GROL cheat sheet

The General Radiotelephone Operator License (GROL) is issued under FCC Part 13 after passing Element 1 (basic radio law and operating practice, 24 questions, 18 correct to pass) and Element 3 (electronic fundamentals and techniques, 50 questions, 38 correct to pass).

Commercial radio operator licenses are issued for the lifetime of the holder; they do not expire or require renewal, but the FCC may revoke, suspend, or modify them.

FCC Part 80 covers ship stations, Part 87 aircraft stations, Part 97 the amateur service, and Part 2 the frequency allocations and international treaties that implement the ITU Radio Regulations domestically.

A ship station requires a station license, and the operator must hold the proper operator license; the license (or a copy) must be available at the station for inspection.

Only a qualified licensed operator may make transmitter adjustments that could cause off-frequency operation, excessive power, or spurious radiation; no one may exceed authorized power or operate outside assigned frequencies.

Ship stations identify by vessel name and assigned call sign; transmissions must be limited to the minimum necessary, and superfluous signals, obscene language, and false distress calls are prohibited.

Operators must not intercept and divulge the contents of messages not addressed to them, except distress, urgency, or safety traffic or communications lawfully received for rebroadcast.

The licensee is responsible for every transmission made from the station, regardless of who actually operates the equipment.

The radiotelephone distress signal MAYDAY, spoken three times, is sent on 2182 kHz or VHF channel 16 (156.800 MHz) and is followed by vessel name, position, nature of distress, assistance required, and number of persons aboard.

PAN PAN, spoken three times, is the urgency signal for messages concerning the safety of a vessel or person when there is no immediate danger; SECURITE, spoken three times, precedes safety messages such as navigation warnings.

On hearing a distress call, all stations must stop transmissions capable of causing interference and maintain radio silence on the distress frequency until it is clear no assistance is needed.

A DSC distress alert is sent on VHF channel 70 or 2187.5 kHz (MF), then followed by a voice MAYDAY on channel 16 or 2182 kHz; channel 70 must never carry voice traffic.

Silence periods of three minutes begin at H+00 and H+30 each hour on 2182 kHz and are reserved for distress calls and the replies to them.

VHF channel 16 is the distress, safety, and calling channel; channel 13 (156.650 MHz) is bridge-to-bridge; channel 6 is inter-ship safety; channel 9 is the US boating calling channel.

A bridge-to-bridge radiotelephone is required on power-driven vessels 20 meters or more in length and must be monitored for navigation safety traffic.

GMDSS defines Sea Area A1 (VHF DSC coverage near coast stations), A2 (MF), A3 (Inmarsat or HF), and A4 (polar regions beyond satellite coverage).

A false distress alert must be cancelled promptly by a broadcast to all stations on the distress frequency stating the station identity and the time and date of the false alert.

Ohm's law: V = IR. Power: P = VI = I²R = V²/R.

Series resistances add (R = R1 + R2 + ...); parallel conductances add, and for two resistors in parallel R = (R1·R2)/(R1 + R2).

Capacitive reactance Xc = 1/(2πfC); inductive reactance Xl = 2πfL; reactance rises with frequency for inductors and falls for capacitors.

Series resonance occurs when Xl = Xc, at f = 1/(2π√(LC)); impedance then is minimum and purely resistive.

Impedance of a series RLC circuit: Z = √(R² + (Xl − Xc)²), with phase angle θ = arctan((Xl − Xc)/R).

RMS = 0.707 × peak, peak = 1.414 × RMS, and peak-to-peak = 2 × peak; the average of a full-wave rectified sine is 0.637 × peak.

Decibels: dB = 10 log(P2/P1) = 20 log(V2/V1); +3 dB doubles power, +10 dB multiplies power by 10, −3 dB halves it.

Silicon diodes drop about 0.7 V forward and germanium about 0.3 V; transistor beta = Ic/Ib, and a bipolar transistor is in cutoff when the base-emitter junction is not forward biased.

RC time constant τ = RC; after one time constant a capacitor charges to 63.2% of the applied voltage.

Transformer relations: Vs/Vp = Ns/Np, and the impedance ratio equals the square of the turns ratio; coil Q = X/R, and skin effect reduces the effective cross-section of a conductor as frequency rises.

A linear power supply runs transformer → rectifier → filter → regulator; half-wave rectification gives ripple at the line frequency and full-wave or bridge at twice the line frequency (120 Hz from 60 Hz mains).

Ripple is reduced by larger filter capacitance, lighter load current, and additional LC or active filtering; a dried-out filter capacitor shows up as 120 Hz hum.

Class A conducts through 360° of the cycle with low efficiency; Class B conducts 180° and is used push-pull; Class AB lies between; Class C conducts less than 180° and is highly efficient but requires a tuned output circuit.

An oscillator needs positive feedback with loop gain of at least one and a total loop phase shift of 0° or 360°; Colpitts uses a capacitive divider, Hartley a tapped inductor, and Pierce a crystal.

Crystal oscillators have very high Q and therefore excellent frequency stability compared with LC oscillators.

The half-split troubleshooting method divides the signal path in two, tests at the midpoint, and successively narrows the faulty stage; signal tracing follows the signal from input to output.

A transmitter must never be tested without a suitable dummy load; high VSWR or an open antenna can destroy the final amplifier.

Mixers and frequency multipliers generate sum and difference products and harmonics; undesired products are removed with tuned circuits or filters.

Automatic level control (ALC) limits drive to prevent overmodulation, and heat sinks or forced air keep transistor junction temperatures within ratings.

An emission designator gives the necessary bandwidth as three digits plus a letter (H = hectohertz, M = megahertz, k = kilohertz), followed by three symbols for main-carrier modulation, nature of the modulating signal, and nature of the information.

A3E is AM double-sideband telephony; J3E is SSB suppressed-carrier telephony; F3E is FM telephony; A1A is on-off keyed CW telegraphy; F1B is FM automatic telegraphy.

First symbol (main carrier): A = AM double sideband, H = SSB full carrier, R = SSB reduced carrier, J = SSB suppressed carrier, B = independent sidebands, C = vestigial sideband, F = frequency modulation, G = phase modulation, P = pulse.

Second symbol: 0 = no modulating signal, 1 = digital single channel without subcarrier, 2 = digital with subcarrier, 3 = analog single channel, 7, 8, 9 = multiple channels.

Third symbol: E = telephony, D = data, B = telegraphy for automatic reception, N = no information, W = combination of telegraphy, data, and telephony.

AM modulation index m = (Emax − Emin)/(Emax + Emin); total power Pt = Pc(1 + m²/2); AM bandwidth equals twice the highest modulating frequency (about 6 kHz for voice).

FM bandwidth follows Carson's rule: BW ≈ 2(Δf + fm); deviation ratio is peak deviation divided by the highest modulating frequency.

An SSB signal occupies roughly 3 kHz and concentrates all transmitted power in one sideband, whereas AM DSB with carrier needs about twice the bandwidth.

A mixer output contains the sum and difference of the input frequencies, and the superheterodyne intermediate frequency is chosen so the image response falls outside the preselector passband.

A square wave contains only odd harmonics; Fourier analysis resolves any periodic non-sinusoidal waveform into a fundamental plus harmonics.

Length in feet: half-wave dipole = 468/f(MHz), quarter-wave vertical = 234/f(MHz); in meters use 143/f(MHz) and 71.5/f(MHz).

A center-fed half-wave dipole in free space presents about 73 ohms at resonance; a quarter-wave vertical over a good ground plane presents about 36 ohms and radiates at a low angle.

Antenna gain in dBd (referenced to a half-wave dipole) equals gain in dBi minus 2.15 dB.

Reflection coefficient Γ = (Zload − Z0)/(Zload + Z0); VSWR = (1 + |Γ|)/(1 − |Γ|). A 2:1 VSWR reflects about 11% of the incident power.

Characteristic impedance of a lossless line is Z0 = √(L/C); coaxial cable loss increases with frequency and with higher VSWR.

Physical length = electrical length × velocity factor; solid polyethylene coax has a velocity factor of about 0.66, so a quarter wave is shortened accordingly.

A balun couples a balanced line or antenna to unbalanced coaxial feed line and suppresses current on the outside of the coax shield.

ERP = transmitter power × antenna gain relative to the reference; EIRP references an isotropic radiator.

Gain rises and beamwidth narrows as antenna size increases in wavelengths; a parabolic dish has gain G = η(πD/λ)².

Ionospheric layers are D, E, F1, and F2; the D layer absorbs HF energy during daylight, and the F2 layer has the highest electron density and supports the longest skywave paths.

Ground waves follow the earth's surface and dominate at MF and below, traveling best over seawater; space waves serve VHF and UHF line-of-sight paths.

Critical frequency is the highest frequency reflected straight up; the maximum usable frequency is approximately fc / cos θ, where θ is the incidence angle from vertical.

The skip zone lies between the end of reliable ground-wave range and the nearest skywave return; skip distance increases as frequency rises.

Radio horizon in nautical miles ≈ 1.23√(antenna height in feet); in kilometers ≈ 4.12√(antenna height in meters).

Solar activity follows an approximately 11-year cycle; higher sunspot numbers raise the MUF and improve long-distance HF propagation.

Temperature inversions and sharp humidity gradients produce tropospheric ducting and superrefraction, extending VHF and UHF range well beyond the horizon.

Sporadic E supports occasional long VHF hops, mainly in summer; atmospheric absorption and rain attenuation increase sharply above 10 GHz.

Free-space path loss increases by 6 dB whenever the distance or the frequency is doubled.

A superheterodyne receiver runs RF amplifier → mixer with local oscillator → IF amplifier and filter → detector → audio; the IF stage provides most of the gain and determines selectivity.

Image frequency = RF ± 2 × IF; a higher IF, a preselector, or a tuned RF stage reduces the image response.

Sensitivity is set by noise figure and bandwidth; selectivity by the IF filter shape factor; dynamic range by front-end linearity.

AGC reduces gain on strong signals to hold audio output constant; ALC limits transmitter drive; squelch mutes receiver output when no carrier is present.

Harmonics are integer multiples of the carrier and are attenuated with low-pass or band-pass filters at the transmitter output.

Intermodulation, cross-modulation, and desensitization occur when strong off-frequency signals drive a receiver front end into nonlinear operation.

Transmitter chain: oscillator → buffer → frequency multiplier → driver → power amplifier → harmonic filter → antenna.

Splatter (adjacent-channel interference) results from overmodulation or nonlinear amplification; key clicks come from poorly shaped keying waveforms.

Peak envelope power is the average power at the crest of the modulation envelope; duty cycle determines average power and device heating.

Marine radar uses X band 9.3–9.5 GHz (about 3 cm) for narrow beamwidth and high resolution, and S band 2.9–3.1 GHz (about 10 cm) for rain penetration and longer range.

Radar range = c × t / 2; radio energy travels about 150 meters per microsecond, so a 12.36 microsecond round trip corresponds to 1 nautical mile.

Pulse repetition frequency sets the maximum unambiguous range (Rmax = c/2·PRF); pulse width sets minimum range and range resolution (cτ/2).

A magnetron generates the radar pulse; in rectangular waveguide the dominant TE10 mode has cutoff frequency fc = c/(2a) for broad-wall dimension a.

A SART responds on 9 GHz with a line of twelve dots on a rescuing vessel's radar; a RACON is a fixed beacon that marks a navigation hazard.

AIS operates on VHF channels 87B and 88B (161.975 and 162.025 MHz) and supplements but never replaces radar and visual watchkeeping.

An EPIRB transmits a 406 MHz alert to COSPAS-SARSAT and provides a 121.5 MHz homing signal for search aircraft.

NAVTEX broadcasts navigational and meteorological warnings on 518 kHz in English for international service; GMDSS Sea Area A1 lies within VHF DSC coverage of coast stations, roughly 20 to 30 nautical miles.