Free ACMA Standard Theory Exam Flashcards

After frequency conversion, the receiver processes the wanted signal at a fixed intermediate frequency. IF amplification and filtering provide useful gain and selectivity before demodulation and audio recovery.

The Standard syllabus says it must be approved by an electricity authority or other relevant authority and carry an approval label. Do not treat unfamiliar mains equipment as safe merely because it powers on.

Treat it as dangerous and have it replaced or repaired by an authorised person. Do not rely on temporary tape repairs or continue using a lead that can expose conductors or create a fire risk.

Excessive volume can damage hearing. Set a safe listening level before extended operation, especially where strong signals or changing audio levels might tempt an operator to turn the volume up.

All can help check frequency, but each has limits in accuracy, stability, signal conditions, and setup. Use the right reference for the required accuracy rather than assuming a counter reading alone proves a transmitter is on frequency.

Voltage is electrical potential difference—the driving pressure. Current is the flow of electric charge. A circuit needs both an applied voltage and a closed path for sustained current flow.

A resistor converts electrical energy to heat. After calculating dissipation with an appropriate power formula, select a component rating with suitable margin so normal operation does not overheat or damage it.

It encodes a resistor's nominal resistance and, where applicable, its tolerance. Read the bands in the correct direction and use the multiplier band before deciding whether a value is suitable in a circuit.

P = EI, P = I²R, and P = E²/R. Select the form that uses the quantities you know, keep units consistent, and distinguish power dissipation from voltage or current alone.

A polarised capacitor is designed for a particular DC polarity. Reversing it can damage its dielectric, create excessive leakage or heating, and in some types lead to venting or rupture.

Treat it as charged until safely discharged using an appropriate method and procedure. A capacitor can retain a dangerous stored charge after the supply has been switched off.

More turns generally increase inductance. The syllabus also identifies larger coil diameter and closer turn spacing as factors that increase inductance; inductors store energy in a magnetic field.

RMS is the effective value that produces the same heating effect as an equal DC value. For a sine wave, RMS is 0.707 of the peak value—not the peak value itself.

They are reciprocals: frequency f = 1/T and period T = 1/f. Frequency is in hertz (cycles per second), while period is the time for one cycle in seconds.

Reactance is opposition to AC current caused by capacitance or inductance. Impedance is the total opposition to AC current, combining resistance and reactance.

At resonance, inductive reactance and capacitive reactance are equal (XL = XC), so the net reactance cancels and the impedance is resistive. The series and parallel circuit impedances behave differently at that point.

With the same core flux, the voltage ratio follows the turns ratio: more turns on a winding gives a higher induced voltage. Current changes inversely, subject to real losses.

They reduce eddy-current losses in the core. Laminations interrupt circulating currents at low frequency; ferrite has high electrical resistance and is useful at higher frequencies.

A Zener diode can provide voltage regulation in reverse breakdown. A varactor behaves as a voltage-variable capacitor, so it can tune frequency-selective circuits electronically.

Drift can move a transmission away from its intended frequency, degrading communications and risking adjacent-channel interference. Stable oscillators and sensible operating practice help keep the transmitted signal where it belongs.

The oscillator creates a carrier, the modulator places information on it, the RF power amplifier raises the signal to the required level, and the output filter suppresses unwanted frequency products before the antenna system.

Mixing produces wanted sum or difference products as well as unwanted frequencies. Filtering selects the required product and rejects unwanted outputs that could impair reception or create interference.

Modulation depth describes the extent of amplitude variation in AM. Peak deviation describes the maximum carrier-frequency shift in FM. They apply to different modulation systems.

SSB carries information in amplitude and phase relationships. A non-linear amplifier distorts those relationships, creating splatter and unwanted signals; a linear amplifier preserves the modulation.

Data transfer rate and modulation type. Faster symbol or data rates generally require more bandwidth, while the modulation method affects how efficiently information occupies the channel.

Automatic level control (ALC) automatically limits drive or output to protect a transmitter and maintain intended operation. A manual RF power control is deliberately set by the operator to choose output level.

Sensitivity is the ability to receive weak signals. Selectivity is the ability to distinguish the wanted signal from nearby-frequency signals. A receiver can need both qualities at once.

Automatic gain control (AGC) adjusts receiver gain as signal strength changes to keep audio more usable. Receiver incremental tuning (RIT) offsets the receive frequency without moving the transmit frequency.

It is the ratio of radio-wave velocity in the line to velocity in free space. It is always less than 1, so a physical line section is shorter than its free-space electrical wavelength would suggest.

RF current on a feedline can couple into nearby devices and create interference. Where a balanced antenna is fed with unbalanced coax, use an appropriate balanced-to-unbalanced transition and routing to reduce that unwanted radiation.

They result from interaction between forward and reflected waves, usually because the transmission-line impedance and antenna load impedance are mismatched. The SWR expresses the forward/reflected relationship.

An ATU can cancel reactive components and transform the impedance presented to the transmitter. It does not change the actual SWR on the feedline segment between that transmitter-end ATU and the antenna.

ERP depends on transmitter power plus antenna-system gains and losses. It is not simply the transmitter's power setting: feedline loss and antenna gain both change the radiated result.

They are inversely related: as frequency rises, wavelength falls. In free space, use wavelength = c/f, with c approximately 300 million metres per second.

Matching polarisation improves coupling of the signal's electric field to the receive antenna. A polarisation mismatch can greatly reduce received signal strength.

The F2 layer provides the furthest HF refractions. At night, the F1 and F2 layers combine; multiple refractions, or hops, can support much longer-distance communication.

Maximum usable frequency (MUF) is the highest frequency refracted over a given path. The syllabus identifies optimum working frequency (OWF) as 15% lower than the MUF.

Strong RF can enter radio or television receiver RF/IF stages, or enter audio equipment through long speaker leads and other interconnections. The receiving device may then overload or demodulate the unwanted RF.

Its non-linearity can demodulate the RF, turning it into audible interference. This explains why an RF source may be heard through equipment that is not intended to receive amateur signals.

Low-pass passes lower frequencies; high-pass passes higher ones; band-pass selects a range; band-stop rejects a range. Choose the response that suppresses the unwanted frequency while preserving the wanted signal.

They add impedance to unwanted RF currents on leads, helping suppress conducted interference. They are a filtering aid, not a substitute for sound station layout, filtering, and appropriate operating power.

Use the minimum field strength needed for effective communication, and favour a balanced antenna system with its feedline leaving at right angles to the antenna. Both reduce unwanted coupling into nearby equipment.

Safely switch off the power. Do not touch an electric-shock casualty until the power is off; then call emergency services and provide appropriate aid such as CPR if needed and trained to do so.

A correctly rated fuse limits excessive current and helps prevent heat damage or fire. Fitting an arbitrary larger fuse can defeat that protection; follow the manufacturer or electricity authority requirement.

It lets the operator rapidly turn off all station equipment in an emergency. The switch should be easy to locate rather than hidden among equipment or cables.

Batteries contain chemicals, may emit fumes, and can explode if punctured or exposed to flames or sparks. Prevent short circuits, use suitable charging arrangements, and keep ignition sources away.

Risk varies with frequency, power, and proximity. The safe distance also depends on ERP, operating frequency, antenna type, and antenna orientation; keep people and animals clear as required.

Antennas and fittings must be suitably located and secured, and must never be connected to or sited close to mains poles or lines. Antenna erection is potentially dangerous and should be done by suitably qualified people.

Unplug radio equipment from the mains outlet and disconnect the antenna before the thunderstorm; do not operate amateur radio during it. Lightning protection is good practice, but it does not make operation during a thunderstorm safe.

Frequent SWR checks help avoid transmitter damage and potential interference. A multimeter is used to measure voltage, current, and resistance; use the correct function, range, and connection method for the quantity being measured.