FCC Commercial Radio cheat sheet

FCC Part 80 governs the Maritime Radio Service; Part 13 covers commercial radio operator licenses. The commercial operator license classes are Restricted Radiotelephone Operator Permit, Marine Radio Operator Permit (MP), General Radiotelephone Operator License (GROL), and Global Maritime Distress and Safety System (GMDSS) Operator License.

The MP is required to operate radiotelephone equipment on vessels required to carry a radio under Part 80; it is also required for certain coast station and aviation operators. The GROL is required for commercial ship radar and for repair/maintenance of licensed radio transmitting equipment.

Distress signal priorities: MAYDAY (distress), PAN-PAN (urgency), SECURITE (safety). Distress traffic has absolute priority over all other communications; urgency and safety follow in that order.

The standard distress frequencies are 156.8 MHz (VHF channel 16) and 2182 kHz (MF radiotelephone). Digital selective calling (DSC) distress alerting uses VHF channel 70 (156.525 MHz) and MF/HF DSC frequencies; voice may not be transmitted on channel 70.

Station identification: transmit the station's call sign at the beginning and end of each communication and at least every 15 minutes during a long communication. Use the vessel name or call sign; do not use unofficial identifiers.

A radiotelephone station log must be kept when required by the station license or by Part 80 rules; entries include distress, urgency, and safety communications, and must be retained for at least one year (or as specified by rule).

Third-party traffic: messages originating from or destined to persons other than the station licensee may be handled only where permitted by the license and applicable rules; distress, urgency, and safety traffic is always permitted.

Prohibited transmissions include false distress signals, obscene or profane language, superfluous communications, and transmissions that interfere with distress, urgency, or safety communications. Violations can result in fines, license suspension, or revocation.

Silence periods: on 2182 kHz, the three-minute periods beginning at 00 and 30 minutes past each hour are reserved for distress, urgency, and safety traffic. On VHF channel 16, keep transmissions brief and move to a working channel.

Frequency and wavelength: λ (meters) = 300 / f (MHz). Example: 156.8 MHz → λ ≈ 1.91 m. Lower frequencies have longer wavelengths and generally better ground-wave propagation; higher frequencies support line-of-sight and skywave.

Power relationships: dB = 10 log10(P2/P1). Doubling power is +3 dB; halving is −3 dB; a factor of 10 is +10 dB. Voltage ratios use 20 log10(V2/V1).

Ohm's law and power: V = IR; P = VI = I²R = V²/R. For a 50-ohm system, 100 W corresponds to V = √(PR) ≈ 70.7 V RMS and I ≈ 1.41 A.

Modulation: AM varies carrier amplitude; FM varies carrier frequency. FM has better immunity to amplitude noise but requires greater bandwidth (Carson's rule: BW ≈ 2(Δf + fm)). Deviation and modulation index determine occupied bandwidth.

Antenna fundamentals: a half-wave dipole has feedpoint impedance near 73 ohms and gain of about 2.15 dBi. A quarter-wave vertical over a ground plane has about 36 ohms impedance and a low radiation angle suitable for marine VHF.

Standing wave ratio (SWR): SWR = (1 + |Γ|)/(1 − |Γ|), where Γ is the reflection coefficient. SWR of 1:1 is ideal; values above about 2:1 indicate mismatch and require investigation of feedline and antenna.

Propagation: VHF/UHF are essentially line-of-sight, with range extended by antenna height (radio horizon ≈ 1.23√h in nautical miles for h in feet). MF uses ground wave; HF supports skywave via ionospheric refraction, varying with time of day and solar activity.

Batteries and power: a lead-acid battery's capacity is rated in ampere-hours; reserve capacity and depth of discharge affect available operating time. Emergency batteries must be kept charged and tested per the station's requirements.

Interference and filtering: co-channel interference comes from another station on the same frequency; adjacent-channel interference is reduced by selectivity. Receiver sensitivity determines the weakest usable signal; selectivity determines rejection of nearby signals.