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User’s Manual

Version 0.3.0

Gonzalo José Carracedo Carballal

June 27, 2022

Содержание SigDigger

Страница 1: ...User s Manual Version 0 3 0 Gonzalo Jos Carracedo Carballal June 27 2022...

Страница 2: ......

Страница 3: ...ew 13 Con guring the signal source 14 SDR device 15 File source 16 Source parameters 17 Starting a capture 18 Real time source tweaks 22 Adjusting the FFT 24 Listening to the radio audio preview 26 De...

Страница 4: ...s 49 DSP chain 49 Inspection tabs 52 Using the Generic Channel Inspector tab 52 Spectrum sources 55 Fine tuning 56 Parameter estimation 57 Demodulator controls 59 Data forwarding 62 5 Panoramic spectr...

Страница 5: ...R2 support library It also supports record and playback of RF IF sample data to and from multiple le formats including WAV and raw complex oat I Q In addition to the reverse engineering related featur...

Страница 6: ...ith a back ground in cybersecurity mathematical engineering and astrophysics He has been in love with radio and radioastronomy since he rst watched Contact8 circa 1997 He likes coding for fun in his s...

Страница 7: ...ained executables and therefore easy to run Open a terminal change to the directory in which the AppImage le was downloaded and give execute permissions to it this is something that needs to be done o...

Страница 8: ...xist in the form of a redistributable ZIP le containing the main SigDigger executable along with all its dependencies This build was possible thanks to ngel Fern ndez4 who managed to port most of the...

Страница 9: ...is hard It is hard because it involves multiple threads using the corresponding implementation of poll that works for each possible subset of objects If you are interested in this subject and want to...

Страница 10: ...ays to compile SigDigger Fully automated build using BLSD GNU Linux only BLSD short for Build Latest SigDigger from Develop is a shell script that builds SigDigger from development branch and installs...

Страница 11: ...one from master run git clone https github com BatchDrake sigutils git clone https github com BatchDrake suscan git clone https github com BatchDrake SuWidget git clone https github com BatchDrake Sig...

Страница 12: ...this works for many users you may need to update your environment variables for the previous commands to work export LD_LIBRARY_PATH usr local lib LD_LIBRARY_PATH export PKG_CONFIG_PATH usr local lib...

Страница 13: ...omewhat excessive detail all the necessary steps to arrive to at least the rst use case At the end of this chapter you will nd that most of the time these steps need to be followed only once Interface...

Страница 14: ...gnal source used to perform different adjustments to the signal source in real time Inspection used to inspect the contents of the selected channel in different ways and FFT used to adjust different p...

Страница 15: ...o make copies of it with different names Save as and overwrite it with the contents of existing pro les Load profile We usually start by de ning the physical origin of the signal source This is done b...

Страница 16: ...ly from the con gured sample rate although this can be adjusted The Loop check box is used to inform SigDigger whether the le source should be rewound to its start once the playback hits the end Many...

Страница 17: ...t the second most important parameter you need to provide is the sample rate The sample rate is a fundamental parameter that determines both how fast signal data is consumed by SigDigger and the frequ...

Страница 18: ...LNBs The sign of this frequency must be positive for downconverters and negative for upconverters Decimation De nes sample averaging Useful for SDR receivers with poor ADC resolution A decimation of N...

Страница 19: ...demodulator frequency The latter can be used to de ne the central frequency of a channel we want to analyze The numbers between the spectrum and the waterfall are referred as the frequency axis Scroll...

Страница 20: ...ere f is the frequency of the spectrum bin in Hz xk is the k th sample in the FFT buffer wk is the k th sample of the window function buffer fs the sample rate and N the FFT buffer size U is certain c...

Страница 21: ...gaussian distribution with a variance that does not depend on the sample rate and is only proportional to the signal power which would require a 1 N scaling to keep the spectrum oor in the same level...

Страница 22: ...tab Other parameters you can tweak are Swap I Q toggles I Q swapping i e assumes that the I channel has Q data an vice versa This has the effect of mirroring the spectrum 9 Hardware AGC toggles receiv...

Страница 23: ...capture les will be saved Capture les are stored in Complex 32 bit oat format exactly as in Gqrx and named according to this pattern10 sigdigger_YYYYMMDD_hhmmssZ_SampleRate_Frequency_float32_iq raw As...

Страница 24: ...e next Note that higher FFT sizes imply longer ll up times for the FFT buffer blurring the waterfall vertically An increase in FFT resolution is always achieved at the expense of time resolution It al...

Страница 25: ...dates Useful when the vertical zoom is high and you want to spot wide and weak signals Spect Wf controls the relative propotion of window space used by both the spectrum and waterfall Detect enables p...

Страница 26: ...mple let s try to listen to an FM broadcast We will be assuming that you have plugged an SDR receiver to 12 SSB stands for Single Side Band an umbrella term for two complementary modulation types LSB...

Страница 27: ...increase them little by little until the vertical distance between any signals and the noise oor does not increase anymore When this happens you usually have reached the maximum signal to noise ratio...

Страница 28: ...you adjust other audio related parameters such as Squelch level SQL if enabled informs SigDigger the signal level below which audio preview should be automatically muted How squelch is performed de pe...

Страница 29: ...it is limited by the bandwidth17 of the selected channel Higher sample rates imply more room for higher audio quality which is ultimately governed by the signal s quality and the cutoff of the audio l...

Страница 30: ...ow and the naming pattern audio Modulation Frequency Rate NNNN wav With Modulation being the modulation type FM AM LSB USB Frequency the channel s center frequency Rate the sample rate used for the au...

Страница 31: ...of a generic demodulator Both work ows can be accessed through the side panel s Inspection tab SigDigger relies on suscan for channelization which in turn relies on the Fast Fourier Transform to both...

Страница 32: ...psk fsk audio and raw If the inspector has a demodulation stage the demodulated output can be used to fed another in spector thus enabling subcarrier inspector like RDS in FM broadcasts or APT Deferr...

Страница 33: ...ane with the I component displayed in the horizontal axis and the Q component in the vertical axis If a selection is present the most recent samples are represented The numbers on the right represent...

Страница 34: ...capture is triggered automatically based on the SNR Several controls in the Inspection group affect how the Autosquelch feature should behave Trigger SNR speci es the signal level with respect to the...

Страница 35: ...y It is recommended to disable Waveform for better visualization of the phase frequency information Phase coloring is inspired in the historical PAL3 color wheel in which the phase information of the...

Страница 36: ...g the full capture is displayed This information includes Sample rate decimated sample rate of the channel used for capture Duration length in time units of the captured waveform Length length in samp...

Страница 37: ...sample number The Fine tune selection controls allow ad justing the selection limits in one sample increments and one selection length increments The Lock button locks the selection start and end eff...

Страница 38: ...le of the symbol rate which is usually the case selecting only one symbol to guess the symbol rate from the Selection freq will result in a somewhat inaccurate measurement The following example illust...

Страница 39: ...ull capture can be saved to a le Three le formats are supported WAV regular WAV le with I Q components stored in the stereo channels MATLAB Octave script and MATLAB 5 0 MAT le The MATLAB Octave script...

Страница 40: ...tone used to provided an absolute phase reference This is the case for PAL signals and certain PSK signals Unless the phase is stabilized i e the residual frequency of the signal is zero we cannot mak...

Страница 41: ...ided by the selection It its com pletely ignorant of the underlying modulation In most cases this operation should be complemented with a Manual frequency correction adjusting both the Frequency and P...

Страница 42: ...nalysis Multiplies each sample by the conjugate of the pre vious This results in a periodic phase shift that can be used to measure the symbol rate of phase modulated transmissions Quadrature demodula...

Страница 43: ...information in the form of symbols From this page you can set which variable of the signal you want to sample its Amplitude Phase or Frequency whether you want to restrict the Sampling interval to th...

Страница 44: ...at despite the obvious frequency structure of this burst we were not sure whether this was a frequency modulated signal or an amplitude modulated signal We start by selecting the burst with the mouse...

Страница 45: ...duce the symbol timing Manual we provide the symbol rate manually using the Symbol rate spin box Only useful for short bursts or signals with a very precise clock reference7 Fixed interval partition i...

Страница 46: ...y transitions we measured a symbol rate bit rate of 1000 bps Since this is a frequency modulated signal we choose Frequency in the Decision space box As we tted the periodic selection intervals to the...

Страница 47: ...enter of the leftmost peak to the rightmost peak This is used to adjust the decision intervals to the right values and it is mandatory for signals with more than 1 bit per symbol Click the histogram w...

Страница 48: ...pboard Symbols are copied as a sequence of digits being 0 the lowest symbol in this case the lowest frequency and 2M 1 the highest symbol 1 for binary modulations 3 if every symbol encodes 2 bits etc...

Страница 49: ...ently only four demodulator types are supported Digital Phase demodulator PSK for phase modulated signals Digital FM demodulator FSK for frequency modulated signals Digital AM demodulator ASK for ampl...

Страница 50: ...urposes only it is important to know what kind of processing is being applied to the analyzed channel PSK inspector AGC VGA fs k PLL Costas SRRC N CR Gardner CMA 2 5 dB To subcarrier channelizer The P...

Страница 51: ...frequency modulated signals and while shares most of the blocks of the PSK inspector there are important differences The PLL is replaced by a quadature demodulator which implements the formula xnx n...

Страница 52: ...hey de ne a view over the channel handled by an inspector SigDigger supports different types of inspection tabs thanks to its extensible plugin interface e g the APT Inspector provided by the APT deco...

Страница 53: ...k sockets in different formats Useful if you want SigDigger to be part of a longer DSP chain split in different applications Independently of the modulation this control group should let the user impl...

Страница 54: ...data rate is high The Reset button resets the maximum number of plot updaters per second to 60 fps If the CPU burn button is checked all the plot update limits are ignored and updates are triggered a...

Страница 55: ...ampling window Displays the decided symbols in shades of gray Highly dependent on the selected decision intervals Waveform displays the waveform of the demodulated samples similar to the waveform view...

Страница 56: ...cyclostationary analysis stream computed from the product of each sample by the conjugate of the previous Used to gather information on symbol tim ing Signal exponentiation N Spectrum of the N th powe...

Страница 57: ...with the Power spectrum source enabled to see the effects of these adjust ments For the particular case of PSK signals the Signal exponentiation spectrum source has the effect of exaggerating the fre...

Страница 58: ...imators for the same parameter In the early days of suscan when the PSK inspector was the only available inspector the rst baud rate estimator to be implemented was based in fast auto correlations FAC...

Страница 59: ...s DSP chain These blocks are used to switch from automatic or user de ned gain control If Auto is set the gain of the channelized signal is stabilized according to the current symbol period with a me...

Страница 60: ...performed in the feedback loop FSK demodulator The FSK demodulator is a rather simple block that is constantly computing estimations of the derivative of the phase using a clever trick based on the pr...

Страница 61: ...s Algorithm equalizer is implemented This equalizer exploits the fact that in the absence of multipath propagation symbols are evenly distributed along a circumference in the I Q plane This lack of ci...

Страница 62: ...t is going to be delivered Variable and how is it going to be represented Type The rationale is that although the underlying data is always the same a stream of demodulated complex IQ samples xn the u...

Страница 63: ...saved les is channel capture Modulation Rate baud NNNN wav With Modulation being the inspector s modulation AM FM or PM Rate the nominal symbol rate of the sample stream as speci ed in Clock recovery...

Страница 64: ......

Страница 65: ...noramic spectrum before hopping to the next frequency Interface overview The panoramic spectrum window can be accessed either from the View menu or by pressing Ctrl P P Although the interface has been...

Страница 66: ...he edges of the antialias lter right after fc fs 2 and right before fc fs 2 Device gains the current device gain con g if the device supports it Clicking Start scan commences the sweep The Reset butto...

Страница 67: ...removed With this con guration these artifacts will always show up in the same location making easier to tell them apart from actual signals Saving data The resulting spectrum may be saved as a Matlab...

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