FCC Commercial Radio flashcards

33 cards. Read the term and the definition here. The deck at the top of this page is optional.

MAYDAY

International radiotelephone distress signal indicating a vessel or person is in grave and imminent danger and requires immediate assistance. It has absolute priority over all other transmissions.

PAN-PAN

International radiotelephone urgency signal used when a station has an urgent message concerning the safety of a vessel or person but is not in immediate grave danger. It ranks below MAYDAY but above routine traffic.

SECURITE

International radiotelephone safety signal announcing a message about navigation or weather safety, such as a storm warning or navigational hazard. It ranks below MAYDAY and PAN-PAN.

VHF channel 16

156.8 MHz, the international radiotelephone distress, urgency, and safety frequency. Initial calls are made here, then stations move to a working channel for routine conversation.

VHF channel 70

156.525 MHz, reserved exclusively for digital selective calling (DSC). Voice transmissions are prohibited on this channel because they would interfere with DSC alerting.

MF distress frequency

2182 kHz is the international MF radiotelephone distress and calling frequency. Silence periods occur during the first three minutes of each half hour.

Marine Radio Operator Permit

The MP license authorizes operation of radiotelephone equipment on vessels required to carry radios under Part 80. It does not cover radar or equipment repair.

GROL

General Radiotelephone Operator License. Required for operating and maintaining commercial ship radar and for repair of licensed radio transmitting equipment.

Station identification

Transmit the station call sign at the start and end of each communication and at least every 15 minutes during a long communication. Vessel name may accompany the call sign.

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. Other stations must not transmit then.

False distress signal

A knowingly transmitted false distress call or message is prohibited by rule and can lead to fines, license suspension, or criminal penalties. It also endangers real rescue operations.

Third-party traffic

Messages originating from or destined to persons other than the station licensee. They may be handled only where the license and applicable rules permit; distress traffic is always allowed.

Station log retention

When a radiotelephone station log is required, entries include distress, urgency, and safety communications. The log must be retained for the period specified by rule, generally one year.

Part 80

The FCC rules governing the Maritime Radio Service, including licensing, frequencies, operating procedures, and required equipment for ship and coast stations.

Prohibited transmissions

False distress signals, obscene or profane language, superfluous communications, and any transmission interfering with distress, urgency, or safety traffic are prohibited and subject to enforcement action.

DSC distress alert

A digital selective calling distress alert sent on VHF channel 70 or MF/HF DSC frequencies. It automatically includes the vessel identity and nature of distress, and is normally followed by voice on channel 16.

Wavelength formula

Wavelength in meters equals 300 divided by frequency in megahertz. For example, 156.8 MHz gives a wavelength of about 1.91 meters.

Decibel power ratio

dB equals 10 times the base-10 logarithm of the power ratio. Doubling power is +3 dB, halving is −3 dB, and a tenfold increase is +10 dB.

Ohm's law

Voltage equals current times resistance (V = IR). Combined with P = VI, this gives P = I²R and P = V²/R for resistive circuits.

Half-wave dipole

A dipole antenna one half wavelength long. Its feedpoint impedance is near 73 ohms and its gain is about 2.15 dBi relative to an isotropic radiator.

Quarter-wave vertical

A vertical radiator one quarter wavelength long used with a ground plane. Feedpoint impedance is about 36 ohms and the low radiation angle suits marine VHF communications.

Standing wave ratio

SWR equals (1 + |Γ|) divided by (1 − |Γ|), where Γ is the reflection coefficient. A 1:1 SWR is ideal; values above about 2:1 indicate a mismatch.

Carson's rule

Approximate FM bandwidth equals twice the sum of peak deviation and the highest modulating frequency. It estimates the occupied bandwidth of an FM signal.

Radio horizon

The line-of-sight distance to the horizon, extended by antenna height. A common approximation is 1.23 times the square root of antenna height in feet, in nautical miles.

Ground wave

Propagation along the earth's surface, dominant at MF and lower HF. It provides reliable short-range coverage and is less affected by time of day than skywave.

Skywave propagation

HF signals refracted by the ionosphere back to earth, enabling long-distance communication. Reliability varies with frequency, time of day, season, and solar activity.

Receiver sensitivity

The weakest signal a receiver can detect and reproduce with acceptable output quality. It is often specified in microvolts or dBm at a given signal-to-noise ratio.

Receiver selectivity

The ability of a receiver to reject signals on frequencies adjacent to the desired signal. It is determined mainly by intermediate-frequency filter characteristics.

Co-channel interference

Interference caused by another station transmitting on the same frequency. It cannot be removed by receiver selectivity and is resolved by frequency coordination or reduced power.

Amplitude modulation

A modulation method in which the carrier amplitude varies with the modulating signal. It occupies bandwidth of about twice the highest modulating frequency and is susceptible to amplitude noise.

Frequency modulation

A modulation method in which the carrier frequency varies with the modulating signal. It resists amplitude noise but needs greater bandwidth, estimated by Carson's rule.

Antenna feedline loss

Signal power lost in the transmission line between transmitter and antenna, usually expressed in dB per unit length. Higher loss reduces effective radiated power and can mask a poor SWR.

Ampere-hour rating

A battery capacity rating equal to the current in amperes multiplied by the discharge time in hours. Available capacity decreases at high discharge rates and with age.