SignalScopePage » History » Version 14
max, 04/22/2017 04:04 PM
1 | 1 | max | = Signal Scope = |
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2 | |||
3 | == Installation == |
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4 | |||
5 | 6 | max | Before running the scope app, check that the following standard pre-requisite packages are also installed: |
6 | 1 | max | * GNU Radio |
7 | * The op25 blocks |
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8 | * The op25 repeater block |
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9 | |||
10 | 14 | max | The osmosdr http://sdr.osmocom.org/trac/wiki/GrOsmoSDR package is required when using USRP or HackRF (or other hardware supported by osmosdr) |
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12 | Additionally, hamlib http://sourceforge.net/apps/mediawiki/hamlib/index.php?title=Main_Page is (optionally) needed if using a frequency-agile receiver that is to be tuned using hamlib (see below) |
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13 | |||
14 | The Python Numeric package is also needed when using autocorrelation. If you're running Debian or Ubuntu: |
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15 | 6 | max | {{{ |
16 | apt-get install python-numeric |
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17 | 1 | max | }}} |
18 | 6 | max | |
19 | 1 | max | Other than these pre-reqs, no special setup or installation is needed. |
20 | 11 | max | |
21 | 1 | max | == Targets == |
22 | 14 | max | * Choice of osmosdr(uhd / hackrf, etc), discriminator-tap, or "audio-IF" hardware modes |
23 | 1 | max | * Supports either GL or non-GL display mode |
24 | * Both FSK4 and CQPSK demodulation modes supported |
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25 | 14 | max | * Lower and middle range PC hardware, not just the latest (optional features require more CPU) |
26 | 11 | max | |
27 | == Running the Program == |
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28 | |||
29 | 14 | max | There are four overall options or modes depending on your hardware; these are |
30 | * Osmosdr |
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31 | * Hamlib |
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32 | 1 | max | * External receiver with discriminator tap connected to sound card |
33 | 11 | max | * External receiver with IF in the audio sound card range (e.g., 24 KHz), referred to as "audio IF" |
34 | 3 | max | |
35 | 1 | max | === Running with the disc-tap option === |
36 | |||
37 | 9 | max | The signal scope does not require the USRP. If you have a discriminator-tapped receiver, use the "-a" option: |
38 | 3 | max | {{{ |
39 | 1 | max | ./scope.py -a -v 10 -g 50 |
40 | }}} |
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41 | |||
42 | 14 | max | === UHD example === |
43 | 1 | max | |
44 | {{{ |
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45 | 14 | max | ./scope.py --args 'uhd,nchan=1,subdev=B:0' -g 65 -f 412.34e6 -o 50e3 -V -v 0 -T 412.34e6 -N 'ADC-pga:10,PGA0:29' -c 7500 |
46 | 1 | max | }}} |
47 | |||
48 | 14 | max | === HackRF example === |
49 | {{{ |
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50 | ./scope.py --args 'hackrf' -g 65 -f 412.34e6 -N 'RF:14,IF:32,BB:26' -o 50e3 -c 2500 -T 412.34e6 -V -v 0 |
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51 | }}} |
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52 | |||
53 | === Hamlib example === |
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54 | Two receivers in cascade (USRP with LFRX connected to the 455 KHz IF output terminal of hamlib-controlled receiver) |
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55 | {{{ |
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56 | ./scope.py --args 'uhd,nchan=1,subdev=A:A' -g 65 -f 455e3 -o 50e3 -V -v 0 -H 1234 -T 412.34e6 |
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57 | }}} |
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58 | |||
59 | 11 | max | === Running in the Audio IF mode === |
60 | 1 | max | |
61 | 5 | max | Receivers equipped with an IF output in the sound card range can be used. This is known as "audio IF" mode. |
62 | A soundcard sampling rate of 96K is used and the IF frequency (typically 24 KHz) is given using the {{{--calibration}}} parameter: |
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63 | |||
64 | {{{ |
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65 | 9 | max | ./scope.py -A -c 24e3 -g 50 -v 10 |
66 | 5 | max | }}} |
67 | |||
68 | 4 | max | == Feature overview == |
69 | |||
70 | * Spectrum plot |
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71 | * Baseband oscilloscope |
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72 | 1 | max | * Eye Pattern Diagram (Datascope) display supporting several standard symbol rates |
73 | 4 | max | * Constellation Diagrams |
74 | * Demodulated Symbol Output |
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75 | 6 | max | * Correlation (including Fast Auto-Correlation) |
76 | 1 | max | * Direct-frequency entry, signal gain and fine-tuning controls |
77 | * User-selectable demodulator (FSK4 or QPSK) |
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78 | 5 | max | |
79 | 12 | max | In the baseband AF (disc. tap) mode, several program functions are disabled (spectrum FFT, constellation diagram, PSK demod, FAC and iDEN correlation) |
80 | because these functions require direct access to the signal with no demodulation. |
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81 | 5 | max | |
82 | In all modes, the {{{--wireshark}}} option is used to write received P25 packet data to Wireshark. |
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83 | 1 | max | |
84 | == Program Options == |
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85 | 10 | max | |
86 | Here is a full list of program options: |
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87 | {{{ |
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88 | Usage: scope.py [options] |
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89 | |||
90 | Options: |
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91 | -h, --help show this help message and exit |
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92 | 14 | max | --args=ARGS device args |
93 | --antenna=ANTENNA select antenna |
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94 | 10 | max | -a, --audio use direct audio input |
95 | -A, --audio-if soundcard IF mode (use --calibration to set IF freq) |
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96 | -I AUDIO_INPUT, --audio-input=AUDIO_INPUT |
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97 | 1 | max | pcm input device name. E.g., hw:0,0 or /dev/dsp |
98 | -i INPUT, --input=INPUT |
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99 | input file name |
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100 | -b Hz, --excess-bw=Hz |
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101 | for RRC filter |
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102 | -c Hz, --calibration=Hz |
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103 | USRP offset or audio IF frequency |
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104 | -C Hz, --costas-alpha=Hz |
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105 | value of alpha for Costas loop |
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106 | -f Hz, --frequency=Hz |
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107 | 10 | max | USRP center frequency |
108 | 14 | max | -F IFILE, --ifile=IFILE |
109 | read input from complex capture file |
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110 | -H HAMLIB_MODEL, --hamlib-model=HAMLIB_MODEL |
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111 | specify model for hamlib |
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112 | -s SEEK, --seek=SEEK ifile seek in K |
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113 | -S SAMPLE_RATE, --sample-rate=SAMPLE_RATE |
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114 | source samp rate |
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115 | -t, --tone-detect use experimental tone detect algorithm |
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116 | -T Hz, --trunk-cc-freq=Hz |
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117 | trunk control channel frequency |
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118 | 10 | max | -v VERBOSITY, --verbosity=VERBOSITY |
119 | message debug level |
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120 | 14 | max | -V, --vocoder voice codec |
121 | -o Hz, --offset=Hz tuning offset frequency [to circumvent DC offset] |
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122 | 10 | max | -p, --pause block on startup |
123 | 1 | max | -w, --wireshark output data to Wireshark |
124 | -W WIRESHARK_HOST, --wireshark-host=WIRESHARK_HOST |
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125 | Wireshark host |
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126 | 14 | max | -r RAW_SYMBOLS, --raw-symbols=RAW_SYMBOLS |
127 | dump decoded symbols to file |
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128 | 10 | max | -R RX_SUBDEV_SPEC, --rx-subdev-spec=RX_SUBDEV_SPEC |
129 | select USRP Rx side A or B (default=A) |
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130 | -g GAIN, --gain=GAIN set USRP gain in dB (default is midpoint) or set audio |
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131 | gain |
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132 | -G GAIN_MU, --gain-mu=GAIN_MU |
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133 | gardner gain |
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134 | 14 | max | -N GAINS, --gains=GAINS |
135 | gain settings |
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136 | -O AUDIO_OUTPUT, --audio-output=AUDIO_OUTPUT |
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137 | audio output device name |
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138 | 10 | max | }}} |
139 | |||
140 | 4 | max | == Spectrum Display == |
141 | |||
142 | [[Image(a.png)]] |
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143 | |||
144 | The controls arranged along the bottom of the page are: |
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145 | * Frequency: to retune, type the new frequency here and press ENTER |
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146 | * Signal Gain: adjusts the baseband (demodulated) signal level |
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147 | * Fine Tune: adjusts tuning frequency over +/- 3000 Hz range |
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148 | * Demod: Selects demodulator (currently used in Demodulated Symbols only) |
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149 | Except for the signal gain control, these controls are only available in USRP RX mode. |
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150 | |||
151 | == Eye Pattern Diagrams == |
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152 | |||
153 | The scope input source can be connected either before or after the symbol filter using the Viewpoint toggle. |
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154 | |||
155 | Also the proper speed must be selected from the available options. |
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156 | |||
157 | [[Image(b.png)]] |
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158 | |||
159 | == Constellation Diagram == |
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160 | |||
161 | 7 | max | [[Image(f.png)]] |
162 | |||
163 | The signal scope also features an angular population graph (shown above) in addition to the traditional constellation display. |
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164 | In this mode the symbol magnitude (distance from center) is discarded. Instead the circle is sliced into segments and a count |
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165 | of symbols found in each segment is plotted. This is similar to a histogram except that a straight line is drawn between each |
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166 | result, and that the results are arranged in polar form instead of rectangular form. |
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167 | |||
168 | 8 | max | With this display, the zone at the exact center of the plot can be used precisely to measure the degree of separation or margin |
169 | 13 | max | between the demodulated symbols. The plots below illustrate the difference, with poor separation showing on the left image as |
170 | revealed by the failure to converge at the center and by the clear territorial violations: |
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171 | 1 | max | |
172 | 8 | max | [[Image(mhp7a.png)]][[Image(c.png)]] |
173 | |||
174 | The two-color mode is used in these images, providing natural relief to highlight the distinctive feature of π/4 DQPSK in which |
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175 | successive symbols are chosen from two distinct constellations (each containing four possible symbol values) separated by 45° |
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176 | |||
177 | 4 | max | == Demodulated Symbols == |
178 | |||
179 | [[Image(d.png)]] |
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180 | |||
181 | 1 | max | == Correlation == |
182 | |||
183 | [[Image(e.png)]] |
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184 | |||
185 | 9 | max | Cross correlation allows rapid identification of signals with known characteristics. Frame Sync (FS) signatures of several commonly |
186 | used radio systems are included. |
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187 | |||
188 | By convention correlation results are usually displayed using positive correlation peaks only. In this system |
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189 | however it is possible (and legal) for negative correlation products to be produced. This can occur for two wholly separate reasons: |
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190 | * If the hardware polarity is inverted |
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191 | * When the FS symbols are purposely inverted as an integral part of protocol processing (commonly used in certain protocols but not used in P25) |
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192 | |||
193 | The first case commonly happens when using the disc-tap method of hardware connection, because the actual polarity of the signal seems to vary |
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194 | randomly among different sound cards and receivers. In one actual case, two PC's of the same PC brand bought from the same store had opposite polarity. |
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195 | |||
196 | The P25 software framer automatically detects the proper polarity and issues a message if negative polarity data is received: |
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197 | {{{ |
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198 | Reversed FS polarity detected - autocorrecting |
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199 | }}} |
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200 | |||
201 | The automatic correction applies only to software framing and doesn't help with correlation. For correct results for both software framing and |
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202 | correlation, you should correct the polarity reversal problem at its source; this is done using negative values for the {{{--gain}}} parameter at |
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203 | program start time: |
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204 | |||
205 | {{{ |
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206 | ./scope.py -a -v 10 -g -50 |
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207 | }}} |
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208 | |||
209 | The second cause of negative correlation peaks is that some protocols (although not P25) make use of both normal- and inverted-polarity FS |
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210 | sequences as a standard part of their processing. Instead of clogging the GUI menu with several choices that are merely inverses of others, |
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211 | 1 | max | just for the sake of always having positive-peaked correlations, we allow the correlation graph to reflect the natural polarity of the data. |
212 | 9 | max | Thus both + and - peaks are shown, allowing quick diagnosis of incorrect hardware polarity (see above), and allowing identification of the |
213 | 12 | max | particular family and sub-protocol in use. |
214 | 9 | max | |
215 | == Auto Correlation == |
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216 | |||
217 | 1 | max | Also included is Frank's Fast Auto Correlation (fac): |
218 | |||
219 | 8 | max | [[Image(g.png)]] |
220 | 9 | max | |
221 | For further details about Fast Auto Correlation refer to Frank's page at http://sites.google.com/site/radiorausch/ |
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222 | 8 | max | |
223 | == BUGS == |
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224 | |||
225 | Possibly bugs exist, here are a few of the known ones as of this writing |
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226 | 1 | max | * Symbol filters totally brain damaged (need separate filters for each speed) |
227 | * When switching modes using the notebook tabs, leftover data from before may appear momentarily |
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228 | * Highest and lowest speeds are not well tuned resulting either in sluggish updates or CPU exhaustion |
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229 | 11 | max | |
230 | == CREDITS == |
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231 | |||
232 | I ripped off the "tabbed notebook" theme (and code) from Stevie; it already had the spectrum, baseband, and decoded symbol displays. I added the data scope, constellation scope, and cross correlation features. |
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233 | |||
234 | The Fast Auto Correlation (fac) code came from Radiorausch. |
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235 | |||
236 | Special thanks to Mossmann for leaving one commented-out "print" statement in c4fm-decode.py. Of course it was tempting to wonder "what would happen" if that statement were un-commented. The final result? The cross-correlation feature. |
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237 | |||
238 | Special thanks also to GPL(v3), for encouraging these mashups. |