@blinry Some chinese knock-offs have a direct sampling input, allowing reveption below 50MHz (like higher priced ham radio HF receivers have, albeit those in muuch higher quality). With that you could try identifying HF noise like from solar power converters. With a directional antenna (a simple loop often is sufficient) you could try and track down the source.
@blinry
check the
rtl_433
program. Quite a number of radio-connected weather sensors and(!) tire pressure sensors can be monitored with it (at 433MHz, obviously).
Aside from humidity and temperature (weather) and tire pressure and temperature you can also monitor coming and leaving of neighbors, if you note down which sensor belongs to which car. Note that tire pressure sensors send every few seconds when active and slow down to a couple of times a day when not in use.
This is a special frequency range in Germany: Anyone is allowed to send there, using licensed devices. There are 6 channels.
I think someone's testing their device there right now. :D I heard a "Hellooo?", then a "Test, test", and then a "General call to all stations". Oh, and just now a short transmission on channel 3 in a Slavic-sounding language!
Freenet devices have a range of only a couple of kilometers, so these people must be pretty close! :O
@blinry especially because you see the spectrum around it dropping, while you don't have any AGC configured. That means that the signal is soo powerful that it's actually overloading/saturating your receiver. They must be really close.
(or you just fiddled with the gain setting while you received that... :P)
@blinry Ha! Yesterday evening - after some months of them idling around, I cleaned up my stock of Quansheng and Baofeng radios, configuring to a common freenet frequency as a sane default that works well with the retrofitted antenna doing a lot of "Hello"ing and "test test test"ing :D
But likely far outside of your reception area.
@nblr@blinry Just to tease more people outside of the hobby: "range" is a weird thing if you have an atmosphere to deal with :) You can get troposphere ducting and receive UK broadcast radio in Poland for example. But the conditions are more probable over a body of water. See https://dxinfocentre.com/tropo_eur.html
Also if you aim your antennas right you can bounce signals off commercial airplanes*.
While browsing the aviation frequencies, I found this station that reports weather conditions in an endless loop. It seems to be the "Automatic Terminal Information Service" of Hamburg airport!
Thanks to that, I now know that the current air pressure is 1011 hPa! :D
Listening to "messages not meant for the general public" is not allowed in Germany, so of course I didn't do that. And if I had accidentally done that, I wouldn't be allowed to tell you about it. 🙅
@dingens@blinry afaik all german neighbour countries allow it, meaning if you step one foot over the vorde you could just listen to German ATC :neocat_woozy:
How stereo audio is transmitted is really interesting, because it's backwards-compatible to receivers that don't support it:
Here, you see the demodulated audio frequency spectrum. Below 19k Hz, it's just mono audio. Then, to mark a stereo station, there's a constant "pilot tone" at 19k Hz! (Outside of what most humans can hear.)
Then, if you double the frequency of the pilot tone, you can derive the sections where the left & right channel is transmitted!
@blinry IIRC not quite: After the pilot tone it's not left and right individually but the difference (L-R). Because (L+R)+(L-R) equals 2L and (L+R)-(L-R) equals 2R :)
If you triple the frequency of the pilot tone, you get to a range where FM stations transmit small amounts of digital metadata, like the name and genre of the station, and the current song! That's a protocol called Radio Data System.
This system can also transmit road traffic information! There seems to be a road closure at "0x64BE". The Federal Highway Research Institute publishes an Excel table, where I could look up that this is a town in Lower Saxony!
8: Listen to conversations on the 2-meter amateur radio band
This is a frequency range reserved for amateur radio operators – for non-commercial use only. You may send on this band after getting a license.
What I found here is seemingly a conversation circle facilitated by a relay around 15 km away from here – it takes input on a certain frequency, and outputs an amplified copy of it on another frequency! Klaus, Bernd, Jürgen and Horst are talking about antennas, relays, and Windows XP! 😁
With that, I end the first day of SDR experiments! :) It's amazing to me how much invisible communication is going on around us in the electromagnetic spectrum at the same time!
To be continued tomorrow. Feel free to suggest things I could receive!
@blinry all kind of 433 MHz gadgets, try rtl_433: https://github.com/merbanan/rtl_433 - why buy your own outside weather station if you could just use all your neighbors’?
@blinry Take a look at 433MHz, there are a lot of simple devices like switchable sockets, home weather stations, car tire pressure sensors that use that band. Also take a look at wM-Bus at 868MHz used by watermeters, smoke detectors, etc.
@blinry speaking of sensors, there's also the wmbus protocol used by wireless utility meters (water, heating etc.) I have these meters in my flat and bought a sdr stick to integrate their readings into my @homeassistant : https://github.com/wmbusmeters/wmbusmeters
They send out their status using AIS (Automatic Identification System). And again, I receive a lot of them here in Hamburg! :O
I was especially excited to receive data from @msstubnitz (a fisher boat that was turned into a culture center/techno club)! It reports its status as "moored", and its speed as 0.1 knots! :D
This is again the software SDRangel. Apparently, it can also display a 3D map, but I haven't figured out how to add 3D models…
I was curious whether you could tell if someone used their phone!
So I borrowed a GSM phone, tuned to the correct frequencies, and made some test calls.
What surprised me most: You can kind of "see" the volume at which I was talking!?
In the recording, the three dense bands at the end were when I was humming into the phone at the other end. This only worked in the "receiving" direction.
The program gpredict is really nice to find out when satellites will pass overhead! Learned lot yesterday, including that one satellite I was trying to receive burned up last week! :D
I was super excited when I first received a signal from a NOAA satellite! 🛰️
But I didn't manage to decode it properly yet. Maybe my reception is too noisy? I wanna keep trying, but I gotta move on.
@blinry i bought a flpper zero with little to no prior knowledge and enjoy this thread so much. i think about bying an sdr now, but i don't think i'd find the time to proper play around with it...
In Germany, the police has switched to an encrypted digital protocol called TETRA.
Even though I've seen some interesting talks at CCC events about weaknesses in the decryption, all I wanna do for now is look at the pretty signals in sdrpp. :3
Some of the most fun I'm having is just browsing frequencies and seeing what I can find!
Sometimes, I encounter signals I can't identify.
For example, at 865-868 MHz, there's a family of slow, continuous, digital signals that make a nice melody when listened to in single-sideband demodulation!
And at 177-180 MHz, there's two very broadband transmissions. Might be TV? But I can't find out what type.
If you have ideas, let me know! :) Time for lunch!
@blinry Shamelessly hijacking your thread… but bearing a nice spectrum graph while doing so!
Does anyone know what this one in the upper region of 800MHz might be?
@blinry if I remember correctly the 868 MHz range is used for the same types of devices as the 433MHz, free to use by anyone for short range devices. Might be a baby monitoring device or something similar. I might be mistaken but I think I've seen PMR style walkies using said frequencies
@blinry I was going to say LoRa including stuff like MeshStatic or Reticulum . Curious whether the melody is an actual intentional melody or just sounds like one ?
@blinry If you have a portable radio that can tune to the signal - go for it. :D (or use a lot of sticky tape to make a portable SDR laptop with a dipole?)
Even if other sonde hunters get to it first I'm sure they'll be happy to let you take photos of the sonde itself to promote radio.
According to https://sondehub.org/# it will fall somewhere close to Sandesneben around 14:00. But it's just a prediction.
Edit: I read the timestamp wrong, it's 14:00 not 15:00.
So, the full story: I made my way up to the landing site by subway, train and bike.
As I circled the site, I encountered a person in their 60s, with a stubbly beard and a blue wool hat. He was looking in the direction of the crash site, and was holding a smartphone, so I asked him whether he also was looking for the radiosonde.
He was! We looked for it together for half an hour, jumping over small rivers and crawling through the woods, while he gave me a lot of tips related to hunting sondes.
He told me that he had found around 40 of them so far!
Usually, the sondes keep broadcasting after landing, but this one wasn't. So he quickly guessed that someone else could've taken it. Or maybe it landed in the water and died?
Eventually, we gave up, and walked back to our vehicles. He also is an amateur radio operator, and could answer a couple of questions related to building antennas!
In the 2-meter amateur band, there are certain frequencies for the "Automatic Packet Reporting System". It's a bit like IP – packets have a "from" and a "to". They can also broadcast their position, or weather data.
Some stations seem to announce themselves as repeaters, which probably help forward the packets to increase the range.
And two people seem to be on a "fieldday", and broadcast their location. :D
People on the Internet say that there are many problems with this – that it would be better to have it outside, and that there's an impedance mismatch between the receiver and the wire.
I could address those problems, but I wanna try how well this works first :)
The German Weather Service broadcasts maritime information throughout the day on various shortwave frequencies.
They use a protocol called RTTY (radioteletype), and it took me a while how to decode it. But I found a neat little program called "fldigi": You can pipe audio to it, and then if you pick the correct settings, it happily transcribes the messages!
Here's the station weather reports for the Baltic Sea and Northern Sea!
I found some other strange signals on the 30-meter band. The Signal Identification Wiki was really helpful for figuring out what they were: https://www.sigidwiki.com/wiki/FT8
FT8 is a new protocol, invented in 2017, and it seems to be super popular right now! It allows you to transmit short messages, and again, people are looking for people to talk to (CQ), saying how well they receive each other, or saying goodbye (73).
In the low frequencies, occasionally, you can hear a short chirp! :D These are caused by ionosondes, scientific instruments which measure the properties of the ionosphere by sweeping a wide frequency spectrum.
Another signal (which I accidentally got in the same screenshot) is a radar system – in this case, according to the Signal Identification Wiki, it's a "CODAR" system, used to measure the motion of water waves and currents along coasts! :O
How do you transmit speech over long distances? You can use "amplitude modulation", where you change the volume of the carrier frequency to model your audio.
As a side effect, the bands to the sides of the carrier will contain a signal, as well.
One trick is to transmit just those sidebands, which saves power! But you have to "guess" the base frequency when listening.
SDR++ makes it very easy to play with this! :) Here's someone from Serbia!
28: Listen to AM radio from the other side of the world
At night, low-frequency radio waves can travel further around the world, because they're reflected by the layers of the ionosphere! There's something magical about this.
I put my antenna outside, and I can hear a lot of broadcasting stations! On https://www.short-wave.info, you can look up where they are located.
Some stations in China are broadcasting with very high power! Some are over 7500 km away.
After I looked into the low frequencies yesterday, let's go to a higher band again: The Citizens Band!
This is the third frequency band I'm aware of where anyone is allowed to transmit – provided that you use a licensed device!
This is a band where my random wire antenna really comes in handy. Without it, I would have a hard time understanding anything. And even with it, transmissions are extremely noisy.
CB radio is used internationally, especially by truck drivers?
30: Assess the propagation of radio waves using beacons
The International Beacon Project runs a network of 18 stations, which take turns transmitting their callsigns at certain frequencies.
Using this system, you can quickly get a sense of how well radio waves are currently propagating to your location. Clever!
I picked up the beacon from southern Finland! You can see its callsign scrolling away in the video. It's followed by four dashes send with decreasing power. I only heard the first one…
I would've loved to receive DCF77, which powers the radio clocks in Germany! But no matter how hard I listened to 77.5 kHz, there was nothing there. I don't think my dongle can do that.
So let's use higher frequencies! Russia transmits its "RWM" time signal at 9996 kHz, which beeps every second, with a long beep for the full hour.
Not enough to tell the time, but enough to adjust your wrist watch, I guess!
@blinry Huh, that's really neat! How did you calculate it's real speed? I think there's a few nice bits of geometry involved, assuming you're stationary on the ground while recording the signal. I might have to try this too when I get time!
So I tuned into the next frequency that was listed, and: Bingo!
Allegedly, this is a station in Moscow. Today, it sent "218, 218, 218" in a loop, followed by three long beeps, which is the format of a "null message".
@blinry is your list already pre-defined?
otherwise: Download WSJT-X and try to decode some WSPR or FT8. I wonder how "far" (in terms of distance) you can hear :)
This was a bit like trying to catch a rare insect! 🐛
LoRaWAN is a low-power, wide-area networking protocol, intended for "Internet of Things" applications.
You can see transmission in the lower half of the screenshot! It has a very cute structure: You can see eight "down-chirps", followed by two "up-chirps". That's the header, followed by the payload.
To look for the signal, I made a "baseband capture" in SDR++, and opened the recording in sonic-visualizer.
This week is really intense for me. Initially, I thought I'd do 10 things per day, but it turned out that that's too much. I have to learn so many new things.
Many things I try don't work on my first attempt. Finding LoRaWAN, decoding packet radio, finding something on PMR446, decoding the satellite – those were all things that required a second (or third) attempt.
This project is exhausting, but also joyful – having committed to it, I get in a nice flow state, where I can focus on it for hours.
Often, I think: "Okay, this is it. I can't possibly find more things." But this is the power of the 50 Things technique: I have to keep looking, leave my comfort zone, be creative, try things I otherwise wouldn't have tried!
So, 11 more things, huh? If, after reading this thread, you have suggestions for more things to receive/decode/try, let me know! 😬
@blinry
You might try to get a navigational signal from an ILS or VOR or NDB. I haven't done it myself, but I can assist you if you need further information.
you could look at HAMNET, a amateur radio pager network, with POCSAG1200, not sure if there's a transmitter near you, though.
there's also this digital short wave radio thing called "DRM", "Digital Radio Mondiale". IIRC there's a Windows tool to decode it. Has some fancy graphics for signal constellation, etc.
@blinry The only thing I can think of that I didn't see you explicitly cover yet (although you had one in your rtl_433 screenshot) are TPMS signals: tire pressure monitors from cars. They usually carry unique IDs and can be used to identify individual cars from around the neighborhood.
@blinry Do combinations of the things you already did count? I think SSTV postcards from ISS are a thing.
There also a whole world of amateur digital radio (DMR, D-Star repeaters).
Or the amateur radio pager network https://www.hampager.de/#/ those seem legal to listen to and decode for the purposes of experimentation. But of course require judgement before posting to the public Internet.
The chips in my SDR stick are also being used in DVB-T dongles!
So, can we watch TV? Unfortunately, no.
From what I pieced together, there's a difference between using the stick in SDR mode (where it sends the full spectrum), and in TV mode (where it sends the decoded video).
In Germany, there's now DVB-T2, which my hardware don't support in TV mode.
And in SDR mode, the bandwidth is too narrow for DVB-T2.
But we can scroll over a channel and look at it! :3
Did a little walk to a big intersection, to see what "device signals" I'd find there at 433 MHz.
I could confirm that the IBIS beacons are in fact being sent by buses! The included "vehicle ID" even matches the white number that's printed on it.
I also saw some messages from tire pressure monitoring systems in cars! They also include an ID, and usually, the brand of the car! The owners probably aren't aware how easy it would be to track them… (Thanks, @scy!)
@blinry
If the receiver is sensitive enough, and if you have a directional antenna of some sorts, you could try to see if you can detect the difference in the noise floor coming from the sun vs the clear sky!
But maybe that is hard to do in as a noisy RF environment as most urban places are...
@blinry as far as I know the ISM band goes from 433.05 MHz until 434.79 MHz, so this is in the range…? I guess there are also some kinds of "channels" defined on it when you want to have different applications using it at the same time
@daniel_bohrer Mh yeah, I meant that that li'l signal in the screenshot seems to change frequencies while its sending! Maybe some emitter is heating up or something?
So I caught a satellite again! :D This time, it's a school project, the Italian satellite "Max Valier". It continuously sends Morse code on a beacon frequency.
Pretty weak signal, but here's what I could hear:
"3MV MAX VALIER SAT ... MANFRED ES CHRISTA FUKSE 73 ... II3MV ..."
Super happy about this! I got both the name of the satellite, as well as its callsign at the end, and what seems to be some kind of greeting?
This is another thing that's not allowed in Germany, so you shouldn't do it.
Pagers use a format called "POCSAG" (Post Office Code Standardisation Advisory Group…), which you should not decode using multimon-ng.
Because you would find that the content is short and cryptic anyway. It would probably be repeated by several stations all around you, to make sure the whole region is covered.
Do not read the English Wikipedia page! It contains frequencies!
@blinry oder der Klassiker zu dem Thema, man tauscht einen Teil seiner Freizeit gegen ein neues Hobby ein und bekommt dann sogar einen Decoder dafür. Inkl Erklärung was es bedeutet ;)
There are ground stations that emit a signal that allow calculating your angle relative to it! If you receive two, you can determine your position.
I hear the one close to Hamburg! SDRangel has a decoder, of course! It outputs angles between 210° and 230°, which is pretty good! Don't think they are meant to be used from the ground.
I spent ages trying to build my own decoder in GNU Radio. But I wasn't familiar with it at all, and I eventually gave up. Still, that seems to be the software you wanna learn for tasks like these!
By the way, how the ground stations work is fascinating: In my case, it's a "Doppler VOR": It transmits a static frequency via amplitude modulation, and adds another signal that moves around in circles, so you get a Doppler frequency shift.
If you compare the two, you can calculate the angle!
47: See how low you can go in the frequency spectrum
This was a fun exploration: What's the lowest-frequency broadcast I can receive?
The RTL-SDR Blog V4 stick I'm using has a neat feature – a built-in "upconverter", which is enabled automatically when you try to listen to frequencies below what the chipset supports. This allows it to receive down to ~500 kHz!
The first stations that are comprehensible start at 1 MHz for me.
48: See how high you can go in the frequency spectrum
My SDR stick has a maximum sampling rate of 3.2 megasamples/s, so by Nyquist's theorem, that means that the highest frequency it can theoretically measure is 1.6 GHz.
It seems pretty quiet up there, probably because I lack proper antennas. I found these three lines in an amateur band, but they probably originate from the stick itself, or another device.
So the highest-frequency thing I've received is ADS-B at 1090 MHz (see entry #5)! 🎉
@blinry Uhh, that works a bit different for SDRs. The maximum possible bandwidth for 3.2MS/s is actually 3.2 MHz, this is because each sample is actually 2 samples! One I sample and a Q sample, with the same signal as the I part, but phase shifted by 90°.
(and then it‘s MHz, not GHz)
The maximum frequency is set by the capability of the tuner IC in front of the RTL2832, the type of tuner dictates the maximum (and minimum) frequency.
@blinry@manawyrm
Yep, you can think of it like tuning into a channel on the radio and then listening to the music.
The higher your tuner/mixer freq. goes, the higher the station frequency you can tune into, meaning you can explorer more spectrum with the SDR.
The higher your sampling rate, the higher the bandwidth of the station you can listen to, meaning more data/music fidelity/etc at once.
@blinry
Yes please, for a blog post : having a primer for all you did on an easily bookmarkable page would be most welcome.
For me, especially if it contains like a "quick start" to how to do each of the 50 things : softwares, frequencies, settings, command lines, antenna sizes, etc.
So, was this project in fact a gateway drug to getting an amateur radio license?
Yeah, probably. I'd love to transmit something and experiment more! :D
In Germany, a new license class will be introduced this summer, that'll allow you to send on the 10-meter, 2-meter and 70-cm bands (the "N class").
In fact, there's a really good online course that teaches you everything you need to know: https://50ohm.de Highly recommended, even if you're not planning on getting a license.
@blinry great thread! :awesome:
these things are relativley cheap for the features you get 👌
the best option if you don't have a license like me; and even if you dont have such a device there are many great sites to try if you want to get into SDRs
@blinry VOR stations are indeed not meant to be used from the ground. When learning to fly planes (PPL course), we even learn the formula linking beacon range and aircraft altitude: range in NM = 1.23 × sqrt(altitude in ft).
So being at 12 NM from the VOR, you're supposed to be at least 100 ft (~30 m) high to be reasonably sure to receive the signals.
@blinry are you planning on doing a writeup of these in "long-form"? Like, a blog or something?
Reading through this makes me want to try a lot of it with my SDR, which I use almost exclusively for testing amateur radio equipment, but which is begging to be put to better use.
Oh, good question! For receiving satellites, I'm using the dipole antenna that came with the kit, extended to 53 cm per side, in a V-shaped configuration, pointing north.
I attached it to the outside of my window using the suction cup that came with it!
@blinry I think you should be able to get APT transmissions from NOAA-16 with that antenna. was gonna recommend to you that you should try capturing LRIT/HRIT from GOES but you'll need a different antenna setup and an additional LNA. future project maybe :P its fun!
As #Morsecode is rather slow, its practitioners have always used many abbreviations.
There are quite a few of them. Those, plus a rather limited set of select English words, enable two stations to exchange quite a bit of small talk: Introducing each op's name, location, basic info about local weather, and briefly introduce your station - all without knowing a common language.
"es" is short for "and", and "73" is the customary greeting at the end of a contact.
@blinry@scy
Interesting. I'm assuming the batteries (that i recently paid to replace! ) on these tires' ISB transmitters can't be large and last years so the transmitted power must be quite low, and thus range fairly short.
@blinry@scy afaik these beacons are / were used for Vorrangschaltungen in Hamburg - If I remember correctly sb even built a contraption to mimic the signals to turn their traffic lights green
@blinry This must be the best thread ever 😁. You should pack it into a blog post outside fedi when finished. Btw, how do you know the origin of the transmissions? For instance, how do you know this comes from Russia?
@blinry ARISS does do some SSTV from the ISS from time to time. That's always fun to go outside, wait for the ISS to pass overhead (bonus points if you can see the bright dot in the sky <3 ) and then try to catch and decode as much as you can. https://www.ariss.org/http://ariss-sstv.blogspot.com
@blinry i think the typical rtl dongle goes down to 25 Mhz. Using directly sampling u get down to 500kHz or 100kHz. I don't think u could reach dcf77 with a typical rtl dongle
@blinry in the 90s we used it instead of jitsi to chat in the evening. A handful of people had big antennas on the roof in our small village. That was fun. Oh and you had to learn the Q-codes 😅
@blinry Seriously, if I wasn't still avoiding sitting at my desk too long because it still hurts, following this thread I'd already gotten my own SDR dongle out and started playing with it again 😄 Awesome stuff!
At this point, I caught a LoRaWAN message, see entry number 38! The other signals are still there, constantly, and I still don't know what they are! The LoRa messages are more infrequent, less strong, and on other frequencies.
@blinry It’s quite a journey you’ve taken here! I must try some more of the software you’ve mentioned - I use an SDRplay RSP-1A with a PA0RDT Mini-Whip active antenna http://dl1dbc.net/SAQ/Mwhip/Article_pa0rdt-Mini-Whip_English.pdf There’s so much out there… have you considered an amateur license? I mostly transmit FT8, worldwide contacts with low power and wire aerials.
@blinry Is it really the volume or just speaking/listening? Maybe GSM is half-duplex with noise gate or something? I think @chaosvermittlung said some phone connections are half-duplex.
I'm not quite sure if your SDR can handle these kind of low frequencies. The rtl-sdr.com ones have the "direct-sampling" hack for HF, but I'm very unsure how well it'll perform for such low frequency stuff.
@blinry A correction to your graph: The stereo information is actually a dual-sideband signal and does carry the difference compared to mono signal (L-R). The LSB and USB in the decoded FM spectrum do not represent left and right channels.
The left channel is mono plus difference (L+R)+(L-R) and right channel is mono minus difference (L+R)-(L-R). https://en.wikipedia.org/wiki/FM_broadcasting#/media/File:RDS_vs_DirectBand_FM-spectrum2.svg
@blinry #ATIS-broadcasts contain more than only the local weather. They also give you a hint which runway(s) to use and some additional operational data, hints about bird activity etc.
There are telephone numbers for some airports, so if you happen to miss your RTL-SDR you can still get the information. E.g. Frankfurt: +496969049188
@blinry
Note : when listening, there are usually options to use lowpass/highpass filters to remove the white noise. I highly recommend it for long period of listening ;)
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