ACMA Standard Theory Cheat Sheet

Cheat sheet ACMA Standard Theory Cheat Sheet Practice Questions Study Guide Print / Save PDF

Mathematics Not published of exam Arithmetic Fractions and percentages SI prefixes Formula calculations

Technical Basics Not published of exam Circuit quantities Passive components AC theory Semiconductors Power supplies

Transmitters and Receivers Not published of exam Transmitter stages Modulation Receiver stages Mixer products Amplifier classes

Transmission Lines and Antennas Not published of exam Feedline losses Standing wave ratio Matching units Antenna patterns Effective radiated power

Propagation Not published of exam Wavelength Polarisation Ionospheric layers MUF and OWF Fading

Interference and EMC Not published of exam Interference paths Receiver overload Filters Ferrite chokes Station layout

Safety Not published of exam Mains hazards Battery hazards Antenna erection Lightning RF exposure

Measurements Not published of exam Frequency checks RF power SWR meter Multimeter Calibration limits

Quick Facts Paper Standard theory Format 50 multiple-choice questions Time 60 minutes Pass mark 70% · 35 correct Authority ACMA Delivery Accredited assessor Exam fee Free Formula sheet Provided Coverage Parts 3–8, 10–11 Assumed knowledge Foundation syllabus

Formula Triangles MA Cover the wanted quantity E over I×R P over E×I Then rearrange

Formula Core MA Ohm voltage E=IR Ohm current I=E/R Ohm resistance R=E/I DC power P=EI Power via current P=I²R Power via voltage P=E²/R Period T=1/f seconds Frequency f=1/T hertz Wavelength λ(m)=300/f(MHz) Efficiency RF output/input × 100%

Reactance vs Impedance TE

Reactance Inductive or capacitive Frequency dependent Part of impedance

Impedance Total AC opposition Includes resistance Whole circuit quantity Component effect versus total opposition

Component Combinations TE Series resistors Values add Parallel resistors Reciprocals add Series capacitors Reciprocals add Parallel capacitors Values add Series inductors Values add Parallel inductors Reciprocals add Capacitance Electric-field storage Inductance Magnetic-field storage Polarised capacitor Observe polarity Capacitor charge Can remain dangerous

Series vs Parallel Tuning TE

Series tuned Low resonant impedance Current becomes large XL equals XC

Parallel tuned High resonant impedance Supply current becomes small XL equals XC Series low; parallel high

AC, Tuning, and Transformers TE RMS sine 0.707 × peak One cycle 360 degrees Reactance Component AC opposition Impedance Total AC opposition Resonance XL=XC Resonant impedance Purely resistive Q factor Lower losses mean higher Q Series tuning Low resonant impedance Parallel tuning High resonant impedance Transformer voltage Follows turns ratio Transformer current Inverse turns ratio Laminations Reduce eddy currents

Power and Semiconductors TE Half-wave rectifier One half-cycle Full-wave rectifier Both half-cycles Bridge rectifier Four-diode full-wave Smoothing Reduces ripple Diode PIV Must exceed reverse peak Forward voltage Diode conduction drop Zener diode Voltage regulation Varactor diode Voltage-variable capacitance NPN or PNP Common-emitter stage FET Common-source stage Transistor internals Not required

Sensitivity vs Selectivity RA

Sensitivity Weak-signal ability Signal strength limit Not adjacent rejection

Selectivity Separates nearby signals Filter bandwidth matters Not weak-signal ability Hear weak versus reject nearby

Transmitter Chain RA Audio input Processes microphone signal Carrier oscillator Creates RF carrier VFO Tunes operating frequency Mixer Converts frequency Multiplier Raises carrier frequency Modulator Adds information Driver Feeds output stage Power amplifier Raises RF power Output filter Suppresses unwanted emissions ALC Limits transmitter drive Linear amplifier Preserves waveform Duty cycle Affects power rating

ALC vs AGC RA

ALC Transmitter control Limits amplifier drive Prevents excess output

AGC Receiver control Adjusts receiver gain Stabilises audio level ALC transmits; AGC receives

Modulation and Data RA AM Carrier amplitude varies FM Carrier frequency varies SSB One sideband, carrier suppressed AM depth Modulation amount FM deviation Peak frequency shift Morse On-off carrier keying RTTY Frequency-shift keying PSK Carrier phase shifts Packet Data frames over radio Digital bandwidth Rises with data rate

Receiver Chain RA Sensitivity Weakest usable signal Selectivity Rejects nearby signals SNR Signal versus noise RF amplifier Boosts received RF Mixer and LO Create intermediate frequency IF amplifier Fixed-frequency gain and filtering Crystal filter Sharp IF selectivity Ceramic filter IF selectivity Demodulator Recovers information Audio amplifier Drives speaker AGC Stabilises received level RIT Offsets receive frequency Shared stages Oscillators and IF

ATU vs Balun AN

ATU Transforms impedance Tunes reactive load May sit transmitter-side

Balun Balanced-unbalanced interface Limits feedline radiation Useful with coaxial feed Match impedance versus balance currents

Feedlines and Matching AN Velocity factor Always below one Line loss Rises with frequency VHF feedline Low loss matters Balanced antenna Use balun with coax Balun Limits feedline radiation Mismatch Creates reflected waves Standing waves Forward plus reflected SWR Mismatch indicator Acceptable SWR 1.5:1 or lower High SWR Raises feedline loss ATU Transforms impedance Shack ATU Line SWR remains

Antennas and ERP AN Antenna length Falls as frequency rises Dipole Half-wave, centre-fed Folded dipole Higher feedpoint impedance Ground plane Quarter-wave vertical Yagi Directional array End-fed wire Fed near one end Low radiation angle Favours long-distance paths Polarisation Set by electric field ERP Add gains; subtract losses Feedline exit Leave antenna at right angles

Layer Ladder PR D absorbs; F goes far D: daytime absorption F2: longest single hop Night: F layers combine

MUF vs OWF PR

MUF Highest refracted frequency Path specific Upper usable boundary

OWF Preferred working frequency 15% below MUF Adds operating margin Maximum limit versus working choice

Ionospheric Propagation PR Radio speed 300 million metres/second Electric field Perpendicular magnetic field Free space Straight-line spreading D layer Daytime low-frequency absorption E layer Ionospheric refraction Daytime F1/F2 Separate upper layers Night F layer F1 and F2 combine F2 hop About 4000 km Multiple hops Worldwide paths Fading Received strength varies MUF Highest refracted frequency OWF 15% below MUF Seasonal change Alters useful bands

EMC First Aid EM Power down, route right, filter entry Minimum useful power Feedline exits right-angle Filter entry path

Interference Triage EM Neighbour reports interference → Stay diplomatic ( Gather symptoms ) Every transmission triggers it → Check station first ( Connections and earth ) Only high power triggers it → Reduce RF power ( Retest ) Audio reproduces your voice → Add ferrite filtering ( Audio-lead entry ) Receiver front end overloads → Suitable RF filter ( At victim input ) Coax feeds balanced antenna → Install balun ( Reduce common-mode current ) Feedline parallels antenna → Reroute at right angles ( Reduce coupling ) Problem persists → Seek technical advice ( ACMA may assist )

EMC Control EM RF-stage entry Antenna-path interference IF-stage entry Receiver conversion path Audio entry Long leads conduct RF Wideband amplifiers Strong-signal overload Audio nonlinearity Demodulates RF Low-pass filter Passes lower frequencies High-pass filter Passes higher frequencies Band-pass filter Passes selected band Notch filter Rejects selected band Ferrite beads Suppress common-mode RF Balanced antenna Usually fewer EMC issues Minimum power Reduces field strength Feedline routing Right angle from antenna Vehicle EMC Protect electronic controls Neighbour complaint Use diplomacy

Shock Response SA Switch off before touching Isolate power first Call emergency services CPR may follow

Station Safety SA High voltage/current Both are dangerous Approval label Required mains equipment Safety earth Provides fault path Active-lead fuse Limits excess current Fuse replacement Use specified rating Damaged lead Authorised repair only Emergency switch Clearly marked OFF Electrical accident First isolate power Shock casualty Never touch while powered Emergency response Call help; consider CPR Batteries Fumes, chemicals, explosion Antenna exclusion Protect people and animals RF danger Frequency, power, proximity Safe distance Depends on ERP and antenna Antenna erection Use qualified persons Mains lines Keep antennas well clear Thunderstorm Disconnect; never operate Headphones Avoid excessive volume Station security Block unauthorised access

Measurement Picker ME Check transmitter frequency → Frequency counter ( Mind calibration ) Need external reference → Standard transmission ( Availability varies ) Check dial calibration → Crystal calibrator ( Spot frequencies ) Measure RF output → Calibrated power device Check antenna match → SWR meter Measure potential difference → Voltmeter mode ( Across circuit ) Measure circuit current → Ammeter mode ( Through circuit ) Measure resistance → Ohmmeter mode ( Power off first )

Test Instruments ME Crystal calibrator Frequency reference Frequency counter Direct frequency reading Standard transmission External frequency reference RF power Use calibrated device SWR meter Checks matching Multimeter voltage Connect across circuit Multimeter current Connect through circuit Multimeter resistance Power circuit off

Common Traps

Theory is not certification Theory is one component ≠ Regulations and practical remain

Shack ATU limits Transforms presented impedance ≠ Antenna-side line SWR remains

SWR meaning SWR indicates mismatch ≠ Feedline loss also matters

Gain-control mix-up ALC controls transmission ≠ AGC controls reception

OWF direction OWF sits below MUF ≠ Subtract fifteen percent

Electrical casualty Isolate power first ≠ Never touch while energised

Amplifier power rating Duty cycle changes loading ≠ Mode choice affects heating

Filter direction Low-pass keeps lower frequencies ≠ High-pass keeps higher frequencies

Last Minute 1 . Memorise every supplied formula 2 . Practise same-value component networks 3 . Trace transmitter blocks in order 4 . Trace superhet receiver blocks 5 . Match filters to entry paths 6 . Know SWR and ATU limits 7 . Recall five named antennas 8 . Sketch ionospheric layers 9 . Separate MUF from OWF 10 . Choose each measuring instrument 11 . Rehearse electrical accident response 12 . Check formula-sheet units 13 . Target at least 35 correct 14 . Answer all 50 questions

ACMA Amateur Radio Standard Recognition Certificate - Theory Practice Questions 120 questions Study Guide 57 topics Cheat Sheet 155 facts Flashcards 50 cards Shorts 1 short Podcast

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