R - Romeo - di-dah-dit
RAAG.
RAC.
Radio Amateurs of Canada, a national amateur radio organization in Canada.
RAL.
Radio Amateurs of Lebanon, a national amateur radio organization in the Lebanese Republic.
Radiation Pattern.
Commonly refers to the directional (angular) dependence of radiation from the antenna.
Radio Direction Finding (RDF).
The 'art' of tracking down a transmitter, or a series of transmitters, often called a 'Fox Hunt'.
Radio Frequency (RF).
Radio Frequency, emissions in the radio portion of the electromagnetic spectrum, that is from 10kHz to 300GHz. In common usage it is shortened to 'RF'.
Radio Frequency Interference (RFI).
Disturbance to electronic equipment caused by radio-frequency signals.
Radio Licence.
Radio Propagation.
The term used to explain how radio waves behave when they are transmitted, or are propagated from one point on the Earth to another.
Radioteletype (RTTY).
Radio signals sent from one teleprinter machine to another machine. Anything that one operator types on his teleprinter will be printed on the other machine. Also known as narrow-band direct-printing telegraphy.
See also: Digital Modes page.
Rally.
A gathering usually sponsored by a Amateur Radio Club. A basic rally is a flea market of used Radio equipment and parts that Amateur Radio Operators may wish to buy or sell. A more elaborate rally may include new equipment dealers and manufacturers, seminars, Radio events. Most events also provide some sort of refreshments and are always a good place for Amateur Radio Operators to meet other Amateurs that they may have only previously met over the air. A small fee is often charged for entry to a rally and this usually goes to help the sponsoring club pay for club equipment and other operating expenses.
Random-Length Wire Antenna (Long Wire Antenna).
A multiband antenna consisting of any convenient length of wire and an Antenna Tuning Unit, usually without the use of feed line.
RDF.
Reactance.
The opposition to current flow created by a capacitor or an inductor in an AC circuit. Reactance is measured in Ohms.
Reactance Modulator.
An electronic circuit whose capacitance or inductance changes in response to an audio input signal.
Receiver.
A device that converts radio waves into signals we can hear or see.
Receiver Incremental Tuning (RIT).
A transceiver control that allows for a slight change in the receiver frequency without changing the transmitter frequency. Some manufacturers call this a clarifier (CLAR) control.
Receiver Overload.
Interference to a receiver caused by a strong RF signal that forces its way into the equipment. A signal that overloads the receiver's RF amplifier (front end) causes front-end overload. Receiver overload is sometimes called RF overload.
Rectifier / Rectifier Diode.
An electronic component that allows current to pass through it only in one direction. This type of diode can handle higher powers and voltages than a signal diode and is commonly used to rectify AC to DC in power supplies.
Reed-Solomon.
An error-correcting code that works by sampling the data from a mathematical formula that is created from the data itself. This data is over-sampled i.e. sampled at significantly higher than twice the bandwidth. By sampling much more than is necessary, there is greater confidence that the results from the mathematical formula are consistent and accurate. If data is missing or corrupted then it is possible to reconstruct the original data from the extra information resulting from the over-sampling. Reed-Solomon coding is used extensively in products such as CD’s and DVD’s, in ADSL technologies, in digital radio modes such as CLOVER and in digital television broadcasting using satellite, cable and freeview.
See also: Digital Modes page.
Reflected Power.
Non-radiated power dissipated as heat when the transmitter is mismatched to the antenna or load.
Reflection.
Signals that travel by line-of-sight propagation are reflected by large objects like buildings.
Reflector.
An element behind the driven element in a Yagi and some other directional antennas.
Refract / Refraction.
To bend. Electromagnetic energy is refracted when it passes through a boundary between different types of material. Light is refracted as it travels from air into water or from water into air.
Repeater / Repeater Station.
Listens on one frequency and automatically retransmits what it hears on another frequency. By locating repeaters at high locations, Amateur Radio Operators can talk to other Amateurs over greater distances than they normally could. These repeaters are usually used on the VHF or UHF Amateur bands and almost always operate by way of Frequency Modulation.
See also: Repeaters Explained.
Resistance.
The ability to oppose an electric current.
Resistor.
Any material that opposes a current in an electrical circuit. An electronic component specifically designed to oppose or control current through a circuit, usually dissapating the 'loss' as heat.
Resonance.
1, Resonance of a circuit involving capacitors and inductors occurs because the collapsing magnetic field of the inductor generates an electric current in its windings that charges the capacitor, and then the discharging capacitor provides an electric current that builds the magnetic field in the inductor, and the process is repeated continually.
.
2, Antenna resonance is the frequency that the antenna was designed to operate (or resonate) on.
Resonant Frequency.
The desired operating frequency of a tuned circuit. In an antenna, the resonant frequency is one where the feed-point impedance contains only resistance.
RF.
RF Burn.
A burn produced by coming in contact with exposed RF voltages.
RF Carrier.
A steady radio frequency signal that is modulated to add an information signal to be transmitted. For example, a voice signal is added to the RF carrier to produce a voice transmission.
RF Choke.
An inductor designed to have a high reactance to a particular frequency when used in a signal-carrying circuit. Chokes depend upon the property of self-inductance for their operation. Common-mode choke coils are useful in a wide range of prevention of electromagnetic interference (EMI) and radio frequency interference (RFI) from power supply lines and for prevention of malfunctioning of electronic equipment.
RF Envelope.
The shape of an RF signal as viewed on a oscilloscope.
RF Ground.
Connection of amateur equipment to earth ground to eliminate hazards from RF exposure and reduce RFI.
RFI.
RF Overload.
RF Radiation.
Waves of electric and magnetic energy. Such electromagnetic radiation with frequencies as low as 3 kHz and as high as 300 GHz are considered to be part of the RF region.
RF Safety.
Preventing injury or illness to humans from the effects of radio-frequency energy.
Rig.
The radio amateur's term for a transmitter, receiver or transceiver.
Ripple.
The amount of change between the maximum voltage and the minimum voltage in a pulsating dc wave form.
RIT.
RMS.
Root-Mean Square (RMS) Voltage.
Another name for effective voltage. RMS is calculated as 0.707 times the peak value, or 1.414 times the RMS voltage gives you the peak value.
Rotator.
Device used to remotely and electrically rotate a beam or dish antenna. Some types also alter the vertical angle (azimuth) for EME or satellite working, where the height above the horizion is varied and critical.
RSGB.
Radio Society of Great Britain, the national amateur radio organization in the UK.
RST.
A system of numbers used for signal reports: R is readability, S is strength and T is tone.(On telephony, only R and S reports are used).
See also: RST codes page.
RTTY.
Rubber Duck.
Slang term for a rubber covered flexible antenna, usually helically wound, used on handheld transceivers.
RX.
Short hand for receive, received or receiver.