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--- mission:log:2014:08:08:darc-side-of-munich-hunting-fm-broadcasts-for-bus-and-tram-display-information-on-90-mhz [2014/08/31 09:27] – [DARC signal candidate] chrono
+++ mission:log:2014:08:08:darc-side-of-munich-hunting-fm-broadcasts-for-bus-and-tram-display-information-on-90-mhz [2016/04/13 06:36] (current) – [Broadcast FM Primer] chrono
@@ Line 49: / Line 49: @@
 //The new infrastructure, tested by the MVG since 2011 and deployed since 2013, seems to be the [[http://www.axentia.se/pt/ibus_display.html|Axentia iBus FM/DARC]] public transport information system. The units are battery powered (with a supposed 3 year cycle) and receive near real-time updates via [[wp>Data_Radio_Channel|Data Radio Channel (DARC)]], embedded into the signal of FM broadcast news radio station B5 Aktuell, transmitted from Ismaning. DARC is a digital 16 kbps LMSK component, centered on 76 kHz (4th harmonic of the 19 kHz stereo pilot tone), of the WBFM (Wide-Band Frequency Modulation) composite signal found on 90.0 MHz.//
+Thanks to codec, we have a revealing bootloop video:
+{{:mission:log:2014:08:08:axentia-ibd-darc-display-mvg-boot-loop.mp4|}}
+{{:mission:log:2014:08:08:axentia-ibus-ibd-3720-mvg-muenchen-boot.jpg?315| }}
+{{ :mission:log:2014:08:08:axentia-ibus-ibd-3720-mvg-muenchen-fw.jpg?315|}}
 ==== Broadcast FM Primer ====
@@ Line 61: / Line 65: @@
 [{{:mission:log:2014:08:08:fm-broadcast-band-2mhz-90m-center-fftp-spectrum-waterfall.jpg?242|2Msps 90MHz osmocom_fft -F}}]
 [{{:mission:log:2014:08:08:fm-broadcast-band-960k-90m-center-fftp-spectrum-waterfall.jpg?345|960ksps 90MHz DARC-Hunter.grc}}]
@@ Line 67: / Line 72: @@
 **This looks fancy, but I don't know how to interpret it...**
-The spectrum chart shows what's going on right now, the waterfall gives you the same information, but as a sequence of spectrum chart slices stacked together over a period of time and observed from the top, which is an invaluable tool to actually watch and observe frequency ranges and modulations.
+The spectrum chart (left top/right bottom) shows what's going on right now, the waterfall (left bottom/right top) gives you the same information, but is a sequence of spectrum charts stacked together and observed from the top as 3 dimensional chart, showing time (y), frequency (x) and signal strength (z), which is an invaluable tool to actually watch and observe frequency ranges and modulations over a period of time, to recognize patterns visually.
 It's also interesting to note, how the spectrum of B5 on 90.0 MHz is clearly distinguishable from the other broadcasting stations in the RF baseband. There seem to be two signals 76 kHz left and right from 90.0 MHz
@@ Line 89: / Line 94: @@
 **Stereo Difference Signal**
-The stereo difference signal (L−R) is modulated onto a 38 kHz double-sideband suppressed-carrier (DSB-SC) signal occupying the baseband range of 23 to 53 kHz. A 19 kHz pilot tone, at exactly half the 38 kHz sub-carrier frequency and with a precise phase relationship to it, is also generated. This is transmitted at 8–10% of overall modulation level and used by the receiver to regenerate the 38 kHz sub-carrier with the correct phase.
+The stereo difference signal (L−R) is modulated onto a 38 kHz double-sideband suppressed-carrier (DSB-SC) signal occupying the baseband range of 23 to 53 kHz.
 **RDS**
@@ Line 95: / Line 100: @@
 The RDS sub-carrier transmits digital data at 1187.5 bps on a sub-carrier centered on 57 kHz, which is the 3rd harmonic of the 19 kHz FM stereo pilot tone, to minimize interference and intermodulation between the data signal, the stereo pilot and the 38 kHz DSB-SC stereo difference signal. The stereo difference signal extends up to 38 kHz + 15 kHz = 53 kHz, leaving 4 kHz for the lower sideband of the RDS signal.
-**DARC**\\
+**DARC**
 <WRAP round info>
 **DARC Primer**:\\
-http://www.axentia.se/db/DARC%20Technology.pdf
+http://www.axentia.se/db/DARC%20Technology.pdf\\
+\\
+**DARC Protocoll Specification:**\\
+[[http://www.etsi.org/deliver/etsi_en/300700_300799/300751/01.02.01_60/en_300751v010201p.pdf| ETSI EN 300 751 V1.2.1]]
 </WRAP>
@@ Line 110: / Line 118: @@
 ==== Test-Setup ====
-  * RTL SDR Sticks: Hama-Nano (E4K) / Scalar (RM820)
+In case you want to to re-verify the results or look through the bands where ever else you might live, here's a little documentation about the setup to have somewhat comparable results.
-  * Antenna: 3m dipole for 90.0 MHz (horizontal polarization)
-  * Software: gqrx, osmocom_fft, rtl_fm, gnuradio-companion
+=== Hardware ===
+**RTL SDR Sticks**
+  * Hama-Nano (E4K) as already described [[mission:log:2012:05:06:rtlsdr-osmosdr-gnuradio-fm-receiver|here]]
+  * [[http://www.amazon.de/gp/product/B00FVGOMIO/|Scalar (R820T) (13 EUR)]]
+**Antenna**
+A DIY 3m dipole designed for 90.0 MHz (horizontal polarization) hacked out of 75 ohms TV coax and two 83cm legs of silver speaker wire, one connected to coax center and the other to the shield. The speaker cables are taped to a beam (wood), the coax leaves in the center, giving a T shaped configuration. Another set of extremely [[http://www.amazon.de/dp/B002E4UZVY|cheap industry produced FM antennas]] have been tested and work equally well, if you don't want to hack your own.
+=== Software ===
+All software used here is free and open-source, of course:
+  * [[http://gnuradio.org/|GNU Radio 3.7.4]]
+  * [[http://sdr.osmocom.org/trac/wiki/GrOsmoSDR|gr-osmosdr - Provides GR sink and useful console utils (osmocom_fft etc.)]]
+  * [[http://sdr.osmocom.org/trac/wiki/fosphor|gr-fosphor - Awesome OpenCL/GL FFT Spectrum/Waterfall]]
+  * [[http://sdr.osmocom.org/trac/wiki/rtl-sdr|rtl-sdr - Provides GR sink and useful console utils (rtl_fm etc.)]]
+  * [[http://sdr.osmocom.org/trac/wiki/sdrangelove|SDRangelove - QT5/GR based all-in-one-receiver]]
+  * [[http://gqrx.dk/|gqrx - Another QT/GR based all-in-one receiver]]
+<WRAP round tip>
+When GNU Radio produces **choppy audio** with pulseaudio and logs a lot of **aUaUaUaU**'s in the console, you can try the following fix, it helped here:
+</WRAP>
+<code>$ vi ~/.gnuradio/config.conf</code>
+<sxh text; toolbar:false>
+[audio_alsa]
+nperiods = 16
+period_time = 0.100
+</sxh>
+**Flowgraph of a quick hack in GRC to verify the DARC channel**
 {{:mission:log:2014:08:08:gnuradio-darc-hunter-mk5-flowgraph.jpg|gnuradio-darc-hunter-mk5-flowgraph}}
@@ Line 118: / Line 159: @@
 <WRAP round download>
 **Download DARC-Hunter.grc File:**\\
-coming after cleanup
+[[https://apollo.open-resource.org/downloads/darc-hunter-mk5.grc|darc-hunter-mk5.grc]]
 </WRAP>
 ==== Negative reference stereo FM station ====
@@ Line 153: / Line 194: @@
 |  **76**  |  4th  | DARC Center | Digital Signal | DARC signal candidate|
-The big surprise here is that B5 seems to be a mono signal, all stereo components are missing in the multiplex mix. However, on the 4th we can clearly see a digital signal that matches the characteristics we would expect from a DARC signal. Let's see how it looks when we get even closer:
+The big surprise here is that B5 seems to be a mono signal, all stereo components are missing in the multiplex mix. However, on the 4th we can clearly see a digital signal that matches the characteristics we would expect from a DARC signal. LMSK modulation would need a pilot tone for synchronization but as this is a mono signal there is no pilot tone. According to ETSI EN 300 751 DARC will just simply be MSK modulated. Let's see how it looks when we get even closer:
 {{:mission:log:2014:08:08:fm-broadcast-band-96k-90m-center-demultiplexed-darc-fftp-spectrum-waterfall.jpg}}
@@ Line 253: / Line 294: @@
 **L/MSK Links:**
+[[https://github.com/zacinaction/kicksat/wiki/Radio-Info]]
 [[http://patentimages.storage.googleapis.com/EP1843535A1/imgf0001.png]]
 [[http://www.dsplog.com/2009/06/16/msk-transmitter-receiver/]]
@@ Line 258: / Line 300: @@
 [[http://signals-analysis.blogspot.com/2009/06/fsk-gfsk-msk-gmsk-and-some-other-modes.html|http://signals-analysis.blogspot.com/2009/06/fsk-gfsk-msk-gmsk]]
+[[http://www.ne.jp/asahi/hamradio/je9pel/aausati2.htm]]
+===== Updates =====
+  * [[https://github.com/muccc/darc|DARC GNU Radio Block Implementation]] by chris007 & andz - presented at [[https://eh15.easterhegg.eu/frab/en/eh15/public/events/2|EH2015]]
+  * [[mission:log:2016:04:12:the-darc-knight-rises]]
-{{tag>darc rf sdr gnuradio bus tram software hacking munich mvg research}}
+{{tag>darc rf sdr rtl-sdr hackrf gnuradio grc bus tram software hacking munich mvg research radio antenna}}
-{{keywords>Apollo-NG apollo next generation hackerspace hacker space development makerspace fablab diy community open-resource open resource mobile hackbus darc mvg rf sdr gnuradio bus tram software hacking munich mvv 76kHz research}}
+{{keywords>Apollo-NG apollo next generation hackerspace hacker space development makerspace fablab diy community open-resource open resource mobile hackbus darc mvg rf sdr gnuradio grc bus tram software hacking munich mvv 76kHz research radio }}
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