A/D Converter = The conversion of analog signals to a digital data stream for DSP.  In a transmitting application the process is reversed by a D/A converter that converts a digital data stream to an analog signal.

Baseband = the frequency domain where Digital Signal Processing is accomplished.  Frequencies at or near “0” Hz.

D/A Converter = The complement of an A/D Converter.  See A/D Converter.

Direct Conversion = a radio frequency conversion process where the RF signal is translated directly to baseband (receiver) or translated directly from baseband (transmitter).  Baseband is the domain digital signal processing.  Direct conversion is one example of digital down conversion (receiver) and digital up conversion (transmitter).

DDC =Digital down conversion, an SDR receiving process

DSP = Digital Signal Processing

DUC = Digital up conversion, an SDR transmitting process

Euler Complex Exponential = a mathematical function that permits I and Q signal processing.   This function is at the heart of modern DSP software

Flow graph = The graphical representation of any DSP process rendered by GRC

FPGA = Field programmable gate array.  An integrated circuit with logic gates that are programmed with firmware, rather than software.  For a receiving SDR application the FPGA provides an initial level of DSP to manage the massive data output from the A/D converter.  The DSP process in the FPGA simplifies the subsequent DSP operations by the host computer.  DSP is streamlined vastly improving ‘real time’ radio performance.

GNU Radio = an open source DSP library for both DSP simulation and operational radio applications

GPIO – General purpose input and output connections from a computer controlled system

GRC = GNU Radio Companion, the graphical programming interface automatically built into the GNU Radio application.  GRC enables DSP programming by interconnecting graphical blocks as different from line commands.

GUI = Graphical User Interface, the schematic representation on the computer screen

and Q = In phase and out of phase signals or digital data streams.  The I and Q signals or I and Q data streams contain the exact same frequency, information but each signal is offset from the other by a 90 degree phase difference.  The 90 degree phase difference represents an offset of 1/4 of a cycle.

NCO = Numerically Controlled Oscillator implemented in the FPGA.  Can be tuned separately with appropriate frequency commands.

Operating GUI = The graphical display that appears when a GNU Radio flow graph is executed.  The operating GUI permits display and control of DSP operation by the user.

Python = a high level software programming language.  Python is the bridge between the graphical programming interface of GNU Radio and the low level ‘C’ language of an executed GNU Radio application.

Quadrature – another term used to describe I and Q signals, signals that are 90 degrees out of phase to one another or “in Quadrature”.

RF = Radio Frequency refers to signals received and transmitted by real radios

RFIC = Radio Frequency Integrated Circuit.  An analog transceiver front end for a modern SDR.  Extends the high frequency range of the SDR to VHF and Microwave frequencies.

RTL SDR = Also known as the “RTL Dongle”.  A second generation SDR receiver that does not incorporate FPGA technology.  Not “state of the art” hardware.  Extremely useful for many SDR receive applications.

SDR = Software Defined Radio.  A radio system where significant portions of the signal processing is accomplished by Digital Signal Processing

Sinusoid = Sine wave with modulation.  For example an RF carrier with FM modulation is a sinusoid.

UHD = Universal Hardware Driver.  The data interface between a USRP and DSP platform.

USRP = Universal Software Radio Peripheral.  Originally a trade term applied to SDR hardware produced by Ettus Research.  The term artfully emphasized the software defining role of this class of radio, relegating the hardware to the status of a generic ‘peripheral’.  Now USRP has become a generic designation for any advanced SDR that with UHD are compatible with a wide range of DSP software.

Widget = A term applied to a software tool represented as an icon.  Widgets can implement control tools in the operating GUI.

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