means you are too loud, so back off and talk farther from the mic.
T7B02 What would cause a broadcast AM or FM radio to receive an amateur radio transmission unintentionally?
Answer The receiver is unable to reject strong signals outside the AM or FM band
Tip If a broadcast set grabs your ham signal, the fault is the receiver failing to reject strong out of band signals.
T7B03 Which of the following can cause radio frequency interference?
Answer All these choices are correct
Tip On what causes RFI, all the listed choices qualify, so pick all these choices are correct.
T7B04 Which of the following might be the cause of low RF power output from a solid-state transceiver?
Answer High SWR
Tip Low power out of a solid-state rig often points to high SWR, the radio is folding back to protect itself.
T7B05 Which of the following might reduce interference by an amateur station to a non-amateur over-the-air radio receiver?
Answer Block the amateur signal with a filter at the antenna input of the affected receiver
Tip Cure interference at the victim by putting a filter on the affected receiver's antenna input to block your signal.
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?
Answer 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
Tip If a neighbor reports interference, first confirm your own station is clean and does not bother your own TV on that channel.
T7B07 Which of the following can reduce interference to a 2-meter band transceiver from a nearby commercial FM station?
Answer Installing a band-reject filter
Tip A strong local FM broadcaster swamping 2 meters calls for a band-reject filter to notch it out.
T7B08 What should you do if something in a neighbor’s home is causing harmful interference to your amateur station?
Answer All these choices are correct
Tip When the trouble comes from a neighbor's equipment, all the listed steps are appropriate, so choose all these choices are correct.
T7B09 What should be the first step to resolve non-fiber optic cable TV interference caused by your amateur radio transmission?
Answer Be sure all TV feed line coaxial connectors are installed properly
Tip For cable TV interference, start simple by checking that every coax connector is tight and properly installed.
T7B10 What might be a problem if you receive a report that your audio signal through an FM repeater is distorted or unintelligible?
Answer All these choices are correct
Tip Distorted audio through a repeater can come from several causes, so the answer is all these choices are correct.
T7B11 Which of the following can eliminate distorted voice transmissions?
Answer Adding a clip-on ferrite “choke” to the microphone cable to prevent the transmitted signal from feeding back into the transmitter
Tip A clip-on ferrite choke on the mic cable stops RF feedback into the transmitter and clears distorted audio.
5.3Feed Line Health and the Dummy Load
Ray hands you a heavy cylinder with one connector and no antenna. "Fifty ohms of pure resistor on a heat sink. Best test instrument in the shack."
That is a dummy load: a 50-ohm non-inductive resistor mounted on a heat sink, and its primary purpose is to prevent transmitting signals over the air while making tests. The radio sees a perfect match, your tests bother nobody, and any problem you observe is in the radio, not the antenna. Testing into the dummy load is step one of splitting every transmit problem in half.
Now the number that rules the antenna system: SWR (standing wave ratio), a measure of how well the load is matched to the transmission line. The scores:
- 1:1 is a perfect match between antenna system and feed line.
- 4:1 means an impedance mismatch. Power is being reflected back down the line instead of leaving.
Why care? Most solid-state transmitters reduce output power as SWR climbs, specifically to protect the RF output amplifier transistors. That fold-back is the "high SWR causes low output" answer from the last section, now explained.
Measuring it: an SWR meter or a directional wattmeter in the feed line can determine SWR, and an antenna analyzer is the tool for finding whether an antenna is resonant at the desired frequency without transmitting at all.
Feed line failures come from a rogues' gallery you can memorize:
- Moisture contamination is the classic coax killer.
- Ultraviolet light damages the outer jacket, which then lets water enter the cable. That is why the jacket must be UV resistant.
- Sources of loss in a coax run include water in the connectors, high SWR, and multiple connectors in the line. All of them.
- Whatever power the feed line loses is converted into heat. It does not radiate, it does not come back, it just warms the cable.
- Erratic SWR changes point at a loose connection in the antenna or feed line.
Choosing coax: RG-213 has less loss than skinny RG-58 at any given frequency, foam-dielectric cable has less loss per foot than solid-dielectric, air-insulated hardline is the lowest-loss feed line of all, and loss always increases as frequency increases. Fifty ohms is the standard impedance, and the reason coax dominates amateur stations is simple: it is easy to use and requires few special installation considerations.
Knowledge Check 5.3
Tap an answer. In your own words first, then check yourself.
1. What is the primary purpose of a dummy load?
2. Your SWR reading jumps around erratically during transmit. The most likely cause is:
3. Where does the power lost in a feed line go?
T7C the easy way: all 11 questions, with the right answer
Every pool question in this group. Read the answer, let the tip make it stick.
T7C01 What is the primary purpose of a dummy load?
Answer To prevent transmitting signals over the air when making tests
Tip A dummy load lets you test into a fake 50-ohm antenna so you do not put a signal on the air.
T7C02 Which of the following is used to determine if an antenna is resonant at the desired operating frequency?
Answer An antenna analyzer
Tip To check if an antenna is resonant where you want, reach for an antenna analyzer.
T7C03 What does a typical RF dummy load consist of?
Answer A 50-ohm non-inductive resistor mounted on a heat sink
Tip A dummy load is just a 50-ohm non-inductive resistor on a heat sink, soaking up power as heat.
T7C04 What reading on an SWR meter indicates a perfect impedance match between the antenna and the feed line?
Answer 1:1
Tip A 1:1 reading on the SWR meter is the perfect match, antenna and feed line agree completely.
T7C05 Why do most solid-state transmitters reduce output power as SWR increases beyond a certain level?
Answer To protect the RF output amplifier transistors
Tip Solid-state rigs cut power as SWR climbs to protect the output transistors from reflected power.
T7C06 What does an SWR reading of 4:1 indicate?
Answer Impedance mismatch
Tip A 4:1 SWR reading simply means the impedances do not match well.
T7C07 What happens to power lost in a feed line?
Answer It is converted into heat
Tip Power that does not make it down the feed line is lost as heat in the cable.
T7C08 Which instrument can be used to determine SWR?
Answer Directional wattmeter
Tip An SWR reading comes right off a directional wattmeter by comparing forward and reflected power.
T7C09 Which of the following causes failure of coaxial cables?
Answer Moisture contamination
Tip Coax fails when moisture gets inside, so keep water out of your cable.
T7C10 Why should the outer jacket of coaxial cable be resistant to ultraviolet light?
Answer Ultraviolet light can damage the jacket and allow water to enter the cable
Tip A UV-resistant jacket matters because sunlight cracks the jacket and lets water into the coax.
T7C11 What is an advantage of foam-dielectric versus solid-dielectric coaxial cable?
Answer It has less loss per foot
Tip Foam-dielectric coax beats solid for loss, it gives you less loss per foot.
5.4The Multimeter and the Iron
Two skills separate hams who fix things from hams who ship things back: measuring and soldering.
The multimeter combines the three basic instruments, and each has its own connection rule:
- A voltmeter measures electric potential, and it connects in parallel with the component, across it, while the circuit runs.
- An ammeter measures current, and it connects in series, so the current flows through the meter. You have to break the circuit to insert it.
- An ohmmeter measures resistance by applying a small current and measuring the resulting voltage. Two safety rules come with it: the circuit must be unpowered before you measure resistance, and attempting to measure voltage while the meter is set to resistance can damage the meter.
One classic reading worth knowing: connect an ohmmeter across a large discharged capacitor and you will see the resistance increase with time as the meter's own current charges it. That rising reading is a healthy capacitor saying hello.
Then the iron. Soldering rules the exam checks:
- Never use acid-core solder for electronics. Acid flux is for plumbing, and it will corrode your circuit from the inside. Rosin-core is the electronics standard.
- A cold solder joint, made without enough heat, has a characteristic rough or lumpy surface instead of a smooth bright fillet. Cold joints work today and fail on the mountaintop.
Knowledge Check 5.4
Tap an answer. In your own words first, then check yourself.
1. To measure the current a radio draws, the meter must be connected:
2. Before measuring resistance in a circuit, you must:
3. A solder joint with a rough, lumpy surface indicates:
T7D the easy way: all 11 questions, with the right answer
Every pool question in this group. Read the answer, let the tip make it stick.
T7D01 Which instrument would you use to measure electric potential?
Answer A voltmeter
Tip Electric potential means voltage, so you measure it with a voltmeter.
T7D02 How is a voltmeter connected to a component to measure applied voltage?
Answer In parallel
Tip A voltmeter goes across the component, wired in parallel to read the voltage on it.
T7D03 When configured to measure current, how is a multimeter connected to a component?
Answer In series
Tip To read current, break the circuit and put the meter in series so the current flows through it.
T7D04 Which instrument is used to measure electric current?
Answer An ammeter
Tip Current is measured with an ammeter, amps and ammeter share the name.
T7D05 How does an ohmmeter measure the resistance of a circuit or component?
Answer By applying a small current and measuring the resulting voltage
Tip An ohmmeter pushes a tiny current through the part and reads the voltage to work out resistance.
T7D06 Which of the following can damage a multimeter?
Answer Attempting to measure voltage when using the resistance setting
Tip Putting meter probes on live voltage while set to resistance can wreck a multimeter.
T7D07 Which of the following measurements are made using a multimeter?
Answer Voltage and resistance
Tip A multimeter is many meters in one, and among its jobs are voltage and resistance.
T7D08 Which of the following types of solder should not be used for radio and electronic applications?
Answer Acid-core solder
Tip Never use acid-core solder on electronics, the acid corrodes connections, save it for plumbing.
T7D09 What is the characteristic appearance of a cold tin-lead solder joint?
Answer A rough or lumpy surface
Tip A cold solder joint looks rough and lumpy instead of smooth and shiny.
T7D10 What reading indicates that an ohmmeter is connected across a large, discharged capacitor?
Answer Increasing resistance with time
Tip An ohmmeter on a big discharged capacitor shows resistance rising as the cap charges from the meter.
T7D11 Which of the following precautions should be taken when measuring in-circuit resistance with an ohmmeter?
Answer Ensure that the circuit is not powered
Tip Before measuring resistance in a circuit, kill the power, an ohmmeter must see a dead circuit.
Review: every Exam Anchor from this module
T7A Transceiver: combined receiver and transmitter. Oscillator: generates a signal at a specific frequency. VFO: sets receive and transmit frequency. Mixer: converts a signal from one frequency to another. Modulation: combining speech with an RF carrier. PTT: switches to transmit when grounded. Sensitivity: detecting the presence of a signal. Selectivity: discriminating between signals. RF power amplifier: increases output power. The SSB/CW-FM switch on a VHF amplifier sets it for proper operation in that mode. Transverter: converts a transceiver's RF input and output to another band.
T7B RFI causes: fundamental overload, harmonics, spurious emissions (all of these). Broadcast receiver picking up your transmission: fundamental overload, cured by a filter at the affected receiver's antenna input. Neighbor complains: first verify your station is clean, including against your own TV and radio. Neighbor's device interferes with you: work together, cite the rules politely, keep your station clean (all of these). Cable TV interference: check the coax connectors first. Commercial FM into your 2-meter rig: band-reject filter. Over-deviating: talk farther from the mic. Low output from a solid-state rig: high SWR. Distorted FM audio: off frequency, too loud or too close, or bad location (all of these). Distortion from RF feedback: ferrite choke on the mic cable.
T7C Dummy load: 50-ohm non-inductive resistor on a heat sink; prevents transmitting over the air during tests. SWR 1:1 = perfect match; 4:1 = impedance mismatch. Solid-state rigs reduce power at high SWR to protect the output transistors. SWR is measured with a directional wattmeter; resonance is found with an antenna analyzer. Coax fails from moisture contamination; UV damages the jacket and lets water in. Feed line loss sources: water in connectors, high SWR, multiple connectors (all of these). Lost feed line power becomes heat. Erratic SWR = loose connection.
T7D Voltmeter: measures potential, connects in parallel. Ammeter: measures current, connects in series. Ohmmeter: applies a small current and measures voltage; circuit must be unpowered; measuring voltage on the resistance setting can damage the meter. Ohmmeter across a discharged capacitor: resistance increases with time. Never use acid-core solder for electronics. Cold solder joint: rough or lumpy surface.
Before you move on
You now know the blocks inside a transceiver, the short list of causes behind almost every interference complaint, the health signs of a feed line, and how to hold a multimeter and an iron without hurting anything. Ray's neighbor, by the way, had a twenty-year-old stereo with no front-end filtering: fundamental overload, cured with a ten-dollar filter on its antenna wire, and the two of them are friends now.
Module 6 is where the signals themselves get interesting: FM versus SSB, bandwidth, digital modes, and how to talk through a satellite.
© 2026 Anthony Pelfanio, K4DIA. All rights reserved.