Re: [SDRSharp] Re: From a SDR Grapevine...

Alberto I2PHD

On 8/14/2013 7:59 PM, josephrot wrote:

Next time, please fine all terms at their first use, or what the acronyms / abbreviations mean,
and a great many others could follow your writings and answers.

Oh, sorry... I had given for granted that those acronyms were more or less known as they
are used very often in the SDR field, but maybe I was wrong.

So, here it comes an attempt to a short explanation. A longer and more complete one can
of course be found using Wikipedia,

SDR� - Need this to be explained ?� Software Defined Radio, a technology where the working
��������� of the radio is mostly defined by a software program, and in a lesser extent by hardware.

ADC� - Analog to Digital Converter. Usually a single chip that converts a signal from an analog
��������� form to a numeric one, in equally time-spaced samples, and quantized in amplitude
��������� with a number of bits depending on the specific chip (usually from 8 to 24).

FPGA - Field Programmable Array. A chip containing hundreds of thousands of uncommitted
��������� logic circuits, that can be dynamically reconfigured to perform the specific function(s)
��������� needed for the specific application,

DDC� - Digital Down Converter. Usually one of the functions programmed into an FPGA. A DDC
��������� implements the functions of downconversion and downsampling as described in my previous
������� � message.

NCO -� Numerically Controlled Oscillator. An algorithm that behaves as a hardware oscillator,
��������� but whose output is a series of numbers that are the samples of the signal that
��������� is generated (usually a sine wave).

CIC� - Cascaded Integrator Comb. Also implemented inside the FPGA. An interesting algorithm
�������� described about 25 years ago by Hogenauer, that implements the low pass filtering
�������� needed before the downsampling stage. Loved by FPGA programmers, as it can be
�������� implemented without using multiplicators, a scarce resource in an FPGA.

FIR� - Finite Impulse Response filter.� A kind of filter that can be used to implement low pass, high
�������� pass, band pass, all pass functions. A somewhat related kind of filters are the IIR, Infinite
�������� Response Filter. It would take too much space to describe here the differences, the pros and cons.

FFT - Fast Fourier Transform. The king (or the queen ?) of the algorithms used in the SDR field.
� � � �� Described for the first time in the early sixties of last century by Cooley and Tukey, two
�������� respected mathematicians of the time. The FFT transforms the time representation of
� � � �� a signal into its frequency representation (and viceversa). Quite useful to perform
�������� filtering, to compute spectrum, waterfall and a lot of other functions.

DUC - Digital Up Converter. Basically the opposite a a DDC. An algorithm that upsamples and
�������� upconverts a baseband signal to the final output frequency. Normally followed by a DAC.

DAC - Digital to Analog Converter. The opposite of an ADC. A piece of hardware that takes as its
�������� input a series of numbers that represent the signal to be generated, and that outputs
�������� the analog signal described by those numbers. Needs to be followed by an anti-alias filter.

Hope to not have forgotten some acronyms...

73 Alberto I2PHD

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