Software Defined Radio

Software Defined Radio 

Part 1

SDR is Software defined Radio is used for the to Capturing and analyzing the various radio frequency signals , we can monitor and transmit the signals also , according to security reasons i am not showing transmission of open source signals but soon i will update how to pentest the replay attacks of key fobs and smart door lock systems.

what we going to discuss

1. Introduction about Radio And Software Defined Radio
2. Various types of devices
3. Antennas
4. Radio waves
5. Capturing the FM Signals And Analyzing


1. Software Defined Radio (SDR)
2. Antenna
3. GQRX software for Linux , windows - SDR software
4. Gnu Radio Companion
5. Computer


Radio is the technology of using radio waves to carry information, such as sound, by systematically modulating some property of electromagnetic energy waves transmitted through space, such as their amplitude, frequency, phase, or pulse width.(Wikipedia)

Software Defined Radio (SDR):
Radio communication system where components that have been typically implemented in hardware (e.g. mixers, filters, amplifiers, modulators/demodulators, detectors, etc.) are
instead implemented by means of software on a personal computer or embedded system.(Wikipedia)

Some other different SDR Devices for testing radio signals

1. AirSpy

An antenna , or aerial, is an electrical device which converts electric power into radio waves, and vice versa.It is usually used with a radio transmitter or radio receiver. (wikipedia)

Types of antennas..
1. Wire Antennas
2. Travelling Wave Antennas
3. Reflector Antennas
4. Microstrip Antennas
5. Log-Periodic Antennas
6. Aperture Antennas

Radio Waves
Radio waves are a type of electromagnetic radiation with wavelengths in the electromagnetic spectrum longer than infrared light. Radio waves have frequencies as high as 300 GHz to as low as 3 kHz, though some definitions describe waves above 1 or 3 GHz as microwaves, or include waves of any lower frequency. At 300 GHz, the corresponding wavelength is 1 mm (0.039 in), and at 3 kHz is 100 km (62 mi). Like all other electromagnetic waves, they travel at the speed of light. Naturally occurring radio waves are generated by lightning, or by astronomical objects.(Wikipedia)

Analyzing FM Signals:

Connect SDR To Computer as shown below

And Connect Discone Antenna , here we are using Discone antenna
To get more signal radius of long distances. specially people will use parabolic antennas to get long distance radio signals practically proved already 

After connecting SDR , Run the gqrx and set the appropriate frequency for the testing the FM Signal Example: 93.5mhz
Features of gqrx
    .. Discover devices attached to the computer.
    .. Process I/Q data from the supported devices.
    .. Change frequency, gain and apply various corrections (frequency, I/Q balance).
    .. AM, SSB, CW, FM-N and FM-W (mono and stereo) demodulators.
    .. Special FM mode for NOAA APT.
    .. Variable band pass filter.
    .. AGC, squelch and noise blankers.
    .. FFT plot and waterfall.
    .. Record and playback audio to / from WAV file.
    .. Record and playback raw baseband data.
    .. Spectrum analyzer mode where all signal processing is disabled.

Here we can observe in that particular frequency range there thick line visible , it means the radio wave consists the audio

Gnuradio is written in Python and it is using for Signal processing and without hardware in a simulation-like environment. It is widely used in hobbyist, academic, and commercial environments to support both wireless communications research and real-world radio systems.

Download from here

To Install Gnuradio in Ubuntu follow the command
#sudo apt install gnuradio-companion

To Analyze the FM Signal with Gnuradio , download and open with gnuradio-companion

And set the frequency in Wx gui as shown below and click on run

The Fast Fourier Transform (FFT) is simply a fast (computationally efficient) way to calculate the Discrete Fourier Transform (DFT).

Fourier analysis converts a signal from its original domain (often time or space) to a representation in the frequency domain and vice versa.

Here we can see in FFT Plot (Fast Fourier transform) shown below

A waterfall plot is a three-dimensional plot in which multiple curves of data, typically spectra, are displayed simultaneously.
And here it is waterfall plot Image

What we did in this part its just a ordinary FM Stationary Signals analyzing so this is not much interesting for next signal analyzing module a bit interesting to coma


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