{"id":13053,"date":"2025-09-16T20:12:03","date_gmt":"2025-09-16T20:12:03","guid":{"rendered":"https:\/\/usaontheweb.com\/clone1\/fifty-things-you-can-do-with-a-software-defined-radio\/"},"modified":"2025-09-16T20:12:03","modified_gmt":"2025-09-16T20:12:03","slug":"fifty-things-you-can-do-with-a-software-defined-radio","status":"publish","type":"post","link":"https:\/\/usaontheweb.com\/clone1\/fifty-things-you-can-do-with-a-software-defined-radio\/","title":{"rendered":"Fifty Things you can do with a Software Defined Radio"},"content":{"rendered":"<p>Software <\/p>\n<div>\n<p>Last week, I went on an adventure through the electromagnetic spectrum!<\/p>\n<p>It\u2019s like an invisible world that always surrounds us, and allows us to do many amazing things: It\u2019s how radio and TV are transmitted, it\u2019s how we communicate using Wi-Fi or our phones. And there are many more things to discover there, from all over the world.<\/p>\n<p>In this post, I\u2019ll show you fifty things you can find there \u2013 all you need is this simple USB dongle and an antenna kit!<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/ed1513b2b350229a.jpeg\" alt=\"software The device looks like a big USB stick with a bronze screw connector at the back end. It's labelled \"RTL-SDR Blog V4\".\" title=\"software The device looks like a big USB stick with a bronze screw connector at the back end. It's labelled \"RTL-SDR Blog V4\".\"><\/p>\n<h2 id=\"the-make-50-of-something-technique\">The \u201cMake 50 of Something\u201d technique<\/h2>\n<p>A couple of years ago, I heard about the \u201cMake 50 of Something\u201d technique in Vi Hart\u2019s Fifty Fizzbuzzes. Since then, I\u2019ve already made fifty programs for the fantasy console TIC-80 in one weekend in 2021.<\/p>\n<p>I found that a very exciting experience \u2013 trying to make so many new things really pushed me to leave my comfort zone, to be creative, and not to get sucked into rabbit holes too deep.<\/p>\n<p>I knew I definitely wanted to try the technique again. So, when I took a week of vacation, I decided to try to find 50 things to do with a Software Defined Radio!<\/p>\n<h2 id=\"what-is-an-sdr\">What is an SDR?<\/h2>\n<p>A Software Defined Radio is essentially a radio that relies on a computer to do most of its data processing. It doesn\u2019t rely on analog hardware too much \u2013 instead, most of what is does is \u201cdefined in software\u201d, hence the name.<\/p>\n<p>Usually, SDRs can detect electromagnetic waves in a much wider range than a common FM radio, which makes it especially exciting! I got interested in SDRs after reading about Albert\u2019s project to build one as a module for the Framework laptop!<\/p>\n<h2 id=\"what-youll-need\">What you\u2019ll need<\/h2>\n<p>I went into this week without much knowledge of the things I\u2019d find. I\u2019d read through a introductory course for aspiring amateur radio operators (more on that later), but I barely knew which way to point my antenna.<\/p>\n<p>If you want to follow along, this section is intended to help you get started!<\/p>\n<p>Most of the 50 things also have a little infobox at the beginning, explaining the frequencies, and some special knowledge needed to receive them.<\/p>\n<h3 id=\"hardware\">Hardware<\/h3>\n<p>I looked into the topic a bit, and a popular, cheap SDR right now is the <em>RTL-SDR Blog V4<\/em>, which has the form factor of a simple SUB dongle. You can get it for around $30, or as a kit with telescopic antennas for $50.<\/p>\n<p>Everything I tried during this week was done using this USB dongle, the antenna kit, and a long piece of wire!<\/p>\n<p>(By the way, there\u2019s another great option if you don\u2019t want to buy anything \u2013 lots of people make their SDR accessible through the Internet! You can find a map here.)<\/p>\n<h3 id=\"using-the-antennas\">Using the antennas<\/h3>\n<p>I tried to adjust my antenna to the desired frequencies as best as I could. I think for receiving, it\u2019s not super important that your antenna is perfectly configured, though.<\/p>\n<p>For most applications, I used the dipole antennas that came with the kit I purchased. Dipole antennas have two sides that stick out the same length. You generally wanna make the whole antenna half as long as the wave length you want to receive, and orient it vertically.<\/p>\n<p>My rule of thumb was to divide 72 by the frequency in MHz, and take that as the length of each side of the dipole in meters. That\u2019d make the whole antenna a bit shorter than half of the wavelength.<\/p>\n<p>For example, this is what the configuration looked like for frequencies around 100 MHz:<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/e7c6048323389ceb.jpg\" alt=\"software A 1.4 m long, two sided antenna, attached to my window.\" title=\"software A 1.4 m long, two sided antenna, attached to my window.\"><\/p>\n<p>And for higher frequencies, I used the tiny screw-on antennas from the kit:<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/6476ab30f0d233df.jpg\" alt=\"software The antennas are only a couple of centimeters long.\" title=\"software The antennas are only a couple of centimeters long.\"><\/p>\n<p>For specific applications like receiving satellites, or receiving locators for airplanes, I used special configurations, but I\u2019ll discuss these as we go!<\/p>\n<h3 id=\"software\">Software<\/h3>\n<p>The software I liked best, and which I used for many things, was SDR++. It allows you to explore the frequency spectrum very smoothly, and has a modern user interface!<\/p>\n<p>But I also used plenty of other software, on Linux in my case. I\u2019ll link to the software as needed below.<\/p>\n<h2 id=\"monday\">Monday<\/h2>\n<p>On Monday morning, I was excited to start this project! I sat down at my desk, and got to work!<\/p>\n<h3 id=\"listen-to-fm-radio\">1: Listen to FM radio<\/h3>\n<ul>\n<li><strong>Frequency:<\/strong> 87.5-108 MHz<\/li>\n<li><strong>Modulation:<\/strong> FM (\u201cfrequency modulation\u201d)<\/li>\n<\/ul>\n<p>This as an obvious first thing to do, as the signals are very strong! I was using the SDR++ software, and it felt very nice browsing around and discovering the stations around me! It reminded me of exploring the radio as a child.<\/p>\n<p><video src=\"http:\/\/blinry.org\/545dc74004d1946b.mp4\" controls><\/video><\/p>\n<p>I found a local station that gives 1-hour slots to civic groups, for example!<\/p>\n<h3 id=\"listen-to-freenet\">2: Listen to Freenet<\/h3>\n<ul>\n<li><strong>Frequency:<\/strong> 149.01-149.11 MHz<\/li>\n<li><strong>Modulation:<\/strong> FM<\/li>\n<\/ul>\n<p>This is a special frequency range in Germany: Anyone is allowed to send there, using licensed devices. There are 6 channels.<\/p>\n<p>I think someone was testing their device there when I listened in. \ud83d\ude00 I heard a \u201cHellooo?\u201d, then a \u201cTest, test\u201d, and then a \u201cGeneral call to all stations\u201d. Oh, and shortly after a short transmission on channel 3 in a Slavic-sounding language!<\/p>\n<p>Freenet devices have a range of only a couple of kilometers, so these people must have been pretty close! :O<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/99dc224db1441231.png\" alt=\"software A short burst in the waterfall diagram, at 149.05 MHz.\" title=\"software A short burst in the waterfall diagram, at 149.05 MHz.\"><\/p>\n<h3 id=\"receive-weather-conditions-from-airports\">3: Receive weather conditions from airports<\/h3>\n<ul>\n<li><strong>Frequency:<\/strong> Differs by airport, search term is \u201cATIS\u201d<\/li>\n<li><strong>Modulation:<\/strong> AM<\/li>\n<\/ul>\n<p>While browsing the aviation frequencies, I found this station that reports weather conditions in an endless loop. It seems to be the \u201cAutomatic Terminal Information Service\u201d of Hamburg airport!<\/p>\n<p>Thanks to that, I found out that the current air pressure was 1011 hPa! \ud83d\ude00<\/p>\n<p><video src=\"http:\/\/blinry.org\/ecdd3c2ce2b8da7b.mp4\" controls><\/video><\/p>\n<h3 id=\"listen-to-airplane-communication\">4: Listen to airplane communication<\/h3>\n<p>Listening to \u201cmessages not meant for the general public\u201d is not allowed in Germany, so of course I didn\u2019t do that. And if I had accidentally done that, I wouldn\u2019t be allowed to tell you about it. \ud83d\ude45<\/p>\n<h3 id=\"track-aircraft-via-ads-b\">5: Track aircraft via ADS-B<\/h3>\n<ul>\n<li><strong>Frequency:<\/strong> 1090 MHz<\/li>\n<li><strong>Protocol:<\/strong> ADS-B<\/li>\n<\/ul>\n<p>That\u2019s short for \u201cAutomatic Dependent Surveillance \u2013 Broadcast\u201d. Aircraft send it automatically to be tracked.<\/p>\n<p>For this, I built my first antenna! From wire and and an antenna connector called \u201cSMA\u201d.<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/abc2bb1af1132f58.jpeg\" alt=\"software A antenna made from two short wires.\" title=\"software A antenna made from two short wires.\"><\/p>\n<p>And it worked! o\/ I decoded the signal using the software SDRangel. Fascinating! I saw some big &#038; small airplanes, and even a helicopter!<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/0e508ca1be070861.png\" alt=\"software Planes around Hamburg on a map, together with a table of their properties.\" title=\"software Planes around Hamburg on a map, together with a table of their properties.\"><\/p>\n<h3 id=\"listen-to-stereo-fm-radio\">6: Listen to <em>stereo<\/em> FM radio<\/h3>\n<ul>\n<li><strong>Frequency:<\/strong> 87.5-108 MHz<\/li>\n<li><strong>Modulation:<\/strong> FM<\/li>\n<\/ul>\n<p>How stereo audio is transmitted is really interesting, because it\u2019s backwards-compatible to receivers that don\u2019t support it:<\/p>\n<p>Here, you see the demodulated audio frequency spectrum, as shown in SDRangel. Below 19k Hz, it\u2019s just mono audio. Then, to mark a stereo station, there\u2019s a constant \u201cpilot tone\u201d at 19k Hz! (Outside of what most humans can hear.)<\/p>\n<p>Then, if you double the frequency of the pilot tone, you can derive the sections where the difference of the left &#038; right channel to the mono channel is transmitted!<\/p>\n<p><strong>Correction:<\/strong> I\u2019ve been told that instead of what I call \u201cleft\u201d and \u201cright\u201d in this diagram, the upper frequencies transmit the <em>difference of the left and right channels<\/em>! That way, the receiver can calculate the left and right channels from the mono signal (which is, esseutially, the <em>sum<\/em> of left and right).<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/117da03f9f7ff03c.png\" alt=\"software An audio spectrum, with the pilot tone and the frequency ranges marked in blue.\" title=\"software An audio spectrum, with the pilot tone and the frequency ranges marked in blue.\"><\/p>\n<h3 id=\"receive-road-traffic-information\">7: Receive road traffic information<\/h3>\n<ul>\n<li><strong>Frequency:<\/strong> 87.5-108 MHz<\/li>\n<\/ul>\n<p>If you <em>triple<\/em> 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\u2019s a protocol called Radio Data System.<\/p>\n<p>This system can also transmit road traffic information! There seemed to be a road closure at \u201c0x64BE\u201d, as decoded by SDRangel.<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/1d19e5388d95bcab.png\" alt=\"software Metadata of a station called N-JOY.\" title=\"software Metadata of a station called N-JOY.\"><\/p>\n<p>The Federal Highway Research Institute publishes an Excel table, where I could look up that this is a town in Lower Saxony!<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/dc403604e704fc79.png\" alt=\"software An Excel file, with the proper street and town highlighted.\" title=\"software An Excel file, with the proper street and town highlighted.\"><\/p>\n<h3 id=\"listen-to-conversations-on-the-2-meter-amateur-radio-band\">8: Listen to conversations on the 2-meter amateur radio band<\/h3>\n<ul>\n<li><strong>Frequency:<\/strong> 144-146 MHz<\/li>\n<li><strong>Modulation:<\/strong> FM<\/li>\n<\/ul>\n<p>This is a frequency range reserved for amateur radio operators \u2013 for non-commercial use only. You may send on this band after getting a license.<\/p>\n<p>What I found here is seemingly a conversation circle facilitated by a relay around 15 km away from here \u2013 it takes input on a certain frequency, and outputs an amplified copy of it on another frequency! Klaus, Bernd, J\u00fcrgen and Horst were talking about antennas, relays, and Windows XP! \ud83d\ude01<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/ba8aecf90d72d5b2.png\" alt=\"software An FM signal at 145.75 MHz.\" title=\"software An FM signal at 145.75 MHz.\"><\/p>\n<h3 id=\"listen-to-digital-radio\">9: Listen to digital radio<\/h3>\n<ul>\n<li><strong>Frequency:<\/strong> 174-240 MHz<\/li>\n<\/ul>\n<p>The SDRangel software also has a demodulator for Digital Audio Broadcast! :O I continue to be amazed by it!<\/p>\n<p>I think this was the first time I\u2019ve received digital radio via air! I saw so many stations, and I\u2019ve only checked a couple of channels.<\/p>\n<p>The advantage of this digital channel is that there\u2019s no noise. And I even saw a \u201ccover image\u201d in one of the programs!<\/p>\n<p><video src=\"http:\/\/blinry.org\/57ee52cbbbfe70d1.mp4\" controls><\/video><\/p>\n<h3 id=\"listen-to-pmr446\">10: Listen to PMR446<\/h3>\n<ul>\n<li><strong>Frequency:<\/strong> 446.0-446.2 MHz<\/li>\n<li><strong>Modulation:<\/strong> FM<\/li>\n<\/ul>\n<p>This is a frequency range for \u201cPrivate Mobile Radio\u201d. It\u2019s another of these bands where anyone can transmit using a licensed device!<\/p>\n<p>Not a lot of activity here. I heard \u201cHello, hellooo!\u201d, \u201cCan you hear me?\u201d and some short transmissions that sounded like a child! \ud83d\ude00<\/p>\n<p>There also seemed to be digital transmissions, but I didn\u2019t know how to decode them yet.<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/9138cbe316231071.png\" alt=\"software Some speech burts in a noisy waterfall diagram.\" title=\"software Some speech burts in a noisy waterfall diagram.\"><\/p>\n<p>The range of PMR446 devices is pretty low (a couple of hundred metres in cities), so again, the people must\u2019ve been close!<\/p>\n<h2 id=\"tuesday\">Tuesday<\/h2>\n<p>After the first day of SDR experiments, I was amazed how much invisible communication is going on around us in the electromagnetic spectrum at the same time!<\/p>\n<p>I posted each of these things on Mastodon as I went, and asked people for suggestions for more things I could receive.<\/p>\n<h3 id=\"read-your-neighbors-sensors\">11: Read your neighbors\u2019 sensors<\/h3>\n<ul>\n<li><strong>Frequency:<\/strong> 433.05-434.79 MHz<\/li>\n<\/ul>\n<p>At 433 MHz, there\u2019s a frequency band for \u201cindustrial, scientific and medical\u201d applications. And wow, there was quite a lot of activity nearby!<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/00f1744c6d7d5180.png\" alt=\"software Short signal bursts in the frequency spectrum, at different frequencies around 433 MHz.\" title=\"software Short signal bursts in the frequency spectrum, at different frequencies around 433 MHz.\"><\/p>\n<p>Using the decoder rtl_433, I saw two sensors that output the current temperature, humidity, and air pressure!<\/p>\n<p>There were also some \u201cIBIS beacons\u201d flying by, which are used in public transportation, so maybe it\u2019s buses driving by?<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/88f09ea499f9273d.png\" alt=\"software Command line output of rtl_433, reporting sensor data.\" title=\"software Command line output of rtl_433, reporting sensor data.\"><\/p>\n<p>Later, an \u201cInterlogix Security\u201d device also appeared, reporting \u201cclosed switch states\u201d :O<\/p>\n<h3 id=\"track-ships\">12: Track ships!<\/h3>\n<ul>\n<li><strong>Frequency:<\/strong> 162.025 MHz<\/li>\n<\/ul>\n<p>Ships send out their status using AIS (Automatic Identification System). And again, I received <em>a lot<\/em> of them here in Hamburg! :O<\/p>\n<p>I was especially excited to receive data from the MS Stubnitz (a fisher boat that was turned into a culture center\/techno club)! It reports its status as \u201cmoored\u201d, and its speed as 0.1 knots! \ud83d\ude00<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/f99730ce760ad7f9.png\" alt=\"software A table of ships, along with a map.\" title=\"software A table of ships, along with a map.\"><\/p>\n<p>Again, I used the software SDRangel. Apparently, it can also display a 3D map, but I haven\u2019t figured out how to add 3D models\u2026<\/p>\n<h3 id=\"detect-gsm-activity\">13: Detect GSM activity<\/h3>\n<ul>\n<li><strong>Frequency:<\/strong> 876-959 MHz, I looked up the specific ranges for Germany on Wikipedia<\/li>\n<\/ul>\n<p>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.<\/p>\n<p>What surprised me most: You can kind of \u201csee\u201d the volume at which I was talking!?<\/p>\n<p>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 \u201creceiving\u201d direction.<\/p>\n<p><video src=\"http:\/\/blinry.org\/9ef1c5c2fec6053d.mp4\" controls><\/video><\/p>\n<h2 id=\"wednesday\">Wednesday<\/h2>\n<h3 id=\"receive-signals-from-a-satellite\">14: Receive signals from a satellite!<\/h3>\n<ul>\n<li><strong>Frequency:<\/strong> 136-138 MHz<\/li>\n<\/ul>\n<p>I spent all Tuesday afternoon and evening learning about satellites. The program gpredict is really nice to find out when satellites will pass overhead! I learned a lot, including that one satellite I was trying to receive burned up last week! \ud83d\ude00<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/4193c146fe11aac1.png\" alt=\"software A map of the Earth, with satellite positions and predictions.\" title=\"software A map of the Earth, with satellite positions and predictions.\"><\/p>\n<p>I was super excited when I first received a signal from a NOAA satellite! \ud83d\udef0\ufe0f<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/0d64ef01beb64d32.png\" alt=\"software A striped signal in a waterfall diagram, at around 137 MHz.\" title=\"software A striped signal in a waterfall diagram, at around 137 MHz.\"><\/p>\n<p>But I didn\u2019t manage to decode it properly yet. Maybe my reception was too noisy? I wanted to keep trying, but I had to move on.<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/64de2491fb3d1ae5.png\" alt=\"software A noisy image with borders.\" title=\"software A noisy image with borders.\"><\/p>\n<h3 id=\"admire-tetra-signals\">15: Admire TETRA signals<\/h3>\n<p>In Germany, the police has switched to an encrypted digital protocol called TETRA.<\/p>\n<p>Even though I\u2019ve seen some interesting talks at CCC events about weaknesses in the decryption, all I wanted to do for now is looking at the pretty signals in SDR++. :3<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/dca4c590f7d2da84.png\" alt=\"software Colorful, very orderly strips in a waterfall diagram.\" title=\"software Colorful, very orderly strips in a waterfall diagram.\"><\/p>\n<h3 id=\"listen-to-taxi-dispatchers\">16: Listen to taxi dispatchers<\/h3>\n<p>Again, this is communication not meant for the general public.<\/p>\n<p>I didn\u2019t listen to someone dispatching taxis to specific addresses, and you also shouldn\u2019t do that either. \ud83d\ude95<\/p>\n<p>Stay away from a site called \u201cfrequenzdatenbank\u201d!<\/p>\n<h3 id=\"ponder-mysterious-signals\">17: Ponder mysterious signals<\/h3>\n<p>Some of the most fun I had was just browsing frequencies and seeing what I can find! Sometimes, I encountered signals I can\u2019t identify.<\/p>\n<p>For example, at 865-868 MHz, there was a family of slow, continuous, digital signals that made a nice melody when listened to in single-sideband demodulation!<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/d1f3086c9e6f0e4a.png\" alt=\"software Digital chirps, separated by 200 kHz.\" title=\"software Digital chirps, separated by 200 kHz.\"><\/p>\n<p>And at 177-180 MHz, there were two very broadband transmissions. Might be TV? But I couldn\u2019t find out what type. (It later turned out that I\u2019d already listened to these signals \u2013 it was digital radio, DAB+.)<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/ccf19960970b8fe5.png\" alt=\"software Broadband RF in a waterfall diagram.\" title=\"software Broadband RF in a waterfall diagram.\"><\/p>\n<h3 id=\"track-weather-balloons\">18: Track weather balloons<\/h3>\n<ul>\n<li><strong>Frequency:<\/strong> 400-405.9 MHz<\/li>\n<\/ul>\n<p>As I was browsing around for things to receive, I saw on this tracking website that a radiosonde was just launched in Hamburg! SDRangel could decode its transmission! It had climbed to a height of 7 km, and it\u2019s -17 \u00b0C there!<\/p>\n<p>I knew that it would eventually burst and fall back to Earth, and that I could try to get to it and find it!<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/158b4820a354d902.png\" alt=\"software Data about the balloon. Location on a map, height data graph.\" title=\"software Data about the balloon. Location on a map, height data graph.\"><\/p>\n<h3 id=\"hunt-weather-balloons\">19: <em>Hunt<\/em> weather balloons!<\/h3>\n<p>I decided to go on a field trip, using trains and my bike.<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/9f2f23bd87802298.jpg\" alt=\"software I'm holding a bike at a train station.\" title=\"software I'm holding a bike at a train station.\"><\/p>\n<p>I was following the tracker. The balloon popped earlier than predicted, and I frantically changed travel plans!<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/4722c8707fad48c0.jpeg\" alt=\"software Balloon paths on map.\" title=\"software Balloon paths on map.\"><\/p>\n<p>Eventually, it landed in a forest. I hoped I could get to it! What made this adventure more tricky was that my mobile Internet contract ran out while I was on the go, and my battery was also almost empty.<\/p>\n<p>But I made it to the forest, and entered it.<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/4a198ccef135bdf3.jpg\" alt=\"software All pictures show me in a swampy forest.\" title=\"software All pictures show me in a swampy forest.\"><\/p>\n<p>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.<\/p>\n<p>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.<\/p>\n<p>He told me that he had found around 40 of them so far!<\/p>\n<p>Usually, the sondes keep broadcasting after landing, but this one wasn\u2019t. So he quickly guessed that someone else could\u2019ve taken it. Or maybe it landed in the water and died?<\/p>\n<p>Some pictures of the area we searched:<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/90f66724915ebe41.jpg\" alt><\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/aba76e16c50cafac.jpg\" alt><\/p>\n<p>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!<\/p>\n<p>And he was right: Someone had been faster than us! The status was changed. So in the end, I didn\u2019t find the sonde. But something that might be even better \u2013 a friend!<\/p>\n<h3 id=\"receive-amateur-packet-radio\">20: Receive amateur packet radio<\/h3>\n<ul>\n<li><strong>Frequency:<\/strong> 144.8 MHz<\/li>\n<\/ul>\n<p>In the 2-meter amateur band, there are certain frequencies for the \u201cAutomatic Packet Reporting System\u201d. It\u2019s a bit like IP \u2013 packets have a \u201cfrom\u201d and a \u201cto\u201d. They can also broadcast their position, or weather data.<\/p>\n<p>Some stations seem to announce themselves as repeaters, which probably help forward the packets to increase the range.<\/p>\n<p>And two people seemed to be on a \u201cfieldday\u201d, and broadcasted their location. \ud83d\ude00<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/8574d165534474e5.png\" alt=\"software A table of packets in a rather cryptic format.\" title=\"software A table of packets in a rather cryptic format.\"><\/p>\n<p>SDRangel can create a map automatically:<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/8a8b76e532277035.png\" alt=\"software Icons on a map around Hamburg.\" title=\"software Icons on a map around Hamburg.\"><\/p>\n<h2 id=\"thursday\">Thursday<\/h2>\n<p>I started the day by building an antenna!<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/fe8dbe63472e66d9.jpg\" alt=\"software A big roll of green wire.\" title=\"software A big roll of green wire.\"><\/p>\n<p>This was going to be a simple \u201crandom wire\u201d antenna, to allow me to get better reception in the lower frequencies, which I\u2019ve omitted so far (because I knew it would be much more fun with a better antenna)!<\/p>\n<p>I measured out 21.6 m of wire (which for \u2728magic\u2728 reasons seem to be a good universal antenna length)\u2026<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/73e5201fdfad8421.png\" alt=\"software Green wire spread across a carpet.\" title=\"software Green wire spread across a carpet.\"><\/p>\n<p>\u2026directly attached it to the center of another SMA connector\u2026<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/12235733fb4034fa.jpg\" alt=\"software A golden screwable connector on the end of the wire.\" title=\"software A golden screwable connector on the end of the wire.\"><\/p>\n<p>\u2026and draped it all around my room!<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/a623475543e9868f.png\" alt=\"software The green wire draped over a wooden shelf.\" title=\"software The green wire draped over a wooden shelf.\"><\/p>\n<p>People on the Internet say that there are many problems with this \u2013 that it would be better to have it outside, and that there\u2019s an impedance mismatch between the receiver and the wire.<\/p>\n<p>I could address those problems, but I wanna try how well this works first \ud83d\ude42<\/p>\n<h3 id=\"receive-morse-code-from-other-countries\">21: Receive Morse code from other countries<\/h3>\n<ul>\n<li><strong>Frequency:<\/strong> 10.10-10.13 MHz<\/li>\n<li><strong>Modulation:<\/strong> CW (\u201ccontinuous wave\u201d)<\/li>\n<\/ul>\n<p>On the 30-meter amateur band, I found people sending Morse code! :O<\/p>\n<p>I\u2019d been learning it a little bit, so if I recorded it and slowed it down, I could understand it: They\u2019re sending their callsigns. These are from Belgium, France, and Italy! o\/<\/p>\n<p><video src=\"http:\/\/blinry.org\/41b56fe1ef140bd5.mp4\" controls><\/video><\/p>\n<p>I compared to my 2-meter dipole antenna, and the reception was definitely better \u2013 I can pick up more transmissions, and with much less noise!<\/p>\n<h3 id=\"receive-maritime-weather-reports\">22: Receive maritime weather reports<\/h3>\n<ul>\n<li><strong>Frequency:<\/strong> 11.039 MHz<\/li>\n<\/ul>\n<p>The German Weather Service broadcasts maritime information throughout the day on various shortwave frequencies.<\/p>\n<p>They use a protocol called RTTY (radioteletype), and it took me a while to decode it. But I found a neat little program called \u201cfldigi\u201d: You can pipe audio to it (single side band modulation), and then if you pick the correct settings (see screenshot), it happily transcribes the messages!<\/p>\n<p>Here\u2019s the station weather reports for the Baltic Sea and Northern Sea!<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/4fd45254eab3176f.png\" alt=\"software The reports contain temperature, pressure, and wind direction.\" title=\"software The reports contain temperature, pressure, and wind direction.\"><\/p>\n<h3 id=\"receive-digimodes-from-other-countries\">23: Receive digimodes from other countries<\/h3>\n<ul>\n<li><strong>Frequency:<\/strong> 10.130-10.15 MHz<\/li>\n<\/ul>\n<p>I found some other strange signals on the 30-meter band. The Signal Identification Wiki was really helpful for figuring out what they were: FT8!<\/p>\n<p>FT8 is quite 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).<\/p>\n<p>This is the WSJT-X software.<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/9d65a50a712d4873.png\" alt=\"software A waterfall diagram, and a table of decoded messages.\" title=\"software A waterfall diagram, and a table of decoded messages.\"><\/p>\n<h3 id=\"detect-whether-your-notebook-is-charging\">24: Detect whether your notebook is charging<\/h3>\n<ul>\n<li><strong>Frequency:<\/strong> Below 1 MHz<\/li>\n<\/ul>\n<p>As I was browsing the very low-frequency bands, I had a strange problem: Sometimes, that would work okayish, sometimes I could even make out voices!<\/p>\n<p>But other times, it wouldn\u2019t work at all, and everything would be loud, angry noise. Even in regions where I had better reception before!<\/p>\n<p>Eventually, I found out how to solve that issue \u2013 by unplugging my notebook charger. D\u2019oh! \ud83d\ude00<\/p>\n<p><video src=\"http:\/\/blinry.org\/068d1287e06581c8.mp4\" controls><\/video><\/p>\n<h3 id=\"see-ionosondes-and-radar-signals\">25 &#038; 26: See ionosondes and radar signals<\/h3>\n<ul>\n<li><strong>Frequency:<\/strong> 6-30 MHz<\/li>\n<\/ul>\n<p>In the low frequencies, occasionally, you can hear a short <em>chirp<\/em>! \ud83d\ude00 These are caused by ionosondes, scientific instruments which measure the properties of the ionosphere by sweeping a wide frequency spectrum.<\/p>\n<p>Another signal (which I accidentally got in the same screenshot) is a radar system \u2013 in this case, according to the Signal Identification Wiki, it\u2019s a \u201cCODAR\u201d system, used to measure the motion of water waves and currents along coasts! :O<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/9c312ae5e3f42bfa.png\" alt=\"software A diagonal line across 16 MHz, and a shorter, repeating pattern, repeating 4 times a second.\" title=\"software A diagonal line across 16 MHz, and a shorter, repeating pattern, repeating 4 times a second.\"><\/p>\n<h3 id=\"listen-to-single-side-band-conversations\">27: Listen to \u201csingle side band\u201d conversations<\/h3>\n<ul>\n<li><strong>Frequency:<\/strong> In all amateur bands, especially the ones below 30 MHz<\/li>\n<li><strong>Modulation:<\/strong> SSB (\u201csingle side band\u201d)<\/li>\n<\/ul>\n<p>How do you transmit speech over long distances? You can use \u201camplitude modulation\u201d, where you change the volume of the carrier frequency to model your audio.<\/p>\n<p>As a side effect, the bands to the sides of the carrier will contain a signal, as well.<\/p>\n<p>One trick is to transmit <em>just<\/em> those sidebands, which saves power! But you have to \u201cguess\u201d the base frequency when listening. Depending on which part you transmit, this is called \u201clower side band\u201d or \u201cupper side band\u201d.<\/p>\n<p>SDR++ makes it very easy to play with this! \ud83d\ude42 Here\u2019s someone from Serbia!<\/p>\n<p><video src=\"http:\/\/blinry.org\/2afcbe7fd3bb5662.mp4\" controls><\/video><\/p>\n<h3 id=\"listen-to-am-radio-from-the-other-side-of-the-world\">28: Listen to AM radio from the other side of the world<\/h3>\n<ul>\n<li><strong>Frequency:<\/strong> Shortwave bands below 26 MHz<\/li>\n<\/ul>\n<p>At night, low-frequency radio waves can travel further around the world, because they\u2019re reflected by the layers of the ionosphere! There\u2019s something magical about this.<\/p>\n<p>I put my antenna outside, and I could hear <em>a lot<\/em> of broadcasting stations! On short-wave.info, you can look up where they are located.<\/p>\n<p>Some stations in China are broadcasting with very high power! Some I could hear were over 7500 km away.<\/p>\n<p>Wow. It\u2019s full of stars! \ud83c\udf0c<\/p>\n<p><video src=\"http:\/\/blinry.org\/64de3ddfeb284a58.mp4\" controls><\/video><\/p>\n<h2 id=\"friday\">Friday<\/h2>\n<p>Originally, I had planned the project to run from Monday to Friday. When I still had 32 things to do in Friday morning, I knew I\u2019d need to extend it. But I hadn\u2019t run out of ideas yet:<\/p>\n<h3 id=\"listen-to-cb-radio\">29: Listen to CB radio<\/h3>\n<ul>\n<li><strong>Frequency:<\/strong> 26.965-27.405 MHz<\/li>\n<li><strong>Modulation:<\/strong> FM or AM<\/li>\n<\/ul>\n<p>After I\u2019d looked into the low frequencies on Thursday, I went to a higher band again: The Citizens Band!<\/p>\n<p>This is the third frequency band I\u2019m aware of where anyone is allowed to transmit \u2013 provided that you use a licensed device!<\/p>\n<p>This is a band where my random wire antenna really came in handy. Without it, I would have had a hard time understanding anything. And even with it, transmissions are extremely noisy.<\/p>\n<p>CB radio is used internationally, especially by truck drivers, it seems.<\/p>\n<p><video src=\"http:\/\/blinry.org\/2f373dda05a9737e.mp4\" controls><\/video><\/p>\n<h3 id=\"assess-the-propagation-of-radio-waves-using-beacons\">30: Assess the propagation of radio waves using beacons<\/h3>\n<ul>\n<li><strong>Frequency:<\/strong> 14.100, 18.110, 21.150, 24.930, and 28.200 MHz<\/li>\n<li><strong>Modulation:<\/strong> CW<\/li>\n<\/ul>\n<p>The International Beacon Project runs a network of 18 stations, which take turns transmitting their callsigns at certain frequencies.<\/p>\n<p>Using this system, you can quickly get a sense of how well radio waves are currently propagating to your location. Clever!<\/p>\n<p>I picked up the beacon from southern Finland! You can see its callsign scrolling away in the video. It\u2019s followed by four dashes send with decreasing power. I only heard the first one\u2026<\/p>\n<p><video src=\"http:\/\/blinry.org\/4909ef87ba8bc182.mp4\" controls><\/video><\/p>\n<h3 id=\"receive-a-time-signal\">31: Receive a time signal<\/h3>\n<ul>\n<li><strong>Frequency:<\/strong> 9996 kHz<\/li>\n<li><strong>Modulation:<\/strong> CW<\/li>\n<\/ul>\n<p>I would\u2019ve 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\u2019t think my dongle can do that.<\/p>\n<p>So I used higher frequencies! Russia transmits its \u201cRWM\u201d time signal at 9996 kHz, which beeps every second, with a long beep for the full minute.<\/p>\n<p>Not enough to tell the time, but enough to adjust your wrist watch, I guess!<\/p>\n<p><video src=\"http:\/\/blinry.org\/2bc9c809876b536b.mp4\" controls><\/video><\/p>\n<h3 id=\"receive-a-weather-fax\">32: Receive a weather fax<\/h3>\n<ul>\n<li><strong>Frequency:<\/strong> 3855, 7880, and 13882.5 kHz (see weatherfax.com for more)<\/li>\n<\/ul>\n<p>The German Weather Service broadcasts weather maps throughout the day! You can decode them using fldigi\u2019s \u201cWEFAX-576\u201d setting.<\/p>\n<p>I caught this one only halfway through. According to the schedule, it\u2019s the \u201cSurface weather chart North Atlantic, Europe\u201d!<\/p>\n<p>If you squint <em>really<\/em> hard, you can make out the coast of Spain and the Mediterranean Sea on the right side!<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/3e5447217ad0d450.png\" alt=\"software A partial map with pressure lines on it. Number's are hard to read. At the bottom, there's today's date, and a copyright note by the Deutscher Wetterdienst.\" title=\"software A partial map with pressure lines on it. Number's are hard to read. At the bottom, there's today's date, and a copyright note by the Deutscher Wetterdienst.\"><\/p>\n<h3 id=\"decode-images-from-a-weather-satellite\">33: Decode images from a weather satellite!<\/h3>\n<ul>\n<li><strong>Frequency:<\/strong> 137.62, 137.9125, and 137.1 MHz<\/li>\n<\/ul>\n<p>I couldn\u2019t stop trying to capture a weather satellite, it\u2019s just too cool to receive an image from space!<\/p>\n<p>That evening, an American satellite called NOAA-15 passed right over us, so I thought I\u2019d try again. And this time, I got parts of an image! o\/<\/p>\n<p>This is real-time data! At night, both transmitted images are infrared recordings.<\/p>\n<p>I recorded the FM signal using SDR++, and then decoded the image using noaa-apt, which also added country outlines.<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/f03b58a0472b0d32.png\" alt=\"software Grayscale map of Europe, with several very noisy parts. Border lines are drawn on top. You can see a cloud cover on Italy.\" title=\"software Grayscale map of Europe, with several very noisy parts. Border lines are drawn on top. You can see a cloud cover on Italy.\"><\/p>\n<h3 id=\"estimate-the-speed-of-satellites\">34: Estimate the speed of satellites<\/h3>\n<ul>\n<li><strong>Frequency:<\/strong> 136-138 MHz<\/li>\n<\/ul>\n<p>Here\u2019s what the NOAA-15 weather satellite sounds like, by the way! <em>tick-tock<\/em><\/p>\n<p>While recording, I noticed something strange: The transmission didn\u2019t happen at the frequency I had expected it to! And also, the frequency changed.<\/p>\n<p>Then it hit me: Doppler effect! At the time of the recording, the frequency was around 4250 Hz higher than expected.<\/p>\n<p>After looking up the formula, I calculated a relative speed of 9 km\/s! (Which got close to its real speed, 7.5 km\/s.)<\/p>\n<p><video src=\"http:\/\/blinry.org\/59b7a4e629869e09.mp4\" controls><\/video><\/p>\n<h3 id=\"listen-to-number-stations\">35: Listen to number stations<\/h3>\n<ul>\n<li><strong>Frequency:<\/strong> 5-30 MHz?<\/li>\n<li><strong>Modulation:<\/strong> Differs by station<\/li>\n<\/ul>\n<p>These stations send encrypted messages using number sequences, possibly for espionage purposes!<\/p>\n<p>So why not listen to one? There\u2019s a surprisingly well-maintained database of them on a site call Priyom.<\/p>\n<p>So I tuned into the next frequency that was listed, and: Bingo!<\/p>\n<p>Allegedly, this was a station in Moscow. That day, it sent \u201c218, 218, 218\u201d in a loop, followed by three long beeps, which is the format of a \u201cnull message\u201d.<\/p>\n<p>So no news for the Russian spies.<\/p>\n<p><video src=\"http:\/\/blinry.org\/060921524b7db346.mp4\" controls><\/video><\/p>\n<h2 id=\"saturday\">Saturday<\/h2>\n<p>The week was really intense for me. Initially, I thought I\u2019d do 10 things per day, but it turned out that that was too much. I had to learn so many new things.<\/p>\n<p>Many things I tried don\u2019t work on my first attempt. Finding LoRaWAN signals, decoding packet radio, finding something on PMR446, decoding the satellite \u2013 those were all things that required a second (or third) attempt.<\/p>\n<p>This project was exhausting, but also joyful \u2013 having committed to it, I got in a nice flow state, where I could focus on it for hours.<\/p>\n<p>Often, I thought: \u201cOkay, this is it. I can\u2019t possibly find more things.\u201d 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\u2019t have tried!<\/p>\n<p>So, 15 more things, huh?<\/p>\n<h3 id=\"receive-images-from-amateur-radio-operators\">36: Receive images from amateur radio operators<\/h3>\n<ul>\n<li><strong>Frequency:<\/strong> 14.230, 14.233, 21.340, 28.680, 145.625 MHz seem to be popular<\/li>\n<\/ul>\n<p>Using a protocol called \u201cSSTV\u201d (slow-scan television), amateur radio operators send each other postcards! \ud83d\ude00<\/p>\n<p>I\u2019ve been browsing the usual frequencies, and tried to decode images using the software QSSTV on Linux. And I accidentally caught a piece of what seems to be a test image!<\/p>\n<p>SSTV has the prettiest noise! :3<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/dcd37ab4912cae59.png\" alt=\"software Colorful TV test image at the top, colorful noise at the bottom.\" title=\"software Colorful TV test image at the top, colorful noise at the bottom.\"><\/p>\n<h3 id=\"listen-to-the-buzzer\">37: Listen to The Buzzer<\/h3>\n<ul>\n<li><strong>Frequency:<\/strong> 4625 kHz<\/li>\n<li><strong>Modulation:<\/strong> Upper side band<\/li>\n<\/ul>\n<p>There\u2019s a mysterious Russian station broadcasting at 4625 kHz. Sometimes, it sends encrypted voice messages.<\/p>\n<p>But usually, all it does is send a honking sound every two seconds, to deter other stations from using the same frequency.<\/p>\n<p>The purpose of the station is unclear, but most theories think it\u2019s military communication.<\/p>\n<p><video src=\"http:\/\/blinry.org\/a66449021d13a72c.mp4\" controls><\/video><\/p>\n<h3 id=\"catch-a-lorawan-chirp\">38: Catch a LoRaWAN chirp<\/h3>\n<ul>\n<li><strong>Frequency:<\/strong> 868.1-868.5 MHz<\/li>\n<\/ul>\n<p>This was a bit like trying to catch a rare insect! \ud83d\udc1b<\/p>\n<p>LoRaWAN is a low-power, wide-area networking protocol, intended for \u201cInternet of Things\u201d applications.<\/p>\n<p>You can see transmission in the lower half of the screenshot! It has a very cute structure: You can see eight \u201cdown-chirps\u201d, followed by two \u201cup-chirps\u201d. That\u2019s the header, followed by the payload.<\/p>\n<p>To look for the signal, I made a \u201cbaseband capture\u201d in SDR++, and opened the recording in Sonic Visualizer.<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/be27f9c605c4eaad.png\" alt=\"software A spectrogram, displaying a signal consisting of diagonal lines.\" title=\"software A spectrogram, displaying a signal consisting of diagonal lines.\"><\/p>\n<h3 id=\"read-data-from-utility-meters\">39: Read data from utility meters<\/h3>\n<ul>\n<li><strong>Frequency:<\/strong> 868.95 MHz<\/li>\n<\/ul>\n<p>Devices like smoke detectors or meters for water or heat are sending their readings via a protocol called Wireless M-Bus.<\/p>\n<p>Again, I was surprised by how many devices seem to be around! Thanks for the tip, @envy \ud83d\ude42<\/p>\n<p>wmbusmeters is a really nice tool for decoding the messages.<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/2732b0f9fb5a28b7.png\" alt=\"software A log of transmissions found, and a decoded message that gives room and radiator temperature.\" title=\"software A log of transmissions found, and a decoded message that gives room and radiator temperature.\"><\/p>\n<h3 id=\"watch-tv\">40: \u201cWatch\u201d TV<\/h3>\n<ul>\n<li><strong>Frequency:<\/strong> 174-786 MHz<\/li>\n<\/ul>\n<p>The chips in my SDR stick are also being used in DVB-T dongles! So, can we watch TV? Unfortunately, no.<\/p>\n<p>From what I pieced together, there\u2019s 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).<\/p>\n<p>In Germany, there\u2019s now DVB-T2, which my hardware doesn\u2019t 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<\/p>\n<p><video src=\"http:\/\/blinry.org\/298b8a7c6a56cd04.mp4\" controls><\/video><\/p>\n<h3 id=\"track-cars-and-buses\">41: Track cars and buses<\/h3>\n<ul>\n<li><strong>Frequency:<\/strong> 433.05-434.79 MHz<\/li>\n<\/ul>\n<p>Did a little walk to a big intersection, to see what \u201cdevice signals\u201d I\u2019d find there at 433 MHz.<\/p>\n<p>I could confirm that the IBIS beacons are in fact being sent by buses! The included \u201cvehicle ID\u201d even matches the white number that\u2019s printed on it.<\/p>\n<p>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\u2019t aware how easy it would be to track them\u2026 (Thanks, @scy!)<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/24514cc9f989de85.jpeg\" alt=\"software A bus on an intersection. There's a white number printed on it at the front.\" title=\"software A bus on an intersection. There's a white number printed on it at the front.\"><\/p>\n<p>Side note: I wonder why some signals in that band are warped like the one at 433.96 MHz here!<\/p>\n<p>At first, I thought \u201cAh, Doppler effect again, it\u2019s coming from a moving car!\u201d But if that\u2019d be the case, that car would be moving at over 700 m\/s\u2026<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/24108965ac1d0455.png\" alt=\"software One signal has a little frequency warp to it.\" title=\"software One signal has a little frequency warp to it.\"><\/p>\n<p>Friends later suspected that this effect is due to weak batteries affecting the crystal in the sending devices, or temperature changes.<\/p>\n<h3 id=\"receive-morse-code-from-a-satellite\">42: Receive Morse code from a satellite!<\/h3>\n<ul>\n<li><strong>Frequency:<\/strong> 145.860 (status information) and 145.960 (beacon)<\/li>\n<li><strong>Modulation:<\/strong> CW<\/li>\n<\/ul>\n<p>So I caught a satellite again! \ud83d\ude00 This time, it was school project, the Italian satellite \u201cMax Valier\u201d. It continuously sends Morse code on a beacon frequency.<\/p>\n<p>Pretty weak signal, but here\u2019s what I could hear:<\/p>\n<p><code><br \/>\n3MV MAX VALIER SAT ... MANFRED ES CHRISTA FUKSE 73 ... II3MV ...<br \/>\n<\/code><\/p>\n<p>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? I later learned that <code>ES<\/code> is Morse code shorthand for \u201cand\u201d, and that Manfred and Christa Fuchs were the founders of a company that helped launch the satellite!<\/p>\n<p>(Thanks for the tip, @manawyrm!)<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/9c049d30d265cbb9.png\" alt=\"software Faint Morse code in a waterfall diagram.\" title=\"software Faint Morse code in a waterfall diagram.\"><\/p>\n<p>This is another thing that\u2019s not allowed in Germany, so you shouldn\u2019t do it.<\/p>\n<p>Pagers use a format called \u201cPOCSAG\u201d (Post Office Code Standardisation Advisory Group\u2026), which you should not decode using multimon-ng.<\/p>\n<p>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.<\/p>\n<p>Do not read the English Wikipedia page! It contains frequencies!<\/p>\n<h2 id=\"sunday\">Sunday<\/h2>\n<p>At this point, I was pretty tired. Focusing on this project for 6 days straight took a lot of energy, and I was always uncertain if I could actually complete all 50 things in that week! But I woke up with a fun idea:<\/p>\n<h3 id=\"detect-when-a-smartphone-is-turned-on\">44: Detect when a smartphone is turned on<\/h3>\n<ul>\n<li><strong>Frequency:<\/strong> 13.56 MHz<\/li>\n<\/ul>\n<p>I was curious whether I could see the NFC transceiver in my smartphone! And yeah, especially using my random wire antenna, this works really well!<\/p>\n<p>My smartphone seems to emit at the NFC frequency a couple of times per second. And when unlocking the screen, it emits five very strong beeps on that frequency! I can see those from the other side of our apartment.<\/p>\n<p>Surely, these signals are the same for every device, right? \ud83d\ude36<\/p>\n<p>Observe the five beeps here:<\/p>\n<p><video src=\"http:\/\/blinry.org\/feb0a619986a7006.mp4\" controls><\/video><\/p>\n<h3 id=\"communicate-wirelessly-using-a-book\">45: Communicate wirelessly using\u2026 a book<\/h3>\n<ul>\n<li><strong>Frequency:<\/strong> 13.56 MHz<\/li>\n<\/ul>\n<p>Piko and I played around with NFC a bit more, and we found out that when getting close to an NFC tag, a smartphone emits at 13.56 MHz continuously!<\/p>\n<p>So, we started sending Morse code to each other between rooms, using a smartphone and a library book! :\u2019D<\/p>\n<p>Take that, Bundesnetzagentur!<\/p>\n<p>Seems that the shortest signal you can create is 0.7 s long, resulting in a meager communication speed of 3-4 words per minute\u2026<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/4c63b62ed100e688.png\" alt=\"software Morse code signs in a waterfall diagram.\" title=\"software Morse code signs in a waterfall diagram.\"><\/p>\n<h3 id=\"receive-navigational-aids-for-airplanes\">46: Receive navigational aids for airplanes<\/h3>\n<ul>\n<li><strong>Frequency:<\/strong> 108.00-117.95 MHz<\/li>\n<\/ul>\n<p>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. (Thanks, @fly_it!)<\/p>\n<p>I heard the one close to Hamburg! And SDRangel has a decoder, of course! It calculated angles between 210\u00b0 and 230\u00b0, which is pretty close to the actual value of 224\u00b0! I don\u2019t think they are meant to be used from the ground.<\/p>\n<p>The neat navigational map is from https:\/\/skyvector.com!<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/5029b31e8a681a21.png\" alt=\"software View of SDRangel, it decodes the signal in the lower left, and shows 229\u00b0!\" title=\"software View of SDRangel, it decodes the signal in the lower left, and shows 229\u00b0!\"><\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/273232dae2961991.png\" alt=\"software An aeronautic navigational chart.\" title=\"software An aeronautic navigational chart.\"><\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/408727dc40cc80cc.png\" alt=\"software A map where I show that the real angle is 224 degrees.\" title=\"software A map where I show that the real angle is 224 degrees.\"><\/p>\n<p>I spent ages trying to build my own decoder in GNU Radio. But I wasn\u2019t familiar with it at all, and I eventually gave up. Still, that seems to be the software you wanna learn for tasks like these!<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/0e55a27def0a797d.png\" alt=\"software All screenshots show experiments I did in GNU Radio and Audacity.\" title=\"software All screenshots show experiments I did in GNU Radio and Audacity.\"><\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/95edb38ca810d73b.png\" alt><\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/2be773fb7f56d5d7.png\" alt><\/p>\n<p>By the way, how the ground stations work is fascinating: In my case, it\u2019s a \u201cDoppler VOR\u201d: It transmits a static frequency via amplitude modulation, and adds another signal that moves around in circles, so you get a Doppler frequency shift.<\/p>\n<p>If you compare the two, you can calculate the angle!<\/p>\n<h3 id=\"see-how-low-you-can-go-in-the-frequency-spectrum\">47: See how low you can go in the frequency spectrum<\/h3>\n<ul>\n<li><strong>Modulation:<\/strong> mostly AM<\/li>\n<\/ul>\n<p>This was a fun exploration: What\u2019s the lowest-frequency broadcast I can receive?<\/p>\n<p>The RTL-SDR Blog V4 stick I\u2019m using has a neat feature \u2013 a built-in \u201cupconverter\u201d, 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!<\/p>\n<p>The first stations that are comprehensible started at 1 MHz for me.<\/p>\n<p><video src=\"http:\/\/blinry.org\/cc5ff2908379955d.mp4\" controls><\/video><\/p>\n<h3 id=\"see-how-high-you-can-go-in-the-frequency-spectrum\">48: See how high you can go in the frequency spectrum<\/h3>\n<p>The chipset in my SDR stick go up to maximum frequency of 1766 MHz. 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.<\/p>\n<p>So the highest-frequency thing I\u2019ve received is ADS-B at 1090 MHz (see entry #5)! \ud83c\udf89<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/833875a5a00f9c32.png\" alt=\"software Three lines at around 1296 MHz.\" title=\"software Three lines at around 1296 MHz.\"><\/p>\n<h3 id=\"listen-to-marine-radio\">49: Listen to marine radio<\/h3>\n<p>We\u2019ve been over this. Not allowed in Germany. Don\u2019t do it. \u26d4<\/p>\n<p>But if you\u2019re in the US, anyone can purchase a marine radio, and even use it to transmit! \ud83d\ude00<\/p>\n<h3 id=\"go-mobile\">50: Go mobile!<\/h3>\n<p>Just now, I was wondering whether there are any Android apps for controlling SDRs.<\/p>\n<p>And it turned out, the software I liked best that week, SDR++, had an Android version since a couple of weeks! o\/<\/p>\n<p>So now I could go track down the source of some of these strange signals! :3<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/blinry.org\/50-things-with-sdr\/a8eec89128df1f90.jpeg\" alt=\"software Me, a red-haired, red-bearded white human, hold a smartphone, connected to a Framework module, connected to my SDR stick, connected to an antenna! I look happy and tired.\" title=\"software Me, a red-haired, red-bearded white human, hold a smartphone, connected to a Framework module, connected to my SDR stick, connected to an antenna! I look happy and tired.\"><\/p>\n<h2 id=\"looking-back\">Looking back<\/h2>\n<p>And with that, \u2026 \ud83e\udd41 \u2026 I was officially done with my \u201c50 things to do with a software defined radio\u201d! \ud83c\udf89<\/p>\n<p>This were seven very intense days, where I learned a lot of new things about radio waves and the many things they can be used for!<\/p>\n<p>I was proud! I was tired! I was amazed that all those things I received are all around us, everywhere, all at once \u2013 if you know where to look. :O<\/p>\n<h2 id=\"more-things-to-explore\">More things to explore<\/h2>\n<p>Here\u2019s some things that I haven\u2019t tried or that haven\u2019t worked:<\/p>\n<ul>\n<li>Receiving digital voice modes (SDRangel should be able to do it, but I couldn\u2019t figure it out)<\/li>\n<li>Receive something from the ISS<\/li>\n<li>Use the GRAVES radar to detect meteors (couldn\u2019t detect it)<\/li>\n<li>Receive videos on ham bands<\/li>\n<li>Receive Iridium satellites<\/li>\n<li>Listen to pirate stations<\/li>\n<li>Receive Cubesat<\/li>\n<\/ul>\n<p>Also, doing things with Wi-Fi\/Bluetooth\/Zigbee could be fun, but I\u2019d need a more expensive receiver for those frequencies.<\/p>\n<h2 id=\"future-thoughts\">Future thoughts<\/h2>\n<p>So, was this project in fact a gateway drug to getting an amateur radio license?<\/p>\n<p>Yeah, probably. I\u2019d love to transmit something and experiment more! \ud83d\ude00<\/p>\n<p>In Germany, a new license class will be introduced in summer 2024, that\u2019ll allow you to send on the 10-meter, 2-meter and 70-cm bands (the \u201cN class\u201d).<\/p>\n<p>In fact, there\u2019s a really good German online course that teaches you everything you need to know: 50ohm.de<\/p>\n<p>Highly recommended, even if you\u2019re not planning on getting a license.<\/p>\n<p>Finally, thanks to Piko, Chris, and Cqoicebordel for proof-reading this blog post! <3<\/p>\n<hr>\n<h2>Software Join the discussion!<\/h2>\n<p>\n                        You can add your comment<br \/>\n                        in the Fediverse!<br \/>\n                        Alternatively, drop me a mail at <span>m<span title=\"ihate@spam.com<\/span>&#8220;>a<\/span>il<\/span>@blinry<i title=\"<\/i>mailto:&#8221;>.<\/i>org.<br \/>\n                        Also, you can support me<br \/>\n                        on Patreon or<br \/>\n                        subscribe to my newsletter\n                    <\/p>\n<\/p><\/div>\n","protected":false},"excerpt":{"rendered":"<p>Software Last week, I went on an adventure through the electromagnetic spectrum! It\u2019s like an invisible world that always surrounds<\/p>\n","protected":false},"author":7282,"featured_media":13054,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-13053","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-software"],"_links":{"self":[{"href":"https:\/\/usaontheweb.com\/clone1\/wp-json\/wp\/v2\/posts\/13053","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/usaontheweb.com\/clone1\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/usaontheweb.com\/clone1\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/usaontheweb.com\/clone1\/wp-json\/wp\/v2\/users\/7282"}],"replies":[{"embeddable":true,"href":"https:\/\/usaontheweb.com\/clone1\/wp-json\/wp\/v2\/comments?post=13053"}],"version-history":[{"count":0,"href":"https:\/\/usaontheweb.com\/clone1\/wp-json\/wp\/v2\/posts\/13053\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/usaontheweb.com\/clone1\/wp-json\/wp\/v2\/media\/13054"}],"wp:attachment":[{"href":"https:\/\/usaontheweb.com\/clone1\/wp-json\/wp\/v2\/media?parent=13053"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/usaontheweb.com\/clone1\/wp-json\/wp\/v2\/categories?post=13053"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/usaontheweb.com\/clone1\/wp-json\/wp\/v2\/tags?post=13053"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}