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8/9/2019 Band-Pass Filter on GNU Radio
1/11
2015
Author: Rakesh
Email id: [email protected]
Implementation of Band-Pass filter
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What is Gnu radio?
GNU Radio is a software library, which can be used to develop complete applications for
radio engineering and signal processing.
Introduction
GNU Radio is a free and open-source software development toolkit that provides
signal processing blocks to implement software radios. It can be used with readily-
available low-cost eternal R! hardware to create software-defined radios, or without
hardware in a simulation-like environment.
GNU Radio is licensed under the GNU General "ublic #icense $G"#% version &. 'll ofthe code is copyright of the !ree (oftware !oundation. )hile all the applications are
implemented using python language while critical signal processing path is done using
*++ language.
Idea behind GNURADIO
he goal is to give ordinary software people the ability to hack the electromagnetic
spectrum, i.e. to understand the radio spectrum and think of clever ways to use it.
Wh GNURADIO
Instead of purchasing multiple epensive radios, a single generic radio can be
implemented using GNU Radio software and with support of minimal hardware to
receive and transmit processed signal at reuired freuencies and any data type can be
passed from one block to another i.e.it can be in bits, bytes, vectors, bursts or more
comple data types
(ince the performance critical blocks are implemented in *++ using processor floating
point etensions the developers are able to implement real-time, high-throughput radio
systems in a simple-to-use, rapid-application-development environment.
/01&, (hree #akshmi *omple, 2nd !loor, 3pp. o 4ivekananda "ark, Girinagar, 5angalore - 678896.
"h. No: 898-27;22;27, )ebsite:www.tenettech.com,
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3ne can use it to write applications to receive data out of digital streams or to send data
into digital streams, which is then transmitted using hardware. GNU Radio has filters,
channel codes, synchronisation elements, euali>ers, demodulators, vocoders, decoders,
and many other elements which are called as blocks that are typically found in radio
systems.
!eatures
he main features of GNU Radio are fle!ibilitand confi"urabilit#
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What is Band-Pass filter?
' 5and-"ass filter is a device that passes freuencieswithin a certain range and re?ects
$attenuates% freuencies outside that range.
'n eample of an analogue electronic 5and-"ass filter is an R#* circuit $a resistor@inductor@
capacitor circuit%. hese filters can also be created by combining a #ow-"ass filter with a high-
pass filter. 5and-"ass is an ad?ective that describes a type of filter or filtering processA it is to be
distinguished from pass-band, which refers to the actual portion of affected spectrum. Bence, one
might say C' dual 5and-"ass filter has two pass-bandsC. ' 5and-"ass signal is a signal
containing a band of freuencies not ad?acent to >ero freuency, such as a signal that comes out
of a 5and-"ass filter.
'n ideal 5and-"ass filter would have a completely flat pass-band $e.g. with no gain1attenuation
throughout% and would completely attenuate all freuencies outside the pass-band. 'dditionally,
the transition out of the pass-band would be instantaneous in freuency. In practice, no 5and-
"ass filter is ideal. he filter does not attenuate all freuencies outside the desired freuency
range completelyA in particular, there is a region ?ust outside the intended pass-band where
freuencies are attenuated, but not re?ected. his is known as the filter roll-off, and it is usually
epressed in d5 of attenuation per octave or decade of freuency. Generally, the design of a filter
seeks to make the roll-off as narrow as possible, thus allowing the filter to perform as close as
possible to its intended design. 3ften, this is achieved at the epense of pass-band or stop-band
ripple.
he bandwidth of the filter is simply the difference between the upper and lower cutoff
freuencies. he shape factor is the ratio of bandwidths measured using two different attenuation
values to determine the cutoff freuency, e.g., a shape factor of 2:D at &81& d5 means the
bandwidth measured between freuencies at &8 d5 attenuation is twice that measured between
freuencies at & d5 attenuation.
3ptical 5and-"ass filters are common in photography and theatre lighting work. hese filters
take the form of a transparent colored film or sheet.
5and-"ass filters are widely used in wireless transmitters and receivers. he main function of
such a filter in a transmitter is to limit the bandwidth of the output signal to the band allocated
/01&, (hree #akshmi *omple, 2nd !loor, 3pp. o 4ivekananda "ark, Girinagar, 5angalore - 678896.
"h. No: 898-27;22;27, )ebsite:www.tenettech.com,
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for the transmission. his prevents the transmitter from interfering with other stations. In a
receiver, a 5and-"ass filter allows signals within a selected range of freuencies to be heard or
decoded, while preventing signals at unwanted freuencies from getting through. ' 5and-"ass
filter also optimi>es the signal-to-noise ratio and sensitivity of a receiver.
/01&, (hree #akshmi *omple, 2nd !loor, 3pp. o 4ivekananda "ark, Girinagar, 5angalore - 678896.
"h. No: 898-27;22;27, )ebsite:www.tenettech.com,
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D% 5and-"ass filter
he GNU Radio *ompanion with basic blocks $3ptions block and 4ariable block%
Options bloc$defines the IE, itle and Eescription of the eperiment.
/01&, (hree #akshmi *omple, 2nd !loor, 3pp. o 4ivekananda "ark, Girinagar, 5angalore - 678896.
"h. No: 898-27;22;27, )ebsite:www.tenettech.com,
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%ariable Bloc$defines to declare variables globally. his block maps a value to a uniue
variable. his variable block has no graphical representation. he variable can be referenced
$by IE% from other blocks in the flowgraph.
o IE F samprate
o 4alue F &2888B>
&i"nal sourceis a wave form genrator. 4ery first block genrates the sine wave, second block
genrates the suare wave, third block genrates triangler wave and finaly fourth block genrates the
sawtooth waveform.
o IE:analogsigsource8
o 3utput type: float
o !re: D08B>
o 'mplitude: D4
/01&, (hree #akshmi *omple, 2nd !loor, 3pp. o 4ivekananda "ark, Girinagar, 5angalore - 678896.
"h. No: 898-27;22;27, )ebsite:www.tenettech.com,
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Band-Pass filter' this filter is a convenience wrapper for an fir filter. (ample rate, cutoff
freency and transition width are in Bert>.
IE: bandpassfilter8
ype: float
#ow cutoff fre: 288B>
Bigh cutoff fre: 988B>
(hrottel bloc$: hrottel is a device that control the flow of samples such that average rate doesnot eceeds samples1sec.hrottle is used because no hardware interface has done.
o IE: blocksthrottel
o ype: float
o 4ec length: D
/01&, (hree #akshmi *omple, 2nd !loor, 3pp. o 4ivekananda "ark, Girinagar, 5angalore - 678896.
"h. No: 898-27;22;27, )ebsite:www.tenettech.com,
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W) GUI scope sin$'he )H GUI (cope sink is the destination block of the flow chart. his
block is used to view the time domain representation of the output. he simulation output of
the received signal is seen with this block.
o IE: wguiscopesink28
o ype: float
/01&, (hree #akshmi *omple, 2nd !loor, 3pp. o 4ivekananda "ark, Girinagar, 5angalore - 678896.
"h. No: 898-27;22;27, )ebsite:www.tenettech.com,
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/01&, (hree #akshmi *omple, 2nd !loor, 3pp. o 4ivekananda "ark, Girinagar, 5angalore - 678896.
"h. No: 898-27;22;27, )ebsite:www.tenettech.com,