A group of bits including data and control elements which is transmitted as a whole.
Packet Controller.
Term used for a hardware TNC (Terminal Node Controller) with an on-board modem.
Packet Radio.
A
system of digital communication whereby information is broken into short bursts. The bursts ("packets") also contain callsign, addressing and error-detection information. See also: Digital Modes page.
PACTOR.
A radio modulation mode for sending digital data via radio waves. It is most commonly used on HF.
PACTOR is an evolution of both AMTOR and packet radio, hence the name PACTOR. It was developed in order to improve the reception of digital data when the received signal was weak or noisy. PACTOR combines the bandwidth efficiency of packet radio and the error-correction and automatic repeat request of AMTOR. See also: Digital Modes page.
Parabolic Antenna.
A high-gain reflector antenna used for radio, television and data communications, and also for radiolocation (RADAR), on the UHF and SHF parts of the electromagnetic spectrum. The relatively short wavelength of electromagnetic (radio) energy at these frequencies allows reasonably sized reflectors to exhibit the very desirable highly directional response for both receiving and transmitting. Also called a Dish Antenna.
Parallel Circuit.
An electrical circuit in which the electrons follow more than one path in going from the negative supply terminal to the positive terminal.
Parallel Conductor Feed Line.
Feed Line constructed of two wires held at a constant distance apart; either incased in plastic or constructed with insulating spacers placed at intervals along the line.
Parasitic Beam Antenna.
A name for a type of beam antenna.
Parasitic Element.
Part of a directive antenna that derives energy from mutual coupling with the driven element. Parasitic elements are not connected directly to the feed line.
Pass Band Tuning (PBT).
A function that electronically reduces interference by narrowing IF bandwidth.
The time interval between one event and another in a regularly recurring cycle.
Phased Antenna Array (Phased Array).
A group of 2 or more antennas in which the relative phases of the respective signals feeding the antennas are varied in such a way that the effective radiation pattern of the array is reinforced in a desired direction and suppressed in undesired directions.
A self-correcting feedback circuit used in VFO's or frequency synthesizers to provide a stable radio frequency source for receivers and transmitters.
Phase Modulation (PM) .
A form of modulation that represents information as variations in the instantaneous phase of a carrier wave. Unlike its more popular counterpart, frequency modulation (FM), PM is not very widely used, this is because it tends to require more complex receiving hardware and there can be ambiguity problems with determining whether, for example, the signal has 0° phase or 180° phase.
Phase Shift Keying (PSK).
A method of transmitting digital information in which the phase of the carrier is varied in accordance with the digital signal. See also: AFSK, FSK, MSK, Digital Modes page.
Phone.
Another name for voice communications.
Phone Emission.
Another name for voice communications.
Phonetic Alphabet.
(Properly: NATO Phonetic Alphabet or International Radiotelephony Spelling Alphabet). Standard words used on voice modes to make it easier to understand letters of the alphabet, such as those in call signs. The call sign GW4LFO stated phonetically is Golf Whiskey Four Lima Foxtrot Oscar. Each page of this glossary is headed by the letter for the page, followed by the recognised phonetic alphabet for that letter, followed by the Morse Code for the letter. For the full alpabet and pronunciation key see: Phonetic Alphabet appendix page.
Photovoltaic Cell.
Aa wafer of semiconductor material that produces electricity when light shines on it. Sometimes called a solar cell. Each cell produces about one-half volt when fully illuminated. Cells are connected in series to increase the voltage. The size or surface area of the cell determines the maximum current that the cell can supply. An array of cells forms a solar panel that can be used to charge a rechargeable battery or power low consumption equipment.
Photovoltaic Conversion.
The process by which a semiconductor PN junction changes sunlight directly into energy.
Pico.
The metric
prefix for 10-12, or divide by 1,000,000,000,000.
Picket Fencing.
Originally an American term, if a repeater user's signal isn't strong enough to maintain solid access to the machine's input (such as when operating from a vehicle passing beneath underpasses or through hilly terrain), the signal would be hard to copy because of a pronounced, rapid fluttery or choppy characteristic. It sounds as if the transmitting station is passing behind a picket fence that alternately blocks and passes its signals. Picket fencing usually ceases when the transmitting station moves closer to the repeater or into a clearer location.
A Coax connector commonly used with HF, VHF & some UHF equipment. Invented in the 1930's by an Amphenol engineer named E. Clark Quackenbush. Its female type is called SO239. See also: Fitting a PL259.
A transistor that has a layer of N-type semiconductor material sandwiched between layers of P-type semiconductor material.
Polarization.
The electrical-field characteristic of a radio wave. An antenna that is parallel to the surface of the earth, such as a dipole, produces horizontally polarized waves. One that is perpendicular to the earth's surface, such as a quarter-wave vertical, produces vertically polarized waves. An antenna that has both horizontal and vertical polarization is said to be circularly polarized.
Portable.
1. A portable station is one that is designed to be easily moved from place to place but can only be used while stopped. Portable operation is away from the home base station. (see also, Mobile).
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2. You may hear a station <callsign>/P or Portable when using a handheld radio. This is, in fact, incorrect! <callsign>/P should only be used if the Licensee is at a Temporary Location with equipment that can only be used while stopped. Handeld radios are 'covered' by <callsign>/M or Mobile.
Portable Device.
A radio transmitting device designed to have a transmitting antenna that is generally within 20 centimeters of a human body.
Positive Offset.
The repeater's input frequency is higher than the output frequency.
Potentiometer.
Another name for a variable resistor. The value of a potentiometer can be changed over a range of values without removing it from a circuit.
Power.
The rate of energy consumption. We calculate power in an electrical circuit by multiplying the voltage applied to the circuit times the current through the circuit (P = I×V).
Power Amplifier (PA).
The final output stage of a transmitter.
Power Density.
A measure of the power flow through a unit area perpendicular to the direction of propagation. It is usually expressed in watts per square meter (W/m2).
Power Supply.
A circuit that provides smooth, regulated direct current (DC) output at some desired voltage and current from an AC input voltage for powering devices that would otherwise require batteries.
Pre-Amplifier (Preamp).
A circuit that amplifies the received signal before it enters the main radio circuitry. May be built into the radio, a table top device or mounted close to the antenna (mast head).
Primary Winding.
The coil in a transformer that is connected to the energy source.
Priority Traffic.
Emergency-related messages, but not as important as Emergency Traffic.
Priority Watch.
Reception mode, which by a selected frequency is always periodically, checked when the VFO is set to a different frequency.
Procedural Signal (Prosign).
One or two letters sent as a single character. Amateurs use prosigns in CW contacts as a short way to indicate the operator's intention. An example is K for "Go Ahead,".
Product Detector.
A device that allows a receiver to process CW and SSB signals.
Project 25 (P25).
A set of standards produced through the joint efforts of the Association of Public Safety Communications Officials International (APCO), the National Association of State Telecommunications Directors (NASTD), selected Federal Agencies and the National Communications System (NCS), and standardized under the Telecommunications Industry Association (TIA). P25 is an open architecture, user driven suite of system standards that define digital radio communications system architectures capable of serving the needs of Public Safety and Government organizations. See also: Project 25 in depth in the Appendix & the Digital Modes page.
The main earthing terminal of a PME installation is connected to the neutral of the electricity supply. All metallic surfaces within the building are bonded together at the consumer unit ('fuse box'). This gives the consumer an earth of very high reliability and of low impedance. Under very rare fault conditions a high potential may appear which could rise to 240V between electrical ground and any added RF ground. Read Protective Multiple Earthing (PME) - Advice for radio amateurs from the RSGB for further information (requires Adobe Reader ).
Protocol.
A set of standardised procedures for transmitting or storing data, especially those used in regulating data transmission between computers or peripherals. See also: Digital Modes page.
Digital mode that combines the advantages of a simple variable length text code with a narrow bandwidth phase-shift keying (PSK) signal using DSP techniques. This mode is designed for 'real time' keyboard operation and at a 31 baud rate is only fast enough to keep up with the typical amateur typist. See also: Digital Modes page.
The output from a rectifier before it is filtered. The polarity of a pulsating dc source does not change, but the amplitude of the voltage changes with time.
Push / Press To Talk (PTT).
The button or bar on the side of the microphone, or handheld transceiver, that switches the transceiver into transmit mode when pushed or pressed.
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