I got a walkie talkie set as a Christmas present when I was 8. Which was kind of an evil thing to do given I had no siblings or friends to play with. One day I turned one set on and listened for a while and I thought I heard someone talking behind all the static noise. So I said something and was shocked to hear the voice talking back to me. Fast forward a few decades, next week is my wedding and that voice on the other side of the radio is my best man.
My dad was a HAM (W7AAI) and as a kid I found the frequencies for walkie talkies on his receiver in the shack. After Christmas I would tune in and hear local kids doing the "I can hear you, can you hear me?" thing with the new presents.
my family had a little portable TV (GE 7-7150B, link below) that we'd usually only use down in the basement during severe weather.
one day I learned that you could tune in all sorts of non-TV frequencies. In particular, you could tune into any phone calls my neighbors were making on their wireless phones.
i loved that little tv and used it up until the conversion to digital OTA tranmissions.
I had a black and white solid state Sony TV in my bedroom when I was growing up.
Aside from dialing into late night TV programmes my parents prohibited, there were two buttons that switched between VHF and UHF.
Toggling the UHF button allowed me to tune into police radio.
Being able to capture this via that TV felt close to magic, and I think probably went a long way to forming my associations between technology, mystery and discovery.
Why was the title renamed on hacker news from “Fifty Things you can do with a Software Defined Radio” to Things you can do with a Software Defined Radio”?
Just curious about if the original title was rule breaking or something.
Here are some more things you can do with your RTL-SDR after the first 50:
Meteor weather satellite reception (Russian counterpart of the NOAA satellites, but digital, so higher res and in color)
Digital Radio Mondiale -- digital radio but for shortwave
Analog TV -- if you're in an area that still broadcasts this (unlikely), you can receive a black & white picture and closed captioning. If no OTA broadcasts remain, you can use the analog output of a VCR or DVD player
GPS -- rtlsdr is capable of decoding GPS, Galileo, and BeiDou! (Likely not GLONASS since each satellite uses a separate frequency, spreading the signal beyond the sdr's bandwidth)
Hidden secondary audio broadcasts inside FM radio (like the stereo audio hack, but using higher frequencies in the demodulated stream)
Brazilian outlaws and UHF pirates using open repeaters on US military satellites launched in the 70s
TEMPEST / "Van Eck phreaking" where you can remotely read a nearby screen due to leakage from the monitor or video cabling
Instrument landing system -- if you're near an airport you can tune to a runway's ILS frequency and see the signal change as you move from the left side of the runway to the right
Infrared remotes -- stick an IR photodiode in the antenna port and you can demodulate codes from remote controls
Passive radar -- Tune into a very narrowband signal like a VOR or ATSC pilot signal, set your decimation extremely high (i.e., trading bandwidth for dynamic range) and you can see nearby planes in the area from their doppler-shifted reflections of the main signal
The receiving IR remotes with an SDR by connecting an IR photodiode across the antenna input sounded like nonsense to me. I googled and could it be you meant people using the IR receiver feature of the RTLSDR's? It may still require connecting a photodiode, but to a different set of inputs.
As to connecting a photodiode to the antenna input, I don't see how that would work, but that may well be due to my limited understanding and imagination.
Do you mean using the photodiode in a photovoltaic mode? Also, presumably you'd have to bypass the tuner and hook to the direct sampling pins on an RTLSDR? Even with direct sampling, wouldn't the 38kHz of IR remote modulation get filtered out by the DC blocking?
A photodiode (BPV23NF iirc) connected straight to the dongle's SMA connector. Yes, I believe it would be operating in photovoltaic mode, where the incident IR light from the remote control will induce a small voltage. Yes, I had direct sampling mode turned on (but the rtl-sdr.com V3 can do this through the normal antenna port). I pointed the remote at the sensor (admittedly quite close) and saw a signal centered on 38 kHz in the waterfall, and was able to export the binary pulses.
I imagine, provided the IR's frequency can be sampled by the SDR, it would look like fairly wide band bursts that could be decoded? Especially if you just treat the SDR as a ADC Oscilloscope
It's not like you can apply a software security patch to a 1970's hardware communication device in orbit. They're likely going to continue acting as open repeaters until their orbit decays and they fall.
> Do you like feeling safe about leaving your expensive stuff in your hotel room? Have you ever had anything stolen out of your room, or discovered someone has gained access to your room while you weren't there? .. what about .. other rooms? Maybe not EXACTLY a hotel room? I've presented on securing hotel rooms in the past, but adding home assistant, zwave devices, co2 sensors and millimeter wave radar it's become a whole new game
> We use the GNURadio software along with RTL-SDR and ADALM-PLUTO hardware to explore the world of digital communication. We build up to a simple QPSK modem and rudimentary GPS reception.
> official [PlutoSDR] firmware updates are no longer focus on new features for SDR enthusiastic people.. tezuka.. aims to be Universal Zynq/AD9363 firmware builder for.. PlutoSDR, Pluto+, AntSDR (e200), LibreSDR
A few months ago when there was a lot of emergency services activity in my area and I didn't know why, I was reminded that no-one in my region is contributing a feed to Broadcastify.
I went down the tunnel of using SDR to recieve those transmissions, and share them online.
Then I went a bit further.
What if you could transcribe the broadcasts into something like a text feed? What if you could add location information somehow to monitor where things were going on in your region? Could you use AI to somehow organize the data into a more useful format?
What if this data was valuable? Maybe you could sell this as a service? Who would buy it? Public safety organizations? Hospitals? News organizations?
I spent a few days worth of freetime figuring out how you'd do someting like this, and got to a place where I figured it was conceptually possible.
Then somewhere in my googling, I stumbled across this site: http://citizen.com/ - and realized that someone had already turned my idea into what looks like a pretty mature product.
Ahh well. I'm sure my billion dollar idea will come later.
In the meantime, I'd still like to mess with SDR at least so I can know what's going on around me next time there's a fire or other public safety incident, before it gets reported on.
The fact that there's a mature product doing what you want to do is a good thing. It means there's a market for what you want that's large enough to sustain development.
You can easily distinguish yourself from Citizen by targeting a different demographic, different branding, different UX, interpreting the data in a different way.
Just look at how many businesses there are in any industry that deliver the same outcome for their customers but in a slightly different way.
What you're describing could be a really good news source giving live on-the-ground information to people.
I don't know about billion dollar ideas, but I encourage you to make a product even if something similar exists.
If you squint enough there is nothing new under the sun and chances are that you will take a very long time to find something that hasn't already been done!
But doing your own product does several things - you learn a lot, you position yourself for future success, you see future ideas differently. And maybe you're okay for something to not be a billion dollar idea and you can outlast a venture funded product.
Maybe I'm just projecting, because I've put of building something for such a long time!
My actual "MVP" was some kind of automated neighborhood newsletter, that'd monitor emergency services radio traffic, and put together some kind of "here's what happened in your neighborhood" daily newsletter.
Maybe I could get it packaged in a hardware/software package that let anyone set one up in their neighborhood.
But I mostly got stuck in privacy concerns. I'm not sure it's a valuable public service to let people know that, for example, someone had a heart attack a few blocks over.
I did think about the scientific value of some kind of statistical database that process and recorded emergency services calls though. But mostly, my ideas for commercial and moral opportunities were half-baked at the point that I discovered citizen.
One of the technical challenges I came up against was finding transcription software that could semi-accurately transcribe UHF/VHF radio traffic. However, it looks like there's some progress that's been made there since I last checked: https://www.rtl-sdr.com/radiotransciptor-real-time-radio-spe...
> But I mostly got stuck in privacy concerns. I'm not sure it's a valuable public service to let people know that, for example, someone had a heart attack a few blocks over.
In the moment, notifying people who know CPR and may be nearby and able to get to a nearby location and start CPR before emergency services arrives is the base of PulsePoint [1], which seems like a useful public service.
As a digest, yeah, I don't think any usefulness outweighs the invasion of privacy. Maybe just a count of health emergencies responded to for observing trends.
Many metro police are moving towards encrypted communications but it varies by location.
Regarding medical emergencies, I'm pretty sure EMS just says "medical emergency" and gives the address. I've never heard them say specific patient conditions, although sometimes the ambulance can forward that to the ER.
If there were any risk, it would be making it too easy for criminals to monitor and allow them to commit crime more effectively.
The privacy concern is real and not something I'd want to think about too hard myself. One night I heard sirens and checked one of the local scanner type sites. I could hear enough about the call, and that combined with a record of previous calls to that address made me wonder if I really wanted that information. Maybe some obfuscation of the previous codes to the address would have been enough to reduce the feeling of knowing too much.
None of that is to say it isn't a good idea. I appreciate the ability to see roughly what is going on when I hear sirens. Even if the sites aren't always able to show the calls. I think highway patrol doesn't show up for me.
I’d encourage you to pursue it.
I remember the old @breakingnews on Twitter when it first started, people listening to police scanners and typing info-dense one liners on what they heard. To this day the best news service of my life (until someone bought it).
A real time, AI snips version for my area in a running feed would be amazing. There are lots of formats and use cases; and the info is already out there.
It’s a great idea. Don’t let citizen sway you away from it.
> I encourage you to make a product even if something similar exists.
This is very good advice: we often give up on "great ideas" once we find that they have already been done.
But the vast majority of people we consider successful did not invent anything completely new, they just made a better kind of XYZ, sometimes not even that dramatically different. If you think about it, it's a much more logical path to success than expecting to be the next DaVinci.
Citizen is really enshittified, so any alternative would be better. I don’t object to them charging for their service, but they use all kinds of predatory editorial tactics and push notifications and marketing copy to instill primal fear that your neighborhood is imminently burning down and you will get shot if you don’t subscribe to a higher tier of service from them. Crime is way down in the US but you really don’t feel that way when you are a subscriber/user of Citizen.
Sadly, you can't really get NOAA satellite images any more. NOAA-15 and 19 were decommissioned August 19, 2025, and NOAA 18 was decommissioned in June. It's my understanding that you'll need a much more powerful antenna to get images from the new satellites. Still, SDR is great fun. It's incredible to realize that all this information is stored in electromagnetic waves and passing through us all the time.
About 24 years ago, I was working at Honeywell and they were pulling down data from the GOES satellites for use an a GA service. It required a giant satellite dish on the roof of the office building and a top-of-the-line (for the time) Pentium 4 for decoding.
I wonder what does it entail to have a NOAA satellite decommissioned? Is it just turned off or is it directed to fall down into a designated area in the Pacific?
They will continue to orbit for about 150 years, slowly falling towards earth until the drag from the atmosphere burns them up.
"Like many older satellites, the POES satellites do not have thrusters to support a controlled reentry into Earth’s atmosphere at the end of their mission life. Instead, once passivated, they are safely powered down, placed in a non-operational state, and left in a stable orbit. Without onboard propulsion or significant atmospheric drag at their current altitude, NOAA estimates they will remain in orbit for roughly 150 years before gradually reentering the atmosphere and disintegrating."[1]
There have been numerous issues in the past with 'dead' satellites waking back up and activating transmitters again, generally making a mess of the spectrum. Some satellites have pyro-fuses on the power lines from the solar arrays that are fired during passivation to make absolutely sure that the sat doesn't ever recharge and wakeup.
I agree they may want to reuse the spectrum, but I doubt it would be for a new satellite. At least not the stuff in the lower VHF band, around 137 MHz which is awfully close to the airband reservation used for VDL Mode 2 - around 135-137 MHz, IIRC. VDLM2 is in many ways a more modern ACARS.
They'd more likely use higher bands on newer satellites to get more throughput. The GOES birds transmit up around 1.7GHz, afaik and likely higher as well.
I depends on the orbit. The low Earth ones would usually be de-orbited and fall back to Earth. The geosychronous ones are usually just moved to a parking orbit out of the way to make room for more. If it's in a high but not very crowded orbit, they might just stop using it.
I was informed maybe 7 or 8 years back that my electric company would be replacing my analog meter with a smart one and always intended to try and glean more information about my electric consumption habits from it. It took me a lot longer than I intended, but last year I finally bought an RTL-SDR in the hopes of being able to get realtime info from the meter. Unfortunately, it seems that it's not one of the ones that emits consumption info over ISM bands for consumption by household appliances (so far as I can tell) and I ended up only capturing info from TPMS sensors off of passing cars (which was cool, but not really what I was looking for).
Do note that if you purchase an RTL-SDR these days, you'll probably get a v4 which, at least as of last year, does not play out-of-the-box at all with the software available on the Ubuntu apt repos and the RTL-SDR drivers that ship with 24.04 out-of-the-box — there were some hardware protocol/interface changes between v3 and v4 that make the old drivers incompatible and you'll get a litany of misleading or non-specific errors if you try without downloading and installing the latest drivers from GitHub (or somewhere).
Look into Rainforest Automation. I have their EMU-2 which can be paired with my electric meter. It spits out XML data which can be read by Home Assistant.
A number of smart meters communicate over the mains wires, especially when they're in very sparse areas. There was even a thought for a bit to offer internet services over the power distribution cables, but I don't think they ever really got effective data rates high enough to be competitive.
In the early 2000’s there were efforts to provide broadband over power lines (BPL). I think one of the biggest obstacles was the radio frequency interference it generated.
Re-reading some of the history of it that does sound like RF interference was more of a concern than data rates. Some places even attempted roll-outs but were stymied by regulators wanting more studies about potential impacts.
Yes, that seems to be what mine is doing as my ecobee thermostat is able to read info about peak usage times from the mains. I didn't know about the latter part though, I never imagined electric companies were making a play for the internet (though it seems like an obvious thought in retrospect).
A lot of electric companies in the US are also ISPs. They already have most of the equipment to run fiber, and many also do wireless links between substations.
If it's low enough bitrate, wouldn't you be able to read that by putting an antenna or loop of wire near the mains? I assume they use a documented standard.
And its "last mile" friend of using the in-wall cable as Ethernet drops, too, e.g. https://www.tp-link.com/us/powerline/ (but I don't think it holds a candle to actually pulling cat 5 or 6, for clarity)
The paging system was unencrypted around here the last I looked (that was during covid). And there was software that could decode the transmissions. The SDR would easily pick it up.
One of the hospitals had been using it and would page people with PII -- including which people were in which room. So you could kinda see what was happening in the hospitals -- particularly during covid.
There kinda was a life cycle, seeing people admitted, O2 alerts firing off, and then the morgue being called to a room.
Overall, it was both interesting to have insight into something that you weren't ever going to be allowed to have access, and also very very sad.
Listening to pagers is illegal in US from ECPA of 1986. It is the same law that banned listening to the analog cell frequencies, which still applies even thought that is long gone.
There is no way that they will know or care if you don't share messages.
Same experience here with hospital pagers. I tried this way back in 2013 when I first started with SDR. Even without covid, the messages were hideous and depressing. Not recommended.
I concur, but for a different reason. This is repeating a narrative that was found to be a policy decision by hospitals in the US. That sentence isn't quite right but i don't have time to formulate it better.
The pocsag data, if this detailed, would have mentioned giving specific patients specific medicine that would then cause their O2 sat to drop. Since that isn't mentioned, either they forgot, or maybe there's an axe to grind.
Nevertheless, having grabbed pocsag in my area i don't remember seeing much PII, mostly room numbers, if anything.
Receiving 433Mhz sensor data using rtl_433[0] with an RTL SDR was a lot of fun when I started doing it last year. There's MQTT output if you want to send it to Home Assistant, et. al., as well as simple text output to stdout. It was great fun seeing my neighbors' sensors, tire pressure sensors in passing vehicles, etc.
There a ton of devices that use 433Mhz. You can also extend rtl_433 pretty easily.
A lot of the 433/915 band devices you can pick up with rtl_433 seem to be much more bullet proof and have longer battery life than equivalent WiFi and Zigbee devices too. Building new protocol decoders for rtl_433 also surprisingly isn't too bad either. One of my favorite ones is the water meter decoder which has saved me a lot of money when I've had irrigation water leaks and not noticed them (but saw conspicuous usage patterns reported).
ive got ~15 deployed sensors/transmitters and I haven't touched a single one in 14 months since initial setup. its super reliable if you can get your receiver/antenna somewhere that works well.
I'm spoiled. One of my receivers is on a second story and has great line-of-sight to a bunch of houses and a parking lot (where I assume I get a lot of my TPMS "hits").
I was able to read some data from my electric meter, but the good stuff is encrypted.
What I was _really_ hoping to read was my water meter. It transmits so infrequently, though, so it's hard get much of anything or even know if you're successfully receiving something more than noise.
I've been going down this rabbit hole, there are two alternative options if you're looking for a side project, 1 is "ai on the edge" (Google it it's a pretty cool project), which is basically an esp32 + camera that takes a photo of your meter on a regular basis and OCRs the data, option 2 is (and I'll be trying this this week) to get a magnetometer hooked up to an esp32 to read the little magnetic pulses the impeller (in my case) makes (which is how the meter hardware they have reads it anyway), can have calibration difficulties but will be so cheap, there are also existing esphome projects for this.
Astonishing! Thank you very much for sharing..
This sentence really stuck out for me - "I was proud! I was tired! I was amazed that all those things I received are all around us, everywhere, all at once – if you know where to look. :O"
A few years ago I used an RTL-SDR to determine if I had a water leak since my meter is one that broadcasts over 900mhz (iirc). I wrote a small program to parse RTL-AMR output into Prometheus metrics (real life gauges are just like Prometheus gauges, who would've thought) and tracked it over a week while I was away on vacation. No leak luckily.
I've been wanting to experiment with SDR triangulation. There are some off the shelf options, but I think it would be fun to cobble something together using dongles.
For triangulation though, if you have a reference signal at a known location, TDoA (time difference of arrival) requires less hardware (just a single receiver at each location, e.g. an RTL-SDR). I don't know of any open-source software which does that though I've been slowly building some for my own use (it's pretty janky at the moment).
I want to experiment with stationary receivers around the perimeter of my property. It would be fun to document and pinpoint every RF source on my land, but I'd settle for being able to reliably find my dog.
Ah TDoA might not have the resolution you need for that, unless you are working with very wideband signals. Probably ~100 m resolution is the best you can get from it.
One of the people in my local radio club did a demonstration of tracking down a commercial operation using amateur radio frequencies with the KrakenSDR. It's very impressive. I think the timing would be much more difficult using off the shelf dongles.
This page was very slow to load for me, probably partly because it's being hugged by HN. But it would help a lot if images had the `loading="lazy"` attribute, and if they were compressed to about ~100KiB each instead.
Hope they have an unlimited bandwidth plan. I bailed out at about #20, which is unfortunate because it's otherwise a nice list. I'm going to assume 51. Get a Free Kia, isn't part of it.
What's even more interesting about this is that anyone flying their own personal plane would generally be expected to be listening to others on their same frequency (and sometimes this helps prevent accidents). So in that sense, the ATC messages are "meant for any member of the public who happens to be flying a plane nearby".
But apparently the government of Germany doesn't quite conclude the same thing from that which I do.
Similarly, the government of Germany (apparently?) seem to make the distinction that decoding signals from a neighbors IoT device is not restricted like other "messages not meant for the general public", so honestly there's probably a lot of nuance that a naive outsider is completely missing.
Warning: My German legalese isn't very good and this is not legal advice. I unfortunately know very little about how the German court system works and where to look up stuff.
The law[1] is worded like this:
> (1) Mit einer Funkanlage (§ 3 Absatz 1 Nummer 1 des Funkanlagengesetzes) dürfen nur solche Nachrichten abgehört oder in vergleichbarer Weise zur Kenntnis genommen werden, die für den Betreiber der Funkanlage, für Funkamateure im Sinne des § 2 Nummer 1 des Amateurfunkgesetzes, für die Allgemeinheit oder für einen unbestimmten Personenkreis bestimmt sind.
The law basically says that you may only listen to (or take note of in comparable way[2]) messages that are:
1. For you, the operator
2. For amateur radio operators according to the Amateurfunkgesetz
3. For the general public
4. For an indeterminate group of persons (I think that's an accurate translation?)
For me, a big question regarding aviation and marine traffic monitoring is what "unbestimmten Personenkreis"/"indeterminate group of persons" actually means. Since "die Allgemeinheit"/"the general public" is listed separately, I'd assume it's a distinct group from that, and to me the previous commenter's "meant for any member of the public who happens to be flying a plane nearby" sounds like it could fit that description. I'd argue, for example, that police radio is for a "determinate" group of persons, police officers and dispatchers working for the government, whereas aviation and maritime traffic is an "indeterminate" group of people, people working for all sorts of airlines, shipping companies, recreational pilots/boaters, who happen to be around the same area.
If anyone has any links to cases where this law was tried in relation to aviation or maritime communications, please share them, I have been struggling to figure out where to look for this stuff, on top of that, the law was also renamed or moved around, which makes it extra confusing.
[2] Might be related to this weird ruling, where a judge in a case about some ADS-B receiver decided that it was ok because rendering the position of aircraft wasn't "listening to" (as in, literally hearing) the traffic: https://openjur.de/u/130555.html - This decision is probably moot now, due the addition of "take note of in comparable way". The judge briefly mentions that actually listening to the traffic could be violating the law, but I am not sure if this point was ever properly litigated.
Note for anyone trying to receive lower frequency signals (below 10MHz): The supplied coaxial cable is really really lossy at those frequencies, a change of cable ought to make a big difference in what you receive.
I bought myself a Baofeng & a Quansheng radio just recently & love to hear aviation conversations & such .. sadly I wasnt't able to hear anyone else yet .. on PMR nor Freenet
Super interesting !
If you want to hear amateur radio conversations, check for regularly scheduled 'nets' in your area. Search for "$yourcity amateur radio club" and they'll probably have some details.
I cant speak to 2G networks, but 5G (and 4G) are amazingly simple to get started using OpenAirInterface. With a USRP B210 I had a 5G network running from a bare Ubuntu install in under 30 minutes. I used a smartphone and some cheap (blank, user-writable) SIM cards to connect and test it.
Over a decade ago I played with SDR sharp and a tv dongle and got to listen to very cool stuff. I don’t know if SDR sharp still exists, I think it was closed source at the time but free. I remember one could use it to decode stuff and then map to virtual ports to redirect to other software that expected an input from specialized hardware like ship signals and stuff like that.
People are commenting about issues loading the images leading to them abandoning reading the article. Here is a fully cached copy of TFA, but note that the videos (and images, but especially the videos) load _really_ slowly https://web.archive.org/web/20240317122351/https://blinry.or... (but they do load if you wait long enough).
How does one use random wire antenna in an urban area!
Tried once and just got huge amount of noise all over HF. Except for a few strong shortwave and Amateur Radio stations, the rest of HF was pretty useless.
TL,DR: you probably don't want a random wire for HF reception, but either an E-field whip antenna like that one, or an H-field loop which will likely be larger and more expensive, but will have useful directional properties that the whip will not.
Gabe just quit his dayjob to go full-time on SaveItForParts, so hopefully we'll be seeing even more cool stuff in the near future. Me personally, I'm hoping for a collab between him and Jeff. They've had some interaction already (Jeff donated Gabe a spare computer he had lying around) so maybe... That would be epic if it did happen.
Like 13 years ago when I was doing FPV I remember soldering my own skew-planar/quadrifilar antennas with bendable wire ha, the photo of the short yellow dipole reminded me of it. I think it's a dipole or double-dipole not sure.
more than 15 years ago I got a chance to play with gnu radio and back then it was hailed as the next big industry.. fast forward, and beyond the hacking community (and the hobbyist), it still has not taken over.
My impression is that gnuradio is fine for prototyping/poc, but has issues in its design when you try and run production workloads with more complex workflows (ie, writing custom Mac layers/ workflows that involve heavy feedback, etc. you end up having to do a a lot of hacking around with the message passing infrastructure).
That being said last I used it extensively was v3 so maybe v4 is better. Did they get rid of thread per block and allow you to have a single thread service a sub signal chain? I remember that the number of context switches between threads, and balancing latency vs buffer sizes was a pain in the rear.
The threading model is still difficult, and it's still enough slower that thinking you're going to be comparable to custom silicon that's been designed for a particular protocol is silly.
It's great fun for doing signal analysis, but I'd never want to try and implement a full-duplex communication system in production with it.
FWIW, if you have an SDR that doesn't work with the frequency you want to work with, you may be able to use an up-converter or down-converter in front of the SDR to shift the frequency enough to work. There are ones like the Ham It Up[1], etc. that may be appropriate depending on the circumstances. Or you could possibly build your own.
You can get an AD9363 clone of the USRP b210 online for like, 300 USD?
The AD9363 stock is only supposed to be 325mhz to 3.8ghz but stuff like the plutoSDR which uses it manages to get the transceiver all the way from 70mhz to 6ghz like the more expensive AD9361 used in the real USRP B210s
Benefit is you can transmit stuff too, not just receive unlike the RTL-SDR which is RX only
Is there anything like this that can go down to 15 MHz or lower? including transmit and several analog modes of modulation USB LSB NFM WFM AM CW at least
Groovy. Are there any limiting factors such as processor speed and what is the best software that does it all on Linux? I have no idea what ratio of magic smoke is in the software vs. ratio of magic smoke is in the hardware.
The output of a usb radio like this is a set of IQ values which is the raw data from the ADC. The amount of values (samples) you get is device dependent and also limited by your interface. The RTL SDR 4 over usb can do up to 2.4-3.5MHz. The ADC on that device is 8 bit so you will get two 8 bit, IQ numbers per sample.
You can tune into remote SDR’s people set up to work with this data without having your own device or download recordings others have made.
It is this raw sample data that you then demodulate according to whatever scheme required on the PC side.
A great resource I found was pysdr.org. I had absolutely no background in RF and very little python experience but that guide explains everything from the ground up from how the IQ samples are physically generated and read in an antenna, all the modulation schemes you mentioned, and how to code useful things with the various devices. No affiliation but a great resource.
for anyone reading this actually interested, just FYI an improved model "HackRF Pro" is due for release in the next month or so, is backwards-compatible, and is what will come in at that $400 price tag.
years ago, there used to be a very abundant market for used or chinese clone HackRF One units, but i haven't been able to find any these days.
Quite a few radar systems are in the 8-10GHz range and satellite communications just above that. The general idea when using a SDR for these things is to have a separate frequency converter & amplifier at the antenna feed itself, then have an intermediate frequency <6GHz fed via cable to the SDR. Tends to be much easier and cheaper this way.
480 Mbps is plenty for low GHz signals. 1GHz gives you 20MHz to play with, which turns into about ~100 Mbps max. A 6GHz signal pulling out all the stops will give you at ~1.6Gbps, but if you're dealing with data that extreme you're barking up the wrong tree with a cheap SDR like the HackRF.
I got a walkie talkie set as a Christmas present when I was 8. Which was kind of an evil thing to do given I had no siblings or friends to play with. One day I turned one set on and listened for a while and I thought I heard someone talking behind all the static noise. So I said something and was shocked to hear the voice talking back to me. Fast forward a few decades, next week is my wedding and that voice on the other side of the radio is my best man.
Congrats! That's such a cool story!
>Fast forward a few decades, next week is my wedding and that voice on the other side of the radio is...
I think I've seen too many rom-coms because I was sure this sentence going to end with "my fiance." : )
Ten years ago I proposed to my best friend.
She said no.
Does a hollywood movie with that plot exist?
Sorry to hear that.
Are you willing to say what happened afterwards?
Are you still friends?
Plot Twist AF… you could be a writer
My dad was a HAM (W7AAI) and as a kid I found the frequencies for walkie talkies on his receiver in the shack. After Christmas I would tune in and hear local kids doing the "I can hear you, can you hear me?" thing with the new presents.
my family had a little portable TV (GE 7-7150B, link below) that we'd usually only use down in the basement during severe weather.
one day I learned that you could tune in all sorts of non-TV frequencies. In particular, you could tune into any phone calls my neighbors were making on their wireless phones.
i loved that little tv and used it up until the conversion to digital OTA tranmissions.
[0]: https://www.youtube.com/watch?v=N4qYPLd8owc
I had a black and white solid state Sony TV in my bedroom when I was growing up.
Aside from dialing into late night TV programmes my parents prohibited, there were two buttons that switched between VHF and UHF.
Toggling the UHF button allowed me to tune into police radio.
Being able to capture this via that TV felt close to magic, and I think probably went a long way to forming my associations between technology, mystery and discovery.
I expected the voice on the other side being your soon-to-be wife. But good story nevertheless. Congrats!
I thought the same thing. But it does happen, my neighbors started dating and eventually married after meeting over ham radio.
Just think about all of the weather and doctors appointments they can talk about now!
Awesome story and well told
This is awesome, and future congratulations on your wedding!
damn, that's awesome.. I feel like I just watched the opening scene of a nice "stand by me" type movie.
This is awesome, and congratulations!
I got chills reading this. Congrats!
Why was the title renamed on hacker news from “Fifty Things you can do with a Software Defined Radio” to Things you can do with a Software Defined Radio”?
Just curious about if the original title was rule breaking or something.
SDR is amazing!
Here are some more things you can do with your RTL-SDR after the first 50:
Meteor weather satellite reception (Russian counterpart of the NOAA satellites, but digital, so higher res and in color)
Digital Radio Mondiale -- digital radio but for shortwave
Analog TV -- if you're in an area that still broadcasts this (unlikely), you can receive a black & white picture and closed captioning. If no OTA broadcasts remain, you can use the analog output of a VCR or DVD player
GPS -- rtlsdr is capable of decoding GPS, Galileo, and BeiDou! (Likely not GLONASS since each satellite uses a separate frequency, spreading the signal beyond the sdr's bandwidth)
Hidden secondary audio broadcasts inside FM radio (like the stereo audio hack, but using higher frequencies in the demodulated stream)
Brazilian outlaws and UHF pirates using open repeaters on US military satellites launched in the 70s
TEMPEST / "Van Eck phreaking" where you can remotely read a nearby screen due to leakage from the monitor or video cabling
Instrument landing system -- if you're near an airport you can tune to a runway's ILS frequency and see the signal change as you move from the left side of the runway to the right
Infrared remotes -- stick an IR photodiode in the antenna port and you can demodulate codes from remote controls
Passive radar -- Tune into a very narrowband signal like a VOR or ATSC pilot signal, set your decimation extremely high (i.e., trading bandwidth for dynamic range) and you can see nearby planes in the area from their doppler-shifted reflections of the main signal
The receiving IR remotes with an SDR by connecting an IR photodiode across the antenna input sounded like nonsense to me. I googled and could it be you meant people using the IR receiver feature of the RTLSDR's? It may still require connecting a photodiode, but to a different set of inputs.
https://medium.com/@rxseger/receiving-ir-signals-with-rtl-sd...
As to connecting a photodiode to the antenna input, I don't see how that would work, but that may well be due to my limited understanding and imagination.
Do you mean using the photodiode in a photovoltaic mode? Also, presumably you'd have to bypass the tuner and hook to the direct sampling pins on an RTLSDR? Even with direct sampling, wouldn't the 38kHz of IR remote modulation get filtered out by the DC blocking?
A photodiode (BPV23NF iirc) connected straight to the dongle's SMA connector. Yes, I believe it would be operating in photovoltaic mode, where the incident IR light from the remote control will induce a small voltage. Yes, I had direct sampling mode turned on (but the rtl-sdr.com V3 can do this through the normal antenna port). I pointed the remote at the sensor (admittedly quite close) and saw a signal centered on 38 kHz in the waterfall, and was able to export the binary pulses.
This video shows a Passive RF/Fiber connector that seems to work pretty reliably for broadcast tv.
https://www.youtube.com/watch?v=wIN7DVGBbKM
I imagine, provided the IR's frequency can be sampled by the SDR, it would look like fairly wide band bursts that could be decoded? Especially if you just treat the SDR as a ADC Oscilloscope
> Brazilian outlaws and UHF pirates using open repeaters on US military satellites launched in the 70s
This is still happening? I'm sorry but that's hilarious!
https://www.wired.com/2009/04/fleetcom/
It's not like you can apply a software security patch to a 1970's hardware communication device in orbit. They're likely going to continue acting as open repeaters until their orbit decays and they fall.
Displaying malicious image causes HDMI cable to emit LoRa packets, https://github.com/XieyangSun/TEMPEST-LoRa
"Build a passive radar with software-defined radio" (2022), https://hn.algolia.com/?query=passive%20radarSEC-T 0x11 (2025) on evil maid defense, https://www.youtube.com/watch?v=ScwNIWzk4RQ
> Do you like feeling safe about leaving your expensive stuff in your hotel room? Have you ever had anything stolen out of your room, or discovered someone has gained access to your room while you weren't there? .. what about .. other rooms? Maybe not EXACTLY a hotel room? I've presented on securing hotel rooms in the past, but adding home assistant, zwave devices, co2 sensors and millimeter wave radar it's become a whole new game
Video tutorial series with book references, https://gallicchio.github.io/learnSDR/:> We use the GNURadio software along with RTL-SDR and ADALM-PLUTO hardware to explore the world of digital communication. We build up to a simple QPSK modem and rudimentary GPS reception.
LibreSDR firmware, https://github.com/F5OEO/tezuka_fw
> official [PlutoSDR] firmware updates are no longer focus on new features for SDR enthusiastic people.. tezuka.. aims to be Universal Zynq/AD9363 firmware builder for.. PlutoSDR, Pluto+, AntSDR (e200), LibreSDR
A few months ago when there was a lot of emergency services activity in my area and I didn't know why, I was reminded that no-one in my region is contributing a feed to Broadcastify.
I went down the tunnel of using SDR to recieve those transmissions, and share them online.
Then I went a bit further.
What if you could transcribe the broadcasts into something like a text feed? What if you could add location information somehow to monitor where things were going on in your region? Could you use AI to somehow organize the data into a more useful format?
What if this data was valuable? Maybe you could sell this as a service? Who would buy it? Public safety organizations? Hospitals? News organizations?
I spent a few days worth of freetime figuring out how you'd do someting like this, and got to a place where I figured it was conceptually possible.
Then somewhere in my googling, I stumbled across this site: http://citizen.com/ - and realized that someone had already turned my idea into what looks like a pretty mature product.
Ahh well. I'm sure my billion dollar idea will come later.
In the meantime, I'd still like to mess with SDR at least so I can know what's going on around me next time there's a fire or other public safety incident, before it gets reported on.
The fact that there's a mature product doing what you want to do is a good thing. It means there's a market for what you want that's large enough to sustain development.
You can easily distinguish yourself from Citizen by targeting a different demographic, different branding, different UX, interpreting the data in a different way.
Just look at how many businesses there are in any industry that deliver the same outcome for their customers but in a slightly different way.
What you're describing could be a really good news source giving live on-the-ground information to people.
I don't know about billion dollar ideas, but I encourage you to make a product even if something similar exists.
If you squint enough there is nothing new under the sun and chances are that you will take a very long time to find something that hasn't already been done!
But doing your own product does several things - you learn a lot, you position yourself for future success, you see future ideas differently. And maybe you're okay for something to not be a billion dollar idea and you can outlast a venture funded product.
Maybe I'm just projecting, because I've put of building something for such a long time!
I was joking about the billion dollar idea.
My actual "MVP" was some kind of automated neighborhood newsletter, that'd monitor emergency services radio traffic, and put together some kind of "here's what happened in your neighborhood" daily newsletter.
Maybe I could get it packaged in a hardware/software package that let anyone set one up in their neighborhood.
But I mostly got stuck in privacy concerns. I'm not sure it's a valuable public service to let people know that, for example, someone had a heart attack a few blocks over.
I did think about the scientific value of some kind of statistical database that process and recorded emergency services calls though. But mostly, my ideas for commercial and moral opportunities were half-baked at the point that I discovered citizen.
One of the technical challenges I came up against was finding transcription software that could semi-accurately transcribe UHF/VHF radio traffic. However, it looks like there's some progress that's been made there since I last checked: https://www.rtl-sdr.com/radiotransciptor-real-time-radio-spe...
> But I mostly got stuck in privacy concerns. I'm not sure it's a valuable public service to let people know that, for example, someone had a heart attack a few blocks over.
In the moment, notifying people who know CPR and may be nearby and able to get to a nearby location and start CPR before emergency services arrives is the base of PulsePoint [1], which seems like a useful public service.
As a digest, yeah, I don't think any usefulness outweighs the invasion of privacy. Maybe just a count of health emergencies responded to for observing trends.
[1] https://www.pulsepoint.org/
Many metro police are moving towards encrypted communications but it varies by location.
Regarding medical emergencies, I'm pretty sure EMS just says "medical emergency" and gives the address. I've never heard them say specific patient conditions, although sometimes the ambulance can forward that to the ER.
If there were any risk, it would be making it too easy for criminals to monitor and allow them to commit crime more effectively.
The privacy concern is real and not something I'd want to think about too hard myself. One night I heard sirens and checked one of the local scanner type sites. I could hear enough about the call, and that combined with a record of previous calls to that address made me wonder if I really wanted that information. Maybe some obfuscation of the previous codes to the address would have been enough to reduce the feeling of knowing too much.
None of that is to say it isn't a good idea. I appreciate the ability to see roughly what is going on when I hear sirens. Even if the sites aren't always able to show the calls. I think highway patrol doesn't show up for me.
I’d encourage you to pursue it. I remember the old @breakingnews on Twitter when it first started, people listening to police scanners and typing info-dense one liners on what they heard. To this day the best news service of my life (until someone bought it).
A real time, AI snips version for my area in a running feed would be amazing. There are lots of formats and use cases; and the info is already out there.
It’s a great idea. Don’t let citizen sway you away from it.
> I encourage you to make a product even if something similar exists.
This is very good advice: we often give up on "great ideas" once we find that they have already been done.
But the vast majority of people we consider successful did not invent anything completely new, they just made a better kind of XYZ, sometimes not even that dramatically different. If you think about it, it's a much more logical path to success than expecting to be the next DaVinci.
Citizen is really enshittified, so any alternative would be better. I don’t object to them charging for their service, but they use all kinds of predatory editorial tactics and push notifications and marketing copy to instill primal fear that your neighborhood is imminently burning down and you will get shot if you don’t subscribe to a higher tier of service from them. Crime is way down in the US but you really don’t feel that way when you are a subscriber/user of Citizen.
That was the vibe I was getting when visiting the site, they seem to understand fear pretty well. Stay away for your own mental health :-)
Sadly, you can't really get NOAA satellite images any more. NOAA-15 and 19 were decommissioned August 19, 2025, and NOAA 18 was decommissioned in June. It's my understanding that you'll need a much more powerful antenna to get images from the new satellites. Still, SDR is great fun. It's incredible to realize that all this information is stored in electromagnetic waves and passing through us all the time.
You can buy the kit on Amazon for the GOES satellites. Pretty easy to do
https://a.co/d/d7pCLGd
About 24 years ago, I was working at Honeywell and they were pulling down data from the GOES satellites for use an a GA service. It required a giant satellite dish on the roof of the office building and a top-of-the-line (for the time) Pentium 4 for decoding.
I wonder what does it entail to have a NOAA satellite decommissioned? Is it just turned off or is it directed to fall down into a designated area in the Pacific?
They will continue to orbit for about 150 years, slowly falling towards earth until the drag from the atmosphere burns them up.
"Like many older satellites, the POES satellites do not have thrusters to support a controlled reentry into Earth’s atmosphere at the end of their mission life. Instead, once passivated, they are safely powered down, placed in a non-operational state, and left in a stable orbit. Without onboard propulsion or significant atmospheric drag at their current altitude, NOAA estimates they will remain in orbit for roughly 150 years before gradually reentering the atmosphere and disintegrating."[1]
[1] https://www.nesdis.noaa.gov/news/legacy-orbit-noaa-decommiss...
It sucks they power it down
Probably to recover the frequency for a newer satellite. The spectrum they transmit on is quite scarce.
How locked down are they? Should I expect to see a hacker conference talk "how i revived a weather satellite"?
Maybe once they're turned off they're irrecoverable?
There have been numerous issues in the past with 'dead' satellites waking back up and activating transmitters again, generally making a mess of the spectrum. Some satellites have pyro-fuses on the power lines from the solar arrays that are fired during passivation to make absolutely sure that the sat doesn't ever recharge and wakeup.
It's not impossible
https://www.youtube.com/watch?v=HT2i7mFpFxM
I agree they may want to reuse the spectrum, but I doubt it would be for a new satellite. At least not the stuff in the lower VHF band, around 137 MHz which is awfully close to the airband reservation used for VDL Mode 2 - around 135-137 MHz, IIRC. VDLM2 is in many ways a more modern ACARS.
They'd more likely use higher bands on newer satellites to get more throughput. The GOES birds transmit up around 1.7GHz, afaik and likely higher as well.
You have to have an antenna pointing at the satellite though. That's an additional layer of selectivity.
Makes total sense, thank you
I depends on the orbit. The low Earth ones would usually be de-orbited and fall back to Earth. The geosychronous ones are usually just moved to a parking orbit out of the way to make room for more. If it's in a high but not very crowded orbit, they might just stop using it.
Where can I find more info about this? Ie: type of antenna needed, etc?
Oh that's too bad, I had done this in the past and it was good fun.
I was informed maybe 7 or 8 years back that my electric company would be replacing my analog meter with a smart one and always intended to try and glean more information about my electric consumption habits from it. It took me a lot longer than I intended, but last year I finally bought an RTL-SDR in the hopes of being able to get realtime info from the meter. Unfortunately, it seems that it's not one of the ones that emits consumption info over ISM bands for consumption by household appliances (so far as I can tell) and I ended up only capturing info from TPMS sensors off of passing cars (which was cool, but not really what I was looking for).
Do note that if you purchase an RTL-SDR these days, you'll probably get a v4 which, at least as of last year, does not play out-of-the-box at all with the software available on the Ubuntu apt repos and the RTL-SDR drivers that ship with 24.04 out-of-the-box — there were some hardware protocol/interface changes between v3 and v4 that make the old drivers incompatible and you'll get a litany of misleading or non-specific errors if you try without downloading and installing the latest drivers from GitHub (or somewhere).
Look into Rainforest Automation. I have their EMU-2 which can be paired with my electric meter. It spits out XML data which can be read by Home Assistant.
https://www.rainforestautomation.com/rfa-z105-2-emu-2-2/
I have a v5 and have had no issues with Fedora 42 btw. Worked out of the box.
When I was installing it I actually came across the Ubuntu installation notes only to find I didn't need to do any of those things on my systems.
I believe the v5 is a Nooelec and is comparable to the RTL v3. The RTL v4 is the latest chip. They both have different strengths and weaknesses tho.
https://www.onesdr.com/rtl-sdr-vs-nesdr-which-one-should-i-b...
> capturing info from TPMS sensors off of passing cars
... sitting on a porch, yelling "Check your tires!" at random cars...
A number of smart meters communicate over the mains wires, especially when they're in very sparse areas. There was even a thought for a bit to offer internet services over the power distribution cables, but I don't think they ever really got effective data rates high enough to be competitive.
In the early 2000’s there were efforts to provide broadband over power lines (BPL). I think one of the biggest obstacles was the radio frequency interference it generated.
Re-reading some of the history of it that does sound like RF interference was more of a concern than data rates. Some places even attempted roll-outs but were stymied by regulators wanting more studies about potential impacts.
https://en.wikipedia.org/wiki/Broadband_over_power_lines
Thanks for correcting me on that.
Yes, that seems to be what mine is doing as my ecobee thermostat is able to read info about peak usage times from the mains. I didn't know about the latter part though, I never imagined electric companies were making a play for the internet (though it seems like an obvious thought in retrospect).
A lot of electric companies in the US are also ISPs. They already have most of the equipment to run fiber, and many also do wireless links between substations.
If it's low enough bitrate, wouldn't you be able to read that by putting an antenna or loop of wire near the mains? I assume they use a documented standard.
And its "last mile" friend of using the in-wall cable as Ethernet drops, too, e.g. https://www.tp-link.com/us/powerline/ (but I don't think it holds a candle to actually pulling cat 5 or 6, for clarity)
Heya, author here! This was such a fun project, and I'd really recommend the "Make 50 Things of Something" technique to everyone!
Also, I gave a 10-minute talk version of this post at !!Con last year: https://www.youtube.com/watch?v=Xic63tHw2Bo
[delayed]
I’ve been wanting to buy a cheap dongle to play around this stuff. Cool to see an inspiring article. Anyone got suggestions for a simple SDR?
I think you could also receive this direct broadcast: https://user.eumetsat.int/data/satellites/metop-sg/metop-sg-...
The paging system was unencrypted around here the last I looked (that was during covid). And there was software that could decode the transmissions. The SDR would easily pick it up.
One of the hospitals had been using it and would page people with PII -- including which people were in which room. So you could kinda see what was happening in the hospitals -- particularly during covid.
There kinda was a life cycle, seeing people admitted, O2 alerts firing off, and then the morgue being called to a room.
Overall, it was both interesting to have insight into something that you weren't ever going to be allowed to have access, and also very very sad.
Listening to pagers is illegal in US from ECPA of 1986. It is the same law that banned listening to the analog cell frequencies, which still applies even thought that is long gone.
There is no way that they will know or care if you don't share messages.
Same experience here with hospital pagers. I tried this way back in 2013 when I first started with SDR. Even without covid, the messages were hideous and depressing. Not recommended.
very unlikely. you may have read some text pages but not enough to get anywhere near the type of picture you're claiming.
I concur, but for a different reason. This is repeating a narrative that was found to be a policy decision by hospitals in the US. That sentence isn't quite right but i don't have time to formulate it better.
The pocsag data, if this detailed, would have mentioned giving specific patients specific medicine that would then cause their O2 sat to drop. Since that isn't mentioned, either they forgot, or maybe there's an axe to grind.
Nevertheless, having grabbed pocsag in my area i don't remember seeing much PII, mostly room numbers, if anything.
Receiving 433Mhz sensor data using rtl_433[0] with an RTL SDR was a lot of fun when I started doing it last year. There's MQTT output if you want to send it to Home Assistant, et. al., as well as simple text output to stdout. It was great fun seeing my neighbors' sensors, tire pressure sensors in passing vehicles, etc.
There a ton of devices that use 433Mhz. You can also extend rtl_433 pretty easily.
[0] https://github.com/merbanan/rtl_433
A lot of the 433/915 band devices you can pick up with rtl_433 seem to be much more bullet proof and have longer battery life than equivalent WiFi and Zigbee devices too. Building new protocol decoders for rtl_433 also surprisingly isn't too bad either. One of my favorite ones is the water meter decoder which has saved me a lot of money when I've had irrigation water leaks and not noticed them (but saw conspicuous usage patterns reported).
ive got ~15 deployed sensors/transmitters and I haven't touched a single one in 14 months since initial setup. its super reliable if you can get your receiver/antenna somewhere that works well.
WAY cheaper than the other options too.
I was hoping to find more devices around me which use 433. Apparently my neighbors don't have any 433MHz devices.
I'm spoiled. One of my receivers is on a second story and has great line-of-sight to a bunch of houses and a parking lot (where I assume I get a lot of my TPMS "hits").
I was able to read some data from my electric meter, but the good stuff is encrypted.
What I was _really_ hoping to read was my water meter. It transmits so infrequently, though, so it's hard get much of anything or even know if you're successfully receiving something more than noise.
I've been going down this rabbit hole, there are two alternative options if you're looking for a side project, 1 is "ai on the edge" (Google it it's a pretty cool project), which is basically an esp32 + camera that takes a photo of your meter on a regular basis and OCRs the data, option 2 is (and I'll be trying this this week) to get a magnetometer hooked up to an esp32 to read the little magnetic pulses the impeller (in my case) makes (which is how the meter hardware they have reads it anyway), can have calibration difficulties but will be so cheap, there are also existing esphome projects for this.
They replaced my older style meter, the kind that you have, with a Sensus Iperl.
https://www.xylem.com/en-us/products--services/metrology-equ...
I know that it has a radio, but it might only transmit when it receives a signal from a vehicle driving down the street.
Astonishing! Thank you very much for sharing.. This sentence really stuck out for me - "I was proud! I was tired! I was amazed that all those things I received are all around us, everywhere, all at once – if you know where to look. :O"
Related. Others?
Fifty Things you can do with a Software Defined Radio - https://news.ycombinator.com/item?id=39728153 - March 2024 (40 comments)
A few years ago I used an RTL-SDR to determine if I had a water leak since my meter is one that broadcasts over 900mhz (iirc). I wrote a small program to parse RTL-AMR output into Prometheus metrics (real life gauges are just like Prometheus gauges, who would've thought) and tracked it over a week while I was away on vacation. No leak luckily.
RTL-AMR: https://github.com/bemasher/rtlamr
Cool!
I can highly recommend the book Practical SDR if you want to learn about SDR: https://nostarch.com/practical-sdr
I've been wanting to experiment with SDR triangulation. There are some off the shelf options, but I think it would be fun to cobble something together using dongles.
https://www.crowdsupply.com/krakenrf/krakensdr
https://khanfar-spectrum-analyzer.web.app/ also has some phase-based direction-finding software and upcoming hardware.
For triangulation though, if you have a reference signal at a known location, TDoA (time difference of arrival) requires less hardware (just a single receiver at each location, e.g. an RTL-SDR). I don't know of any open-source software which does that though I've been slowly building some for my own use (it's pretty janky at the moment).
You could perhaps compare notes with the author of [0] who did manage to achieve multilateration with rtl-sdrs using TDoA.
[0] https://jenda.hrach.eu/
Oh wow that's a fantastic resource thank you!
I want to experiment with stationary receivers around the perimeter of my property. It would be fun to document and pinpoint every RF source on my land, but I'd settle for being able to reliably find my dog.
Ah TDoA might not have the resolution you need for that, unless you are working with very wideband signals. Probably ~100 m resolution is the best you can get from it.
One of the people in my local radio club did a demonstration of tracking down a commercial operation using amateur radio frequencies with the KrakenSDR. It's very impressive. I think the timing would be much more difficult using off the shelf dongles.
This page was very slow to load for me, probably partly because it's being hugged by HN. But it would help a lot if images had the `loading="lazy"` attribute, and if they were compressed to about ~100KiB each instead.
Hope they have an unlimited bandwidth plan. I bailed out at about #20, which is unfortunate because it's otherwise a nice list. I'm going to assume 51. Get a Free Kia, isn't part of it.
I always forget that the US still has bandwidth caps.. something which has never really existed where I live for fixed broadband.
Server bandwidth wherever he's hosted.
I don't think it's very common anymore.
Is it clear that the aviation or maritime communications are "not meant for the public" within the meaning of the German law?
I'm amazed to see that liveatc.net has no receivers in Germany, maybe a sign that other people also have this interpretation of the legislation?
What's even more interesting about this is that anyone flying their own personal plane would generally be expected to be listening to others on their same frequency (and sometimes this helps prevent accidents). So in that sense, the ATC messages are "meant for any member of the public who happens to be flying a plane nearby".
But apparently the government of Germany doesn't quite conclude the same thing from that which I do.
Similarly, the government of Germany (apparently?) seem to make the distinction that decoding signals from a neighbors IoT device is not restricted like other "messages not meant for the general public", so honestly there's probably a lot of nuance that a naive outsider is completely missing.
Warning: My German legalese isn't very good and this is not legal advice. I unfortunately know very little about how the German court system works and where to look up stuff.
The law[1] is worded like this:
> (1) Mit einer Funkanlage (§ 3 Absatz 1 Nummer 1 des Funkanlagengesetzes) dürfen nur solche Nachrichten abgehört oder in vergleichbarer Weise zur Kenntnis genommen werden, die für den Betreiber der Funkanlage, für Funkamateure im Sinne des § 2 Nummer 1 des Amateurfunkgesetzes, für die Allgemeinheit oder für einen unbestimmten Personenkreis bestimmt sind.
The law basically says that you may only listen to (or take note of in comparable way[2]) messages that are:
1. For you, the operator
2. For amateur radio operators according to the Amateurfunkgesetz
3. For the general public
4. For an indeterminate group of persons (I think that's an accurate translation?)
For me, a big question regarding aviation and marine traffic monitoring is what "unbestimmten Personenkreis"/"indeterminate group of persons" actually means. Since "die Allgemeinheit"/"the general public" is listed separately, I'd assume it's a distinct group from that, and to me the previous commenter's "meant for any member of the public who happens to be flying a plane nearby" sounds like it could fit that description. I'd argue, for example, that police radio is for a "determinate" group of persons, police officers and dispatchers working for the government, whereas aviation and maritime traffic is an "indeterminate" group of people, people working for all sorts of airlines, shipping companies, recreational pilots/boaters, who happen to be around the same area.
If anyone has any links to cases where this law was tried in relation to aviation or maritime communications, please share them, I have been struggling to figure out where to look for this stuff, on top of that, the law was also renamed or moved around, which makes it extra confusing.
[1] https://dejure.org/gesetze/TDDDG/5.html
[2] Might be related to this weird ruling, where a judge in a case about some ADS-B receiver decided that it was ok because rendering the position of aircraft wasn't "listening to" (as in, literally hearing) the traffic: https://openjur.de/u/130555.html - This decision is probably moot now, due the addition of "take note of in comparable way". The judge briefly mentions that actually listening to the traffic could be violating the law, but I am not sure if this point was ever properly litigated.
Germany signed the Rome treaty so you can legally ignore that bullshit law.
>Klaus, Bernd, Jürgen and Horst were talking about antennas, relays, and Windows XP!
I was last active on HAM bands about 15 years ago, but that sounds about right. And the weather.
Note for anyone trying to receive lower frequency signals (below 10MHz): The supplied coaxial cable is really really lossy at those frequencies, a change of cable ought to make a big difference in what you receive.
I bought myself a Baofeng & a Quansheng radio just recently & love to hear aviation conversations & such .. sadly I wasnt't able to hear anyone else yet .. on PMR nor Freenet Super interesting !
If you want to hear amateur radio conversations, check for regularly scheduled 'nets' in your area. Search for "$yourcity amateur radio club" and they'll probably have some details.
I have a USRP B210 and its great fun for many things. One of my favorite things to do is create a small 2G GSM base station to use old phones!
You say this as if it's an easy thing anybody might do -- like putting flowers in a vase in the kitchen. Isn't it pretty complicated?
I cant speak to 2G networks, but 5G (and 4G) are amazingly simple to get started using OpenAirInterface. With a USRP B210 I had a 5G network running from a bare Ubuntu install in under 30 minutes. I used a smartphone and some cheap (blank, user-writable) SIM cards to connect and test it.
Over a decade ago I played with SDR sharp and a tv dongle and got to listen to very cool stuff. I don’t know if SDR sharp still exists, I think it was closed source at the time but free. I remember one could use it to decode stuff and then map to virtual ports to redirect to other software that expected an input from specialized hardware like ship signals and stuff like that.
There is SDR++ : https://www.sdrpp.org/
https://archive.today/T0q8E
https://web.archive.org/web/20250908132643/https://blinry.or...
"Listening to “messages not meant for the general public” is not allowed in Germany, so of course I didn’t do that"
The treaty of Rome says otherwise. Germans too are free to receive.
I have been feeding ADSB data to public feeds for almost two years now: https://i.imgur.com/p9dRiVP.png
It runs on an Orange Pi Zero 3 SBC.
People are commenting about issues loading the images leading to them abandoning reading the article. Here is a fully cached copy of TFA, but note that the videos (and images, but especially the videos) load _really_ slowly https://web.archive.org/web/20240317122351/https://blinry.or... (but they do load if you wait long enough).
How does one use random wire antenna in an urban area!
Tried once and just got huge amount of noise all over HF. Except for a few strong shortwave and Amateur Radio stations, the rest of HF was pretty useless.
Even had decent ground plane and tuned it.
For HF, look at the technical articles by PA3WFM for the WebSDR at utwente.nl, especially this one: https://www.pa3fwm.nl/technotes/tn07.html
TL,DR: you probably don't want a random wire for HF reception, but either an E-field whip antenna like that one, or an H-field loop which will likely be larger and more expensive, but will have useful directional properties that the whip will not.
Very cool post. If Jeff Geerling is reading this, I wouldn't mind watching a video on each of these ;)
Check out saveitforparts on youtube, he does lots of this stuff.
Gabe just quit his dayjob to go full-time on SaveItForParts, so hopefully we'll be seeing even more cool stuff in the near future. Me personally, I'm hoping for a collab between him and Jeff. They've had some interaction already (Jeff donated Gabe a spare computer he had lying around) so maybe... That would be epic if it did happen.
They already did a quick collab with Jeff's PIs in space video. But I'm definitely hoping for more.
Aaah. I haven't watched that one yet, so I didn't even know. I'll definitely check that out later today.
Like 13 years ago when I was doing FPV I remember soldering my own skew-planar/quadrifilar antennas with bendable wire ha, the photo of the short yellow dipole reminded me of it. I think it's a dipole or double-dipole not sure.
edit: I think it's just a dipole
more than 15 years ago I got a chance to play with gnu radio and back then it was hailed as the next big industry.. fast forward, and beyond the hacking community (and the hobbyist), it still has not taken over.
It's super popular within the RF industry.
But for the normal users - to be honest - most topics are too heavy on complex math. And there's no way to avoid it if you want results.
Most advanced radio stuff much more complicate than checking out a repo from GitHub and compiling it.
My impression is that gnuradio is fine for prototyping/poc, but has issues in its design when you try and run production workloads with more complex workflows (ie, writing custom Mac layers/ workflows that involve heavy feedback, etc. you end up having to do a a lot of hacking around with the message passing infrastructure).
That being said last I used it extensively was v3 so maybe v4 is better. Did they get rid of thread per block and allow you to have a single thread service a sub signal chain? I remember that the number of context switches between threads, and balancing latency vs buffer sizes was a pain in the rear.
The threading model is still difficult, and it's still enough slower that thinking you're going to be comparable to custom silicon that's been designed for a particular protocol is silly.
It's great fun for doing signal analysis, but I'd never want to try and implement a full-duplex communication system in production with it.
If I were doing SDR-based comms in production, a custom C (or C++) application would be on the table, and nothing else.
Kudos on convincing me to try one of these dongles. This looks like a ridiculously fun project to do with the kids.
What a great write. I fiddled around with RTL SDRs years ago, but never got so far.
Pictures are loading at a crawl, had to bail because the layout kept rerendering.
Looks like hug of death strikes again!
Nice blog. It would be great if there was a table of contents to see everything at a glance.
Is there SDR for the GHz range of signals used by modern equipment?
FWIW, if you have an SDR that doesn't work with the frequency you want to work with, you may be able to use an up-converter or down-converter in front of the SDR to shift the frequency enough to work. There are ones like the Ham It Up[1], etc. that may be appropriate depending on the circumstances. Or you could possibly build your own.
[1]: https://www.nooelec.com/store/sdr/sdr-addons/ham-it-up.html
You can get an AD9363 clone of the USRP b210 online for like, 300 USD?
The AD9363 stock is only supposed to be 325mhz to 3.8ghz but stuff like the plutoSDR which uses it manages to get the transceiver all the way from 70mhz to 6ghz like the more expensive AD9361 used in the real USRP B210s
Benefit is you can transmit stuff too, not just receive unlike the RTL-SDR which is RX only
Is there anything like this that can go down to 15 MHz or lower? including transmit and several analog modes of modulation USB LSB NFM WFM AM CW at least
If I understand what you're saying, you can do any modulation scheme with sdr, it doesnt depend on the model
Groovy. Are there any limiting factors such as processor speed and what is the best software that does it all on Linux? I have no idea what ratio of magic smoke is in the software vs. ratio of magic smoke is in the hardware.
The output of a usb radio like this is a set of IQ values which is the raw data from the ADC. The amount of values (samples) you get is device dependent and also limited by your interface. The RTL SDR 4 over usb can do up to 2.4-3.5MHz. The ADC on that device is 8 bit so you will get two 8 bit, IQ numbers per sample.
You can tune into remote SDR’s people set up to work with this data without having your own device or download recordings others have made.
It is this raw sample data that you then demodulate according to whatever scheme required on the PC side.
A great resource I found was pysdr.org. I had absolutely no background in RF and very little python experience but that guide explains everything from the ground up from how the IQ samples are physically generated and read in an antenna, all the modulation schemes you mentioned, and how to code useful things with the various devices. No affiliation but a great resource.
HackRF One can go up to 6GHz ($400 new or $100 on alibaba for a similar device). Any higher frequency than that you'll be paying thousands.
for anyone reading this actually interested, just FYI an improved model "HackRF Pro" is due for release in the next month or so, is backwards-compatible, and is what will come in at that $400 price tag.
years ago, there used to be a very abundant market for used or chinese clone HackRF One units, but i haven't been able to find any these days.
Yeah I dont know any SDR above 6GHZ but also other than mmwave 5G I also dont know much radio that is above 6Ghz in general
Quite a few radar systems are in the 8-10GHz range and satellite communications just above that. The general idea when using a SDR for these things is to have a separate frequency converter & amplifier at the antenna feed itself, then have an intermediate frequency <6GHz fed via cable to the SDR. Tends to be much easier and cheaper this way.
Here you go, from the US perspective:
https://www.ntia.gov/files/ntia/publications/2003-allochrt.p...
Looks cool, except it uses USB2 which seems limiting in view of bandwidth.
480 Mbps is plenty for low GHz signals. 1GHz gives you 20MHz to play with, which turns into about ~100 Mbps max. A 6GHz signal pulling out all the stops will give you at ~1.6Gbps, but if you're dealing with data that extreme you're barking up the wrong tree with a cheap SDR like the HackRF.
"modern equipment" uses all KINDS of different frequencies, so that statement doesn't mean anything :/
Why not, if you want to address all those frequencies you need the highest capability, so GHz range not MHz range.
Kudos! I needed a break from no.24 and am looking forward to reading the remaining uses. Awesome article and resource. Thank you.
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wow