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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 [2014/08/25 06:03] – [Broadcast FM Primer] chrono | mission:log:2014:08:08:darc-side-of-munich-hunting-fm-broadcasts-for-bus-and-tram-display-information-on-90-mhz [2016/04/12 18:47] – [Updates] chrono | ||
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* the ID | * the ID | ||
* the name of the stop and the direction | * the name of the stop and the direction | ||
- | [[https:// | + | in the [[https:// |
</ | </ | ||
===== ===== | ===== ===== | ||
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//The new infrastructure, | //The new infrastructure, | ||
- | |||
+ | Thanks to codec, we have a revealing bootloop video: | ||
+ | {{: | ||
+ | |||
+ | {{: | ||
+ | {{ : | ||
==== Broadcast FM Primer ==== | ==== Broadcast FM Primer ==== | ||
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[{{: | [{{: | ||
+ | |||
[{{: | [{{: | ||
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**This looks fancy, but I don't know how to interpret it...** | **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, | + | The spectrum chart (left top/right bottom) |
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 | 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 | ||
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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. | 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> | <WRAP round info> | ||
**DARC Primer**:\\ | **DARC Primer**:\\ | ||
- | http:// | + | http:// |
+ | \\ | ||
+ | **DARC Protocoll Specification: | ||
+ | [[http:// | ||
</ | </ | ||
- | The final multiplex signal can contain a combination of the Main Channel (L+R), the pilot tone, the sub-channel (L−R), the RDS channel and the DARC channel. This composite signal modulates the FM transmitter. | + | The final multiplex signal can contain a combination of the Main (Mono) |
**Enough with the theory already, let's have a peek** | **Enough with the theory already, let's have a peek** | ||
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==== Test-Setup ==== | ==== Test-Setup ==== | ||
- | | + | 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: | ||
+ | * [[http:// | ||
+ | |||
+ | **Antenna** | ||
+ | |||
+ | A DIY 3m dipole | ||
+ | |||
+ | === Software === | ||
+ | |||
+ | All software used here is free and open-source, | ||
+ | |||
+ | * [[http:// | ||
+ | * [[http:// | ||
+ | * [[http:// | ||
+ | * [[http:// | ||
+ | * [[http:// | ||
+ | * [[http:// | ||
+ | |||
+ | <WRAP round tip> | ||
+ | When GNU Radio produces **choppy audio** with pulseaudio and logs a lot of **aUaUaUaU**' | ||
+ | </ | ||
+ | |||
+ | < | ||
+ | <sxh text; toolbar: | ||
+ | [audio_alsa] | ||
+ | nperiods = 16 | ||
+ | period_time = 0.100 | ||
+ | </ | ||
+ | |||
+ | **Flowgraph of a quick hack in GRC to verify the DARC channel** | ||
{{: | {{: | ||
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<WRAP round download> | <WRAP round download> | ||
**Download DARC-Hunter.grc File:**\\ | **Download DARC-Hunter.grc File:**\\ | ||
- | coming after cleanup | + | [[https:// |
</ | </ | ||
==== Negative reference stereo FM station ==== | ==== Negative reference stereo FM station ==== | ||
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{{: | {{: | ||
+ | |||
+ | {{: | ||
^ kHz ^ H ^ Expected ^ Observed ^ Conclusion ^ | ^ kHz ^ H ^ Expected ^ Observed ^ Conclusion ^ | ||
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| **76** | | **76** | ||
- | 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: |
{{: | {{: | ||
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=== Decoding === | === Decoding === | ||
- | Now that we can say that we know the signal | + | At this point, it's reasonable to say, that we could verify |
http:// | http:// | ||
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https:// | https:// | ||
- | A quick preliminary test with darcdec was very unstable and didn't yield any usable results but we're obviously on the right track, considering the decoded network name: | + | A quick preliminary test with darcdec was rather |
< | < | ||
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???? | ???? | ||
</ | </ | ||
- | |||
- | |||
- | |||
So we either have to hack around in darcdec and find out why it's not putting out anything or we build something like a gr-darcdec module which can be used as a functional block in gnuradio (preferable). | So we either have to hack around in darcdec and find out why it's not putting out anything or we build something like a gr-darcdec module which can be used as a functional block in gnuradio (preferable). | ||
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=== Downloads === | === Downloads === | ||
- | Since this particular signal can only be received in Munich, here are some dump files to download, for smart minds anywhere else, who may enjoy the challenge to go after it too: | + | Since this particular signal can only be received in Munich, here are some dump files to download, for smart, creative or bored minds anywhere else, who may enjoy the challenge to go after it too. If you need more or other tools/ |
^ Tool | osmocom_fft | | ^ Tool | osmocom_fft | | ||
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**L/MSK Links:** | **L/MSK Links:** | ||
+ | [[https:// | ||
[[http:// | [[http:// | ||
[[http:// | [[http:// | ||
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[[http:// | [[http:// | ||
+ | [[http:// | ||
+ | |||
+ | ===== Updates ===== | ||
+ | |||
+ | * [[https:// | ||
+ | * [[mission: | ||
- | {{tag> | + | {{tag> |
- | {{keywords> | + | {{keywords> |
~~DISCUSSION~~ | ~~DISCUSSION~~ |