Differences
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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 [2014-11-05 12:38] – 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 | ||
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| [{{: | [{{: | ||
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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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| **Stereo Difference Signal** | **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** | **RDS** | ||
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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:// | ||
| </ | </ | ||
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| **Antenna** | **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 cheap industry produced FM antennas have been ordered | + | 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 |
| === Software === | === Software === | ||
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| < | < | ||
| - | <sxh> | + | < |
| [audio_alsa] | [audio_alsa] | ||
| nperiods = 16 | nperiods = 16 | ||
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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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| | **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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| [[http:// | [[http:// | ||
| - | {{tag> | + | ===== Updates ===== |
| + | |||
| + | * [[https:// | ||
| + | * [[mission: | ||
| + | |||
| + | {{tag> | ||
| - | {{keywords> | + | {{keywords> |
| ~~DISCUSSION~~ | ~~DISCUSSION~~ | ||