T7 — Practical Circuits
4 exam questions · 4 groups · 43 questions in pool
Equipment at the block-diagram level and the everyday troubleshooting that keeps a station on the air: what receivers, transmitters, and amplifiers do; diagnosing interference and RF feedback; measuring SWR and caring for feed lines; and using basic test meters and soldering properly. (T7D has 10 questions — T7D05 was withdrawn in the errata.) No FCC citations.
T7A — Station Equipment; Basic Radio Concepts
11 questions
What this group tests: the building blocks of a radio and the vocabulary for what each does.
Foundational concepts
A transceiver is simply a receiver and transmitter combined in one box. Two key receiver qualities: sensitivity is the ability to detect a weak signal, and selectivity is the ability to discriminate between signals close in frequency.
Inside, a few named circuits do specific jobs. A mixer converts a signal from one frequency to another. An oscillator generates a signal at a specific frequency. Modulation is the act of combining speech (or data) with an RF carrier. A transverter shifts a transceiver’s RF input/output to another band.
For boosting signals: an RF power amplifier increases transmitted output power and sits after the transceiver, while an RF preamplifier boosts weak received signals and is installed between the antenna and the receiver. A VHF amplifier’s SSB/CW–FM switch configures it for proper operation in the selected mode. Finally, the PTT (push-to- talk) input switches the radio from receive to transmit when grounded.
Key facts to retain
- Transceiver = RX + TX. Sensitivity = detect weak; selectivity = separate signals.
- Mixer changes frequency; oscillator generates a frequency; modulation = speech onto a carrier; transverter = move to another band.
- Power amp boosts TX output; preamp goes between antenna and receiver; PTT keys TX when grounded.
External reference anchors
- NCVEC syllabus: T7A — Station equipment; basic radio circuit concepts (sensitivity, selectivity, mixers, oscillators, PTT, modulation)
Per-question map
| Q | Asks for | Resolved by |
|---|---|---|
| T7A01 | Detect presence of a signal | Sensitivity |
| T7A02 | What a transceiver is | Combines RX and TX |
| T7A03 | Convert one frequency to another | Mixer |
| T7A04 | Discriminate between signals | Selectivity |
| T7A05 | Generates a specific frequency | Oscillator |
| T7A06 | Converts RF to another band | Transverter |
| T7A07 | PTT input function | RX→TX when grounded |
| T7A08 | Speech + RF carrier | Modulation |
| T7A09 | VHF amp SSB/CW-FM switch | Sets amp for the mode |
| T7A10 | Increases transmit power | RF power amplifier |
| T7A11 | Where a preamp goes | Between antenna and receiver |
T7B — Interference and RF Feedback
11 questions
What this group tests: the symptoms, causes, and cures of overload, distortion, and interference between your station and consumer electronics.
Foundational concepts
Most consumer-electronics interference is fundamental overload: a nearby strong amateur signal swamps a receiver that can’t reject signals outside its own band. The cure is to filter at the affected receiver’s antenna input (a band-reject/high-pass filter there), not at your transmitter — the problem is the victim’s front end. A band-reject filter likewise tames a VHF transceiver overloaded by a strong commercial FM station. RFI has many possible causes — “all of these.”
A few specific fixes: RF current on a microphone cable shield causing distortion is cured with a ferrite choke. The first step for cable-TV interference is to make sure all coax connectors are properly installed. If a neighbor reports interference, your first responsibility is to verify your own station is operating properly and isn’t interfering with your own TV on the same channel. If something in the neighbor’s home is interfering with you, there are several reasonable steps — “all of these.”
RF feedback is RF getting back into your transmitter’s audio stages; its hallmark symptom is garbled, distorted, or unintelligible transmitted voice. Over-deviation on an FM handheld (talking too loud/close) is cured by talking farther from the mic, and a distorted repeater signal can have several causes — “all of these.”
Key facts to retain
- Fundamental overload = victim receiver can’t reject your strong signal → filter at the victim’s antenna input.
- Ferrite choke cures RF on a mic cable shield; check coax connectors first for CATV interference.
- Neighbor complains → verify your station is clean first.
- RF feedback → garbled/distorted transmitted audio; over-deviation → back off the mic.
External reference anchors
- NCVEC syllabus: T7B — Symptoms, causes, cures of transmitter/receiver problems: overload, distortion, interference, RF feedback
Per-question map
| Q | Asks for | Resolved by |
|---|---|---|
| T7B01 | Over-deviating handheld | Talk farther from the mic |
| T7B02 | Broadcast radio hears amateur | Can’t reject strong out-of-band signals |
| T7B03 | Causes of RFI | All these choices |
| T7B04 | RF on mic cable shield | Ferrite choke |
| T7B05 | Cure fundamental overload | Filter at victim’s antenna input |
| T7B06 | Neighbor reports interference | Verify your own station is proper |
| T7B07 | Overload by commercial FM | Band-reject filter |
| T7B08 | Neighbor’s home interferes with you | All these choices |
| T7B09 | First step, CATV interference | Check coax connectors |
| T7B10 | Distorted repeater audio | All these choices |
| T7B11 | RF feedback symptom | Garbled/distorted voice |
T7C — Antenna and Feed Line Measurements; SWR; Coax; Dummy Loads
11 questions
What this group tests: measuring SWR and why it matters, feed-line losses and failures, coax characteristics, and the dummy load.
Foundational concepts
SWR (standing wave ratio) measures how well the antenna’s impedance matches the feed line. A 1:1 reading is a perfect match; a reading like 4:1 indicates an impedance mismatch. SWR is read with an SWR meter or a directional wattmeter. High SWR matters because most solid-state transmitters reduce power as SWR rises to protect the output transistors. Whatever power is lost in a feed line turns into heat. To find whether an antenna is resonant at your frequency, use an antenna analyzer.
A dummy load is a non-inductive resistor on a heat sink that lets you test a transmitter without radiating a signal over the air. Coax care: moisture is a prime cause of cable failure, so the jacket must resist UV (UV degrades the jacket and lets water in). Air-core coax has lower loss but requires special techniques to keep moisture out compared with foam/solid dielectric.
Key facts to retain
- SWR 1:1 = perfect match; 4:1 = mismatch. Read with SWR meter / directional wattmeter.
- High SWR → solid-state rigs fold back power to protect output transistors.
- Feed-line loss becomes heat; antenna analyzer checks resonance.
- Dummy load = non-inductive resistor + heat sink; lets you test without transmitting.
- Moisture kills coax; jacket must resist UV.
External reference anchors
- NCVEC syllabus: T7C — Antenna/transmission-line measurements; SWR; coax characteristics; dummy loads
Per-question map
| Q | Asks for | Resolved by |
|---|---|---|
| T7C01 | Purpose of a dummy load | Test without transmitting on air |
| T7C02 | Check antenna resonance | Antenna analyzer |
| T7C03 | What a dummy load is | Non-inductive resistor on heat sink |
| T7C04 | Perfect-match SWR | 1:1 |
| T7C05 | Why rigs reduce power at high SWR | Protect output transistors |
| T7C06 | SWR 4:1 means | Impedance mismatch |
| T7C07 | Fate of feed-line loss | Converted to heat |
| T7C08 | Instrument to determine SWR | Directional wattmeter |
| T7C09 | Cause of coax failure | Moisture contamination |
| T7C10 | Why UV-resistant jacket | UV lets water enter |
| T7C11 | Air-core coax disadvantage | Needs moisture-prevention techniques |
T7D — Test Instruments; Soldering
10 questions
What this group tests: how to connect and use a voltmeter, ammeter, and ohmmeter safely, and what good vs. bad soldering looks like.
Foundational concepts
How a meter connects depends on what it reads. A voltmeter measures potential and connects in parallel (across) the component. An ammeter measures current and connects in series (in line) so the current flows through it. A multimeter measures voltage and resistance (and current). The dangerous mistake: trying to measure voltage while set to the resistance (ohms) range can damage the meter. When measuring in-circuit resistance, always make sure the circuit is unpowered first. A clue about component behavior: an ohmmeter across a large discharged capacitor shows resistance increasing over time as the cap charges from the meter.
For soldering: never use acid-core solder on electronics (it’s for plumbing and corrodes connections) — use rosin-core. A cold solder joint (joint that moved or wasn’t hot enough) has a rough, lumpy, dull appearance instead of a smooth shiny one.
Key facts to retain
- Voltmeter → parallel; ammeter → series. Multimeter does voltage + resistance.
- Measuring volts on the ohms setting damages the meter; de-power circuits before measuring resistance.
- Acid-core solder is wrong for electronics; cold joint looks rough/lumpy.
External reference anchors
- NCVEC syllabus: T7D — Using basic test instruments (voltmeter, ammeter, ohmmeter); Soldering
Per-question map
| Q | Asks for | Resolved by |
|---|---|---|
| T7D01 | Measure electric potential | A voltmeter |
| T7D02 | How to connect a voltmeter | In parallel |
| T7D03 | Multimeter to measure current | In series |
| T7D04 | Measure electric current | An ammeter |
| T7D06 | Can damage a multimeter | Volts on the resistance setting |
| T7D07 | Multimeter measurements | Voltage and resistance |
| T7D08 | Solder not for electronics | Acid-core solder |
| T7D09 | Cold solder joint look | Rough or lumpy surface |
| T7D10 | Ohmmeter on discharged cap | Increasing resistance with time |
| T7D11 | In-circuit resistance precaution | Ensure circuit is unpowered |