SignalScopePage » History » Version 8
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 | * Frank's gr-fsk4 block |
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| 9 | * The op25 repeater block |
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| 10 | |||
| 11 | 6 | max | The Python Numeric package is now also required. If you're running Debian or Ubuntu: |
| 12 | {{{ |
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| 13 | apt-get install python-numeric |
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| 14 | }}} |
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| 15 | 1 | max | |
| 16 | 6 | max | Other than these pre-reqs, no special setup or installation is needed. |
| 17 | |||
| 18 | 5 | max | There are three overall options or modes depending on your hardware; these are |
| 19 | * USRP |
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| 20 | * External receiver with discriminator tap connected to sound card |
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| 21 | * External receiver with IF in the audio sound card range (e.g., 24 KHz), referred to as "audio IF" |
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| 22 | 3 | max | |
| 23 | 1 | max | == Running with the disc-tap option == |
| 24 | |||
| 25 | The signal scope does not require the USRP. If you have a discriminator-tapped receiver, use the "-a" option: |
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| 26 | 3 | max | {{{ |
| 27 | 5 | max | ./scope.py -a -v 25 -g 50 |
| 28 | 3 | max | }}} |
| 29 | |||
| 30 | == Running with the USRP == |
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| 31 | |||
| 32 | It's helpful to find out the current calibration error beforehand (I use kalibrate), for example, +1234 hertz: |
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| 33 | {{{ |
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| 34 | 1 | max | ./scope.py -f 412.34e6 -RA -g 65 -c 1234 -v 25 |
| 35 | 3 | max | }}} |
| 36 | 1 | max | |
| 37 | 5 | max | == Running in the Audio IF mode == |
| 38 | 1 | max | |
| 39 | 5 | max | Receivers equipped with an IF output in the sound card range can be used. This is known as "audio IF" mode. |
| 40 | 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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| 41 | |||
| 42 | {{{ |
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| 43 | ./scope.py -A -c 24e3 -g 50 -v 25 |
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| 44 | }}} |
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| 45 | |||
| 46 | 4 | max | == Feature overview == |
| 47 | |||
| 48 | * Spectrum plot |
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| 49 | * Baseband oscilloscope |
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| 50 | 1 | max | * Eye Pattern Diagram (Datascope) display supporting several standard symbol rates |
| 51 | 4 | max | * Constellation Diagrams |
| 52 | * Demodulated Symbol Output |
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| 53 | 6 | max | * Correlation (including Fast Auto-Correlation) |
| 54 | 1 | max | * Direct-frequency entry, signal gain and fine-tuning controls |
| 55 | * User-selectable demodulator (FSK4 or QPSK) |
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| 56 | 5 | max | |
| 57 | In the USRP and audio-IF modes, several additional program functions are enabled (spectrum FFT, constellation diagram, PSK demod, and iDEN correlation). |
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| 58 | |||
| 59 | In all modes, the {{{--wireshark}}} option is used to write received P25 packet data to Wireshark. |
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| 60 | 4 | max | |
| 61 | == Spectrum Display == |
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| 62 | |||
| 63 | [[Image(a.png)]] |
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| 64 | |||
| 65 | The controls arranged along the bottom of the page are: |
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| 66 | * Frequency: to retune, type the new frequency here and press ENTER |
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| 67 | * Signal Gain: adjusts the baseband (demodulated) signal level |
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| 68 | * Fine Tune: adjusts tuning frequency over +/- 3000 Hz range |
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| 69 | * Demod: Selects demodulator (currently used in Demodulated Symbols only) |
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| 70 | Except for the signal gain control, these controls are only available in USRP RX mode. |
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| 71 | |||
| 72 | == Eye Pattern Diagrams == |
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| 73 | |||
| 74 | The scope input source can be connected either before or after the symbol filter using the Viewpoint toggle. |
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| 75 | |||
| 76 | Also the proper speed must be selected from the available options. |
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| 77 | |||
| 78 | [[Image(b.png)]] |
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| 79 | |||
| 80 | == Constellation Diagram == |
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| 81 | |||
| 82 | 7 | max | [[Image(f.png)]] |
| 83 | |||
| 84 | The signal scope also features an angular population graph (shown above) in addition to the traditional constellation display. |
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| 85 | 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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| 86 | 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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| 87 | result, and that the results are arranged in polar form instead of rectangular form. |
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| 88 | |||
| 89 | 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 |
| 90 | between the symbol decision points. The plots below illustrate the difference, with poorer convergence showing on the left image: |
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| 91 | 1 | max | |
| 92 | 8 | max | [[Image(mhp7a.png)]][[Image(c.png)]] |
| 93 | |||
| 94 | 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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| 95 | successive symbols are chosen from two distinct constellations (each containing four possible symbol values) separated by 45° |
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| 96 | |||
| 97 | 4 | max | == Demodulated Symbols == |
| 98 | |||
| 99 | [[Image(d.png)]] |
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| 100 | |||
| 101 | 1 | max | == Correlation == |
| 102 | |||
| 103 | [[Image(e.png)]] |
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| 104 | 8 | max | |
| 105 | Also included is Frank's Fast Auto Correlation (fac): |
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| 106 | |||
| 107 | [[Image(g.png)]] |
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| 108 | |||
| 109 | == BUGS == |
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| 110 | |||
| 111 | Possibly bugs exist, here are a few of the known ones as of this writing |
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| 112 | * Symbol filters totally brain damaged (need separate filters for each speed) |
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| 113 | * When switching modes using the notebook tabs, leftover data from before may appear momentarily |
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| 114 | * Highest and lowest speeds are not well tuned resulting either in sluggish updates or CPU exhaustion |
