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Regulator : A device - often built to employ a Zener Diode as reference - which maintains a constant output voltage over a range of load currents and input voltages.

Repeater : A transceiver - often comprised of separate transmitted and receiver linked by controlling hardware. A repeater picks up a radio signal and re-transmits it, allowing weak stations to be heard from further away than normally possible.

Repeater council : A voluntary regional amateur organisation coordinating repeater frequency pair assignments to minimise interference. As no individual amateur group owns any given radio frequency, a council does not exercise legal authority to force individual repeater operators onto a specific frequency, height, location, power or directional pattern. Nonetheless, amateurs are obligated by national laws to avoid interference to other amateur stations and official regulatory agencies will resolve interference complaints between repeater operators by forcing uncoordinated repeaters to move off frequencies where their operation interferes with any coordinated repeater.

Resistance : The measure of how much an object (a resistor) opposes the flow of electric current.

Resistivity : The measure of how strongly a material (eg plastic) opposes the flow of electric current.

Resistor : A device that opposes the flow of electric current.

RFI : Radio Frequency Interference (also BCI - broadcast interference, TVI - television interference). Normally resolved by installation of filters at the transmitter, the affected receiver(s) or both.

Ripple : The residual AC left over after rectification and filtering when an AC supply has been converted to DC'

RIT : Receive Incremental Tuning, Receive Independant of Transmit. The ability to shift the receive frequency of a transceiver away from the transmit frequency by a small amount.

RMS : Root Mean Square. Calculated by squaring each of the values on a signal, calculating the mean of the squares, and then taking the square root of the mean. approximately 0.707 of the peak value.

ROS Digital : An MFSK digital mode created in 2009.

RSGB : Radio Society of Great Britain - national amateur radio organisation of UK.

RSQ code Used to describe the readability, strength and quality of digital modes.

RST code Used to describe the readability, strength and tone of voice or CW transmissions.

RTTY : Radioteletype.

RSV code used to describe the readability, stength and video quality of SSTV transmissions

RX : Abbreviation for receive or receiver