tag:blogger.com,1999:blog-5096278891763426276.post3892872685202649080..comments2024-03-28T18:37:12.987+02:00Comments on absorptions: How I discovered RDSOona Räisänenhttp://www.blogger.com/profile/08764440174916554983noreply@blogger.comBlogger15125tag:blogger.com,1999:blog-5096278891763426276.post-15015631735059574332015-05-09T21:41:29.507+03:002015-05-09T21:41:29.507+03:00RDS is quite a topic in its self with so much info...RDS is quite a topic in its self with so much information being sent in approximately 1200 baud. A reason why RDS is leaking into the audio has to do with its proximity to the upper sideband of the difference signal. FM stereo difference is a form of AM called DSBSC or double sideband suppressed carrier. The two sidebands are mirror images of each other with the upper sideband being accurate to the original audio. The highest audio frequency determines the highest modulating frequency which is actually 53 KHz resulting in a very narrow guard band between it and the RDS sub carrier which centers at 57 KHz. An earlier comment about the artifact being a mixing image is pretty accurate. 57 is a multiple of 19 which in this case means 19 KHz for the FM stereo pilot and by the way 38 is also a multiple of it too.Anonymoushttps://www.blogger.com/profile/05649477321111738640noreply@blogger.comtag:blogger.com,1999:blog-5096278891763426276.post-4682959831586405262015-04-09T14:39:32.206+03:002015-04-09T14:39:32.206+03:00http://i.imgur.com/MeqjM9i.jpg
I reproduced this u...http://i.imgur.com/MeqjM9i.jpg<br />I reproduced this using MPX tool and software MPX signal generator. I noticed this phenomenon some time ago. It turned out to be the "MPX" bug - always present :) Though, some high end tuners with proper LPF filters don't let the RDS and pilot tone leak into the audio.Anonymoushttps://www.blogger.com/profile/14464780542824374813noreply@blogger.comtag:blogger.com,1999:blog-5096278891763426276.post-86169794126274719472014-02-04T14:24:38.977+02:002014-02-04T14:24:38.977+02:00It's on every channel. It comes from the stere...It's on every channel. It comes from the stereo decoder circuit.Oona Räisänenhttps://www.blogger.com/profile/08764440174916554983noreply@blogger.comtag:blogger.com,1999:blog-5096278891763426276.post-41327376036944345062014-02-04T13:41:31.027+02:002014-02-04T13:41:31.027+02:00Looks like the RDS encoder output has become dirty...Looks like the RDS encoder output has become dirty, or possibly the pilot tone level is set too high and is over deviating. It would explain why the 19 KHz bandwidth is wider than normal.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-5096278891763426276.post-88472738679311275332014-02-02T02:25:23.421+02:002014-02-02T02:25:23.421+02:00why are girls the best hackers? you fucking rock!...why are girls the best hackers? you fucking rock!! keep it up!Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-5096278891763426276.post-74085943202197979112014-02-01T22:22:36.026+02:002014-02-01T22:22:36.026+02:00I have an FM radio that I modified by removing all...I have an FM radio that I modified by removing all but one capacitor from the demodulator/low-pass filter. The cap I kept, filters out the 10.7 Mhz IF, but allows everything else to pass through. I built a Ramsey Kit PLL based SCA decoder kit, which I modified by adding better high-pass filtering. It easily tunes into the analog SCA signals on 67 and 92 Khz, but it can also detect data at 57 Khz, converting it unto audible frequencies. I haven't bothered to try to decode any of them, as I am more of an analog geek than a CPU coding geek. :) I'm positive that you're right about the stereo decoder of your radio creating that "image" of the RDS near the 19Khz pilot. Nice work! :)Willie...http://www.mymorninglight.org/hamnoreply@blogger.comtag:blogger.com,1999:blog-5096278891763426276.post-20624051137303457582014-01-15T20:35:08.954+02:002014-01-15T20:35:08.954+02:00It's not about the sound card, I've tested...It's not about the sound card, I've tested that. It's the radio's stereo demux circuitry. It goes away if I switch off stereo demuxing.Oona Räisänenhttps://www.blogger.com/profile/08764440174916554983noreply@blogger.comtag:blogger.com,1999:blog-5096278891763426276.post-51929812399761596582014-01-15T18:50:02.077+02:002014-01-15T18:50:02.077+02:00It might be because you are sampling with your sou...It might be because you are sampling with your soundcard, you are sampling at 44 khz approx? and that is too slow to see the spectrum at 57 khz, but because of an sampling effect, it does appear anyway, and since the data rate is slower than your sampling speed, it's perfectly fine to demod. it would be fun to know if you could sample faster and see if my theory is right, and it is interesting that the signal disappears when you go mono, it could be your explanation too.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-5096278891763426276.post-75104025987880001022013-12-13T12:25:46.300+02:002013-12-13T12:25:46.300+02:00Great blog! Loved the articles on DARC, RDS and th...Great blog! Loved the articles on DARC, RDS and the Atomic Powered Robot...<br />I have been playing with RDS lately, and posted some results here:<br />http://migblog.blog.com/2013/12/12/waterfall-display-for-fm-broadcast/<br />Regards, mig.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-5096278891763426276.post-7847900990503526512013-06-05T02:17:06.266+03:002013-06-05T02:17:06.266+03:00Great blog and excellently documented projects! We...Great blog and excellently documented projects! Well done!<br /><br />Your signal "geekiness" reminds me of a long-forgotten fun-project plan I had. Using a digital storage oscilloscope and a highly sensitive receiver with flat and wide selectivity in the 1-100 KHz range and an appropriate antenna, one can eavesdrop the electromagnetic waves emitted from keystrokes of any PS/2 (and not only) based keyboard. After sampling the signal, (the fun part) is to write a signal processing script that would decrypt the collected keystroke data. Sounds evil and must be used only for learning purposes of course :)<br /><br />Here are some enthusiasts that have in fact done it: http://www.youtube.com/watch?v=AFWgIAgMtiA <br /><br />So that's just a thought I've had long ago in my mind. Hope you don't get me wrong, it's only the technical side of that task that's intriguing. :)Deyan Levskihttp://www.dilemaltd.com/deyan-levski/en/index.htmnoreply@blogger.comtag:blogger.com,1999:blog-5096278891763426276.post-87229412725562762312013-05-06T11:01:40.270+03:002013-05-06T11:01:40.270+03:00For a little more bandwidth I wrote a little pytho...For a little more bandwidth I wrote a little python ditty that grabs data from a scope and dumps it to baudline via stdin:<br /><br />http://www.urlme.net/blog/?p=2031Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-5096278891763426276.post-68350034616503248022013-04-24T10:05:05.731+03:002013-04-24T10:05:05.731+03:00It's not actually that close to the audio pass...It's not actually that close to the audio passband, it's just an artifact produced by my radio. The RDS subcarrier is at 57 kHz.Oona Räisänenhttps://www.blogger.com/profile/08764440174916554983noreply@blogger.comtag:blogger.com,1999:blog-5096278891763426276.post-7812788768140330442013-04-24T05:07:00.630+03:002013-04-24T05:07:00.630+03:00RDS is relatively-ish well-known. I know that SDR#...RDS is relatively-ish well-known. I know that SDR# decodes it in WFM mode. I didn't know it was so close as to actually interfere with the highest part of the audio passband, though!<br /><br />The real ticket is decoding the digital broadcasts over here in the States where it's "HD Radio" and everything is patent encumbered and terrible. I think there are DAB/DAB+ decoders already written for the rest of the world's standard, though.masonhttps://www.blogger.com/profile/02433162298265228584noreply@blogger.comtag:blogger.com,1999:blog-5096278891763426276.post-6094519972918427192013-04-22T15:25:01.257+03:002013-04-22T15:25:01.257+03:00I hope that's a good thing.I hope that's a good thing.Oona Räisänenhttps://www.blogger.com/profile/08764440174916554983noreply@blogger.comtag:blogger.com,1999:blog-5096278891763426276.post-66254114292875978562013-04-22T11:44:56.540+03:002013-04-22T11:44:56.540+03:00This is so cool, I can't even explain!This is so cool, I can't even explain!Anonymoushttps://www.blogger.com/profile/08627420814251615186noreply@blogger.com