tag:blogger.com,1999:blog-5096278891763426276.post7458738290505064625..comments2024-03-13T19:12:58.863+02:00Comments on absorptions: Mystery signal from a helicopterOona Räisänenhttp://www.blogger.com/profile/08764440174916554983noreply@blogger.comBlogger89125tag:blogger.com,1999:blog-5096278891763426276.post-16641081236368285442022-07-11T12:45:23.144+03:002022-07-11T12:45:23.144+03:00https://youtu.be/QuDTlMM-raE?t=38https://youtu.be/QuDTlMM-raE?t=38Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-5096278891763426276.post-17765888413512283952022-07-08T09:14:18.456+03:002022-07-08T09:14:18.456+03:00I just stumbled upon this Yle video from a helicop...I just stumbled upon this Yle video from a helicopter in Japan:<br />https://areena.yle.fi/1-63018632<br /><br />And there seems to be a very similar, yet different, digital audio stream.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-5096278891763426276.post-9511737844816527662018-10-27T03:41:53.320+03:002018-10-27T03:41:53.320+03:00What fun! Well I know exactly what this is (as on...What fun! Well I know exactly what this is (as one of the original creators). You have most of it but missed a few details.. It is BELL202 running 7 data bits, one stop, odd parity. that adds up to 10 bits per char counting the start. What does all the data mean? the L #NA 272 0003.0 is the "bearing and range" to the site receiving the signal (the TV station tower). Start at the Lat/Long and then plot the bearing and range from there. Most likely the bearing is in "magnetic", but some transmit this in "true". Now for the next riddle: Where is the altitude?? Its there but the only part in binary and is in a magic grey code... Anonymoushttps://www.blogger.com/profile/07352108660341012236noreply@blogger.comtag:blogger.com,1999:blog-5096278891763426276.post-29859193091655850202017-04-03T19:28:04.994+03:002017-04-03T19:28:04.994+03:00You da real MVP, bro!You da real MVP, bro!Clint Laskowskihttps://www.blogger.com/profile/03009568520344916282noreply@blogger.comtag:blogger.com,1999:blog-5096278891763426276.post-38730590821131954752017-02-05T19:52:42.446+02:002017-02-05T19:52:42.446+02:00Can you make the perl script available?...on githu...Can you make the perl script available?...on github?<br />better yet can you provide us with your(perl) Hex tool which you highlighted the octets...Image #3 on this page?Anonymoushttps://www.blogger.com/profile/06235182763264799354noreply@blogger.comtag:blogger.com,1999:blog-5096278891763426276.post-75998328649468339722015-09-23T02:35:59.045+03:002015-09-23T02:35:59.045+03:00I just had to log in to comment. I remember watchi...I just had to log in to comment. I remember watching Contact as a kid (I can admit I cried). Awesome touching movie but it never got me into HAM or signal analysis.jirikihttp://jiriki.kapsi.fi/noreply@blogger.comtag:blogger.com,1999:blog-5096278891763426276.post-40774396868509756372015-06-25T12:51:57.238+03:002015-06-25T12:51:57.238+03:00Thanks for the comment!
The telemetry is separate...Thanks for the comment!<br /><br />The telemetry is separated from the voice audio by simple stereo separation, and will not normally be broadcast on TV.<br /><br />You can decode 7-bit Bell202 using <a href="http://www.whence.com/minimodem/" rel="nofollow">minimodem</a>. You can read more about the Bell202 interface in <a href="http://www.softelectro.ru/bell202_en.html" rel="nofollow">this 1976 document</a>.Oona Räisänenhttps://www.blogger.com/profile/08764440174916554983noreply@blogger.comtag:blogger.com,1999:blog-5096278891763426276.post-43274431741726855282015-06-25T10:17:33.290+03:002015-06-25T10:17:33.290+03:00I've heard this signal to, and it's always...I've heard this signal to, and it's always coming from a helicopter news reporting. However it's usually NOT on during the entire duration of the helicopter reporter doing their news report. It usually comes on just after the person in the helicopter says "now back to [insert anchor-man's name here] in the newsroom" and switches off their broadcast signal from the helicopter (maybe accidentally switching on their telemetry too soon). I've never heard it on any news broadcast for more than 1 second. It's very interesting to see that you have a much longer sample of it here. How did you get it?<br /><br />It seems that they have no reason to send the telemetry over the same channel as voice audio, as that messes up the sound of the person you are trying to listen to. Why not have a separate transmitter and antenna dedicated to telemetry?<br /><br />Also, it's NOT 7bit ascii (or at least not being sent "in the clear"). 7bit ascii standard is 2 start bits (or sometimes 1 start bit), 7 data bits (for ham radio, though other applications usually use 8 data bits), 0 parity bits, and 1 stop bit. A start bit is a binary 0, and a stop bit is a binary 1. Also the bit order is usually MSB first.<br /><br />I have a ham radio decoder software capable of decoding raw 7bit ascii FSK stream at any baud rate, and any frequency shift, and it can't decode this thing. I tried both polarities (upper tone = binary 1, and lower tone = binary 1). Neither polarity decoded it. It can also decode 4 modes of ascii (including non-standard variants). Ascii 8 bits per byte, Ascii 7 bits per byte, Ascii 8 with MSB clear (7 bits, with one 0 bit for padding to 8 bits), and Ascii 8 with even parity (8 data bits plus a parity bit for a total of 9 bits between the startbits and stopbits). I tried all for of these modes with both tone polarities. It only decodes random garbage. I tend to believe that this signal is in fact encrypted, and you managed to somehow crack the encryption to decode it.Benhttps://www.blogger.com/profile/15541936450045427082noreply@blogger.comtag:blogger.com,1999:blog-5096278891763426276.post-48493720360717702352015-06-19T17:36:30.456+03:002015-06-19T17:36:30.456+03:00Hey Oona,
Awesome post! I have read through it a ...Hey Oona,<br /><br />Awesome post! I have read through it a few times now and each time I come away with something new to learn about. Thanks!<br /><br />Also, I found this video https://vimeo.com/111414803 of you explaining the process above. Didn't see it linked here so I posted it for the benefit of the other readers.<br /><br />Cheers!<br />-BrandonAnonymoushttps://www.blogger.com/profile/17180018977254729027noreply@blogger.comtag:blogger.com,1999:blog-5096278891763426276.post-20168740573615787732015-02-11T01:07:25.499+02:002015-02-11T01:07:25.499+02:00Hi Oona,
I'll add my compliments to the pile....Hi Oona,<br /><br />I'll add my compliments to the pile. It's incredible work. Also, I imagine the posters you've kicked out will start popping up in classrooms. Few electronics teachers "get" aesthetics and infographics the way you do.<br /><br />Here's another system in use by broadcasters for helicopter tracking...<br /><br />http://www.trollsystems.com/index.php/video-and-data-links-2/bidirectional-data-links<br /><br />Note, there's a "sample manual" with photos of the receive station user interface on page 3-26.<br /><br /><br />http://test.trollsystems.com/media/files/Directional%20Diversity%20Ground%20Receive%20System.pdf<br /><br />Another Alex<br />Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-5096278891763426276.post-5297284907894758532014-10-24T10:33:27.250+03:002014-10-24T10:33:27.250+03:00You're probably hearing electrical interferenc...You're probably hearing electrical interference caused by the door motor. AM radio is very sensitive to motor noise.Oona Räisänenhttps://www.blogger.com/profile/08764440174916554983noreply@blogger.comtag:blogger.com,1999:blog-5096278891763426276.post-44612035560505311332014-10-23T22:12:50.943+03:002014-10-23T22:12:50.943+03:00Hi Ms Oona- I had a similar mystery yesterday taki...Hi Ms Oona- I had a similar mystery yesterday taking our local bus on public transit. Listening to my AM/FM headphones I noticed on AM radio, every time the door to the bus is opened and only the FRONT door, a signal that sounds like a fast siren interferes with AM radio. I thought that was interesting. I wonder if a signal is sent back to the head office to note each time a door is opened?Kristin Bnoreply@blogger.comtag:blogger.com,1999:blog-5096278891763426276.post-28427481368820862572014-06-09T07:20:46.092+03:002014-06-09T07:20:46.092+03:00Hello Oona,
I found a similar case (this time a Po...Hello Oona,<br />I found a similar case (this time a Police helicopter) and tried to replicate your excellent work. I could not easily demodulate in software, so I used minimodem. <br /><br />Congratulations for the very interesting blog!<br />Alain K1FMAlain De Carolishttps://www.blogger.com/profile/05152086160028044702noreply@blogger.comtag:blogger.com,1999:blog-5096278891763426276.post-49398775551389899632014-05-21T08:29:47.215+03:002014-05-21T08:29:47.215+03:00Here's an example envelope detector for two pi...Here's an example envelope detector for two piped inputs: <a href="https://github.com/windytan/darcdec/blob/master/env.c" rel="nofollow">env.c</a>Oona Räisänenhttps://www.blogger.com/profile/08764440174916554983noreply@blogger.comtag:blogger.com,1999:blog-5096278891763426276.post-74974411138596966212014-05-20T23:45:21.185+03:002014-05-20T23:45:21.185+03:00Take the filtered signals, run any kind of envelop...Take the filtered signals, run any kind of envelope detection, and then just use basic inequalities, "bit = (mark > space)".<br /><br />It is oftentimes the case that the higher frequency in BFSK is the mark frequency (1). If it isn't, decoding will fail and I can try the other way roundOona Räisänenhttps://www.blogger.com/profile/08764440174916554983noreply@blogger.comtag:blogger.com,1999:blog-5096278891763426276.post-48565994020056487582014-05-20T22:23:19.536+03:002014-05-20T22:23:19.536+03:00Hi Oona,
Very impressive signal decoding. I'm...Hi Oona,<br /><br />Very impressive signal decoding. I'm fairly new to LInux, and to SoX, but I'm trying to recreate your decoding of the GPS location data from the YouTube video, as an exercise in learning. <br /><br />With respect to the decoding of the BFSK 1.2kHz and 2.2kHz signals representing the binary data, how did you compare the two sinc filtered signals to create your baseband digital bitstream?<br /><br />And also, how did you decide which frequency (of 1.2kHz and 2.2kHz) represented a binary 0 and which a binary 1? <br /><br />Many thanks, and keep up the interesting work and posts,<br />Oli, from Fleet, UK.<br />Olihttps://www.blogger.com/profile/02826970553148017807noreply@blogger.comtag:blogger.com,1999:blog-5096278891763426276.post-6552253783386488032014-05-20T17:19:20.836+03:002014-05-20T17:19:20.836+03:00You should look at APRS using Ham radio. It is com...You should look at APRS using Ham radio. It is completely legal (if you have your licence) and has already been developed. :)Joseph Thomashttps://www.blogger.com/profile/16863821702478782975noreply@blogger.comtag:blogger.com,1999:blog-5096278891763426276.post-87729947206591572162014-04-02T06:00:53.447+03:002014-04-02T06:00:53.447+03:00Sorry, I meant "the timestamp of each data pa...Sorry, I meant "the timestamp of each data packet."Timothynoreply@blogger.comtag:blogger.com,1999:blog-5096278891763426276.post-91826015092326010902014-03-31T20:49:59.553+03:002014-03-31T20:49:59.553+03:00You're welcome. When I decoded it in a Matlab ...You're welcome. When I decoded it in a Matlab script I wrote, I took care to preserve the timestamp of the beginning of each timestamp.Timothynoreply@blogger.comtag:blogger.com,1999:blog-5096278891763426276.post-88948406054243844852014-02-14T13:51:20.042+02:002014-02-14T13:51:20.042+02:00Thanks for the kml file, Timothy. With that it sho...Thanks for the kml file, Timothy. With that it should be possible.<br />How did you manage to obtain the timing info?Anonymoushttps://www.blogger.com/profile/09970205369659284743noreply@blogger.comtag:blogger.com,1999:blog-5096278891763426276.post-73915254231458599452014-02-10T15:49:16.768+02:002014-02-10T15:49:16.768+02:00wow, this is so cool. I love when you post article...wow, this is so cool. I love when you post articles like this. it inspires the inner geek within me. Unknownhttps://www.blogger.com/profile/05646418743549381044noreply@blogger.comtag:blogger.com,1999:blog-5096278891763426276.post-44551045500023407002014-02-08T16:37:24.398+02:002014-02-08T16:37:24.398+02:00See the first sentence of the post, there's a ...See the first sentence of the post, there's a link.Oona Räisänenhttps://www.blogger.com/profile/08764440174916554983noreply@blogger.comtag:blogger.com,1999:blog-5096278891763426276.post-42696439884315639192014-02-08T12:14:35.474+02:002014-02-08T12:14:35.474+02:00http://www.fileswap.com/dl/5lJeEkIc3D/HelicopterCh...http://www.fileswap.com/dl/5lJeEkIc3D/HelicopterChase.kml.html<br />Each point's title is the seconds into the video (minus 0.185), and the description is the elevation value.Timothynoreply@blogger.comtag:blogger.com,1999:blog-5096278891763426276.post-30527612156345069582014-02-08T03:04:02.924+02:002014-02-08T03:04:02.924+02:00Look up APRS for more information on the Ham radio...Look up APRS for more information on the Ham radio system that is very similar to this. Sending your location speed heading and other infomation in about a .7 second burst every x number or minutes. <br /><br />Jim K5JSWJimhttps://www.blogger.com/profile/13966635958496339714noreply@blogger.comtag:blogger.com,1999:blog-5096278891763426276.post-77157081060207534712014-02-07T16:43:31.531+02:002014-02-07T16:43:31.531+02:00Say, Oona- you sound a lot like me (with your curi...Say, Oona- you sound a lot like me (with your curiosity on things you hear and figuring out the signals) for reference, could you post the youtube video you finagled the signal from if possible? If you were signed into youtube when you watched it, it would be in your watched list. It would be interesting to see the very video you suspected that sound from. Thanks in advance- KristinAnonymousnoreply@blogger.com