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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 [2014/12/06 12:19] – chrono | mission:log:2014:08:08:darc-side-of-munich-hunting-fm-broadcasts-for-bus-and-tram-display-information-on-90-mhz [2015/05/05 18:09] – [Updates] chrono | ||
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| Have a look at the following two images, which show the RF baseband spectral views in different sample sizes and different tools, both centered on 90 MHz with other broadcasting stations on 89.5 MHz and 90.6 MHz in the 2Msps view. | Have a look at the following two images, which show the RF baseband spectral views in different sample sizes and different tools, both centered on 90 MHz with other broadcasting stations on 89.5 MHz and 90.6 MHz in the 2Msps view. | ||
| - | [{{: | + | [{{: |
| [{{: | [{{: | ||
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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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| | **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:// | ||
| + | |||
| + | {{tag> | ||
| - | {{keywords> | + | {{keywords> |
| ~~DISCUSSION~~ | ~~DISCUSSION~~ | ||