Foundation Amateur Radio Exam cheat sheet

US amateur licenses: Technician, General, Extra; each higher class grants all privileges of the classes below it, and exams are administered by Volunteer Examiners (VEs).

ITU regions: Region 1 = Europe/Africa/Middle East, Region 2 = Americas, Region 3 = Asia-Pacific; frequency allocations differ between regions.

Callsign structure (US): one or two prefix letters, a digit (call area 0-9), then 1-3 suffix letters; e.g., a callsign beginning with A, K, N, or W is a US call.

Station identification: give your callsign at the start and end of each contact and at least every 10 minutes during a contact; use phone, CW, or digital mode as appropriate.

Control operator: the person responsible for the station's transmissions; the station licensee must designate a control operator, and both share responsibility for compliance.

Third-party traffic: messages sent on behalf of a non-licensed person; international third-party traffic is restricted, while domestic third-party traffic is generally permitted.

Prohibited transmissions: obscenity, profanity, music, broadcasting, business communications (except as specifically allowed), and communications for pecuniary interest.

Emergency communications: any station may use any frequency or mode to assist in an emergency involving immediate danger to life or property, and must identify appropriately.

Power limits: Technician and General class HF privileges are limited to 1500 W PEP output; specific bands and modes vary by license class.

Ohm's law: V = I × R; power: P = V × I = I²R = V²/R; these three relationships solve most circuit problems.

Series circuits: resistances add (R_total = R1 + R2 + ...); parallel circuits: 1/R_total = 1/R1 + 1/R2 + ..., and total resistance is less than the smallest branch.

Frequency and wavelength: wavelength (m) = 300 / frequency (MHz); a 146 MHz signal has a wavelength of about 2 meters.

Decibels: dB = 10 log10(P2/P1) for power; doubling power is about +3 dB, tenfold power is +10 dB, and halving power is about -3 dB.

Capacitors store energy in an electric field (oppose DC, pass AC); inductors store energy in a magnetic field (pass DC, oppose AC changes); reactance depends on frequency.

Resonance: at resonance, inductive reactance equals capacitive reactance (X_L = X_C), and the circuit presents a purely resistive impedance.

AC and RMS: for a sine wave, RMS voltage = peak voltage / √2 ≈ 0.707 × peak; RMS values are used for power calculations.

Transformers: voltage ratio equals turns ratio; a step-down transformer reduces voltage and increases current, with power approximately conserved.

Electrical safety: fuses and circuit breakers protect wiring from overload; the green or green/yellow wire is the safety ground in AC mains wiring.

Modulation types: AM varies carrier amplitude, FM varies carrier frequency, SSB transmits one sideband with no carrier, and CW is on-off keyed carrier.

SSB advantages: narrower bandwidth (about 3 kHz) and higher power efficiency than AM, since no carrier or duplicate sideband is transmitted.

FM deviation and bandwidth: wider deviation improves signal-to-noise ratio but increases occupied bandwidth (Carson's rule: BW ≈ 2 × (deviation + highest modulating frequency)).

Receiver sensitivity: the minimum signal a receiver can detect; selectivity is the ability to reject adjacent signals; both are key receiver specifications.

Superheterodyne receiver: mixes incoming RF with a local oscillator to produce a fixed intermediate frequency (IF), where filtering and amplification occur.

Mixer function: combines two signals to produce sum and difference frequencies; the difference frequency is the IF in a superheterodyne receiver.

Transmitter stages: oscillator generates the carrier, buffer isolates the oscillator, amplifier boosts power, and the final stage delivers power to the antenna.

Spurious emissions: unwanted signals outside the intended bandwidth; filters and proper tuning reduce harmonics, which are multiples of the fundamental frequency.

Duty cycle and power: average power = peak power × duty cycle; SSB and CW have lower duty cycles than FM, so they produce less heating for the same PEP.

Dipole length: a half-wave dipole is about 468 / frequency (MHz) feet long, or 143 / frequency (MHz) meters.

Feed line impedance: common coaxial cable is 50 ohms; a half-wave dipole in free space is about 73 ohms, so a 1:1 SWR is not achievable with 50-ohm coax alone.

SWR: standing wave ratio measures impedance match; 1:1 is perfect, 2:1 is generally acceptable, and high SWR reduces radiated power and can damage transmitters.

Antenna gain: measured in dBi (relative to isotropic) or dBd (relative to dipole); dBd = dBi - 2.15; gain comes at the expense of directionality.

Polarization: horizontal and vertical polarization should match between stations; cross-polarization can cause significant signal loss, especially on VHF/UHF.

Ionospheric layers: D, E, F1, and F2; the F layer supports long-distance HF propagation, while the D layer absorbs lower-frequency signals during daylight.

Propagation modes: ground wave (low HF and below), sky wave (HF via ionosphere), and line-of-sight (VHF/UHF, extended by repeaters and tropospheric ducting).

Solar cycle: higher sunspot numbers increase ionization, raising the maximum usable frequency (MUF) and improving long-distance HF propagation.

Velocity factor: signals travel slower in cable than in free space; velocity factor (e.g., 0.66 for some coax) affects electrical length and phasing.