At the moment I have 5x RTL-SDR dongles streaming into a box on different bands (137, 433, 912, 978, and 1090 MHz). They pick up all kinds of things, from local weather stations to the water meter for my condo to ADS-B/UAT transmissions from local aircraft. I even see the tire pressure monitor signals from cars that drive by (some of you guys need to add air!).
Mostly it's just fun. I like peeking at all the ambient transmissions in the area.
A while back I was more deeply involved in the SDR space and even reverse-engineered some pager signals. At least a few years ago, pagers were still widely used in hospitals (totally in plaintext, by the way).
I’ve got one SDR reading air and VHF, one reading 1090 ADS-B, one on 433MHz reading weather stations, temp sensors, tire pressure modules, lots of stuff; finally a fourth one picking up local 70cm and 2m traffic. Oh and a GPS puck providing a stratum 1 time server. Lots of stuff to do and lots of exploring around your local bands.
Claude is surprisingly good at mapping out complex multi-repeater trunking systems, and identifying DMR vs P25 vs NXDN signals, so even if you know nothing about digital radio, you can be listening in minutes.
I am learning about radio and modulation using SDR (with professor Claude - incredible for learning! Especially if you know exactly what you want to learn and have a strong enough background in somewhat related fields - audio and image DSP for me - to make exercises it writes for me short, relatable, and yet illuminating) and our second lesson after cheap 433 remotes was FLEX and pagers - plenty of that stuff in the city, with about half messages from a hospital a few blocks away. Still very widely used in the US (I live in NYC).
Seeing what gets broadcasted there 100% unencrypted was quite a shock. Patient names, ages, and conditions; doctor names, rooms, departments, requests for medications and assistance... Insane amount of super private PII.
Learning the fundamentals behind radio really blew my mind at the time (years ago), and having Claude there to help visualize things must be an incredible boon.
Everything in SDR has an analog equivalent, from local oscillators to PLLs to filtering. In fact most of it simply is a direct implementation of decades-old analog concepts.
But the underlying math is what I found most incredible, where the "true" representation of a signal is complex, and that every real (both in the ordinary and mathematical sense) signal is actually the sum of a positive and negative frequency, such that the complex component cancels out. Phase becomes much more comprehensible as simply the angular component of the signal, and frequency is the derivative of phase. All of this had the indirect effect of improving my understanding of complex numbers as well.
off-topic, but "with professor Claude - incredible for learning! Especially if you know exactly what you want to learn "
This always strikes me in the "oh no look at all the cheating!" anti-ai takes.
Like, the cheating only blew up because there was/is the gap in teacher/professor/moderator understanding of the tools. Kids were copying wikipedia back in the day, and if the kid had a decent vocab, went completely undetected for a time. Then everyone thought they could do it and scorers got suspiscious enough to create a demand for an "is this wikipedia" software such that companies made them and scorers implemented them. We even saw reversions to written exams, and have had continuous use of written exams in 'critical' tests like SAT et al.
And of course, the only reason that the teacher's ensure that the students aren't cheating is because they know the students are heading for tests they can't cheat. So, there's new cheating, there will need to be new detection.
A motivated learner today has unprecedented capabilites compared to a motivated learner of even 10 years ago.
Assuming, of course, that the learner is practicing universally accepted study/research methods such as never implicitly trusting single sources, especially when they're third hand summaries of unverified sources.
I've had proffesors give me incorrect information with every bit of certainty an LLM offers, but it wouldn't be their fault if I just nodded along with either of them.
Many consumer temperature, humidity, rain, and wind sensors use simple radio protocols in the 433 MHz band to report their readings back to their indoor display unit.
Stick an RTL-SDR dongle on your computer and use the program rtl_433 to monitor that traffic. It comes with built-in decoders for the protocols for a very large number of those sensors.
I've got such a setup and I can see not only my one sensors (An AcuRite outdoor thermometer, and the two sensors from an AcuRite fridge/freeze thermometer) but also a few neighbor's temperature sensors, humidity sensors, soil moisture sensors, wind speed and direction sensors, rain gauges, and their tire pressure.
You can set up MQTT and have rtl_433 report the data that way, and you can have Home Assistant get that and display it. It knows how to handle a variety of sensor types.
I haven't done that yet. I just have rtl_433 log everything by appending JSON records to a file. A script reads that, finds the sensors I care about, and stores their data in an sqlite database.
It is cool to do. But there are professional uses for it, particularly like finding interference or noise. You can ask things like: "How crowded is my 2.4 GHz spectrum?"
The RTL SDR is the gateway drug into SDR's. The bandwidth is limited, so don't expect to be capturing HDTV Streams. But it's certainly possible to listen to AM/FM, Ham Bands, VHF/UHF signals, etc.
If you don't want to buy an RTL-SDR, you can search KiwiSDR which is a streaming SDR for frequencies under 30MHz. You can also connect to KiwiSDR's worldwide.
Then if you get the itch, you can go get your a HackRF, a ham license, or whatever else scratches it.
I've used it to identify transmissions in my neighborhood in the public (ISM) band, listen to various radio broadcasts outside the normal AM/FM, and best of all, track all the planes in my area (ADS-B).
At the moment I have 5x RTL-SDR dongles streaming into a box on different bands (137, 433, 912, 978, and 1090 MHz). They pick up all kinds of things, from local weather stations to the water meter for my condo to ADS-B/UAT transmissions from local aircraft. I even see the tire pressure monitor signals from cars that drive by (some of you guys need to add air!).
Mostly it's just fun. I like peeking at all the ambient transmissions in the area.
A while back I was more deeply involved in the SDR space and even reverse-engineered some pager signals. At least a few years ago, pagers were still widely used in hospitals (totally in plaintext, by the way).
I’ve got one SDR reading air and VHF, one reading 1090 ADS-B, one on 433MHz reading weather stations, temp sensors, tire pressure modules, lots of stuff; finally a fourth one picking up local 70cm and 2m traffic. Oh and a GPS puck providing a stratum 1 time server. Lots of stuff to do and lots of exploring around your local bands.
Claude is surprisingly good at mapping out complex multi-repeater trunking systems, and identifying DMR vs P25 vs NXDN signals, so even if you know nothing about digital radio, you can be listening in minutes.
I am learning about radio and modulation using SDR (with professor Claude - incredible for learning! Especially if you know exactly what you want to learn and have a strong enough background in somewhat related fields - audio and image DSP for me - to make exercises it writes for me short, relatable, and yet illuminating) and our second lesson after cheap 433 remotes was FLEX and pagers - plenty of that stuff in the city, with about half messages from a hospital a few blocks away. Still very widely used in the US (I live in NYC). Seeing what gets broadcasted there 100% unencrypted was quite a shock. Patient names, ages, and conditions; doctor names, rooms, departments, requests for medications and assistance... Insane amount of super private PII.
Learning the fundamentals behind radio really blew my mind at the time (years ago), and having Claude there to help visualize things must be an incredible boon.
Everything in SDR has an analog equivalent, from local oscillators to PLLs to filtering. In fact most of it simply is a direct implementation of decades-old analog concepts.
But the underlying math is what I found most incredible, where the "true" representation of a signal is complex, and that every real (both in the ordinary and mathematical sense) signal is actually the sum of a positive and negative frequency, such that the complex component cancels out. Phase becomes much more comprehensible as simply the angular component of the signal, and frequency is the derivative of phase. All of this had the indirect effect of improving my understanding of complex numbers as well.
off-topic, but "with professor Claude - incredible for learning! Especially if you know exactly what you want to learn "
This always strikes me in the "oh no look at all the cheating!" anti-ai takes.
Like, the cheating only blew up because there was/is the gap in teacher/professor/moderator understanding of the tools. Kids were copying wikipedia back in the day, and if the kid had a decent vocab, went completely undetected for a time. Then everyone thought they could do it and scorers got suspiscious enough to create a demand for an "is this wikipedia" software such that companies made them and scorers implemented them. We even saw reversions to written exams, and have had continuous use of written exams in 'critical' tests like SAT et al.
And of course, the only reason that the teacher's ensure that the students aren't cheating is because they know the students are heading for tests they can't cheat. So, there's new cheating, there will need to be new detection.
A motivated learner today has unprecedented capabilites compared to a motivated learner of even 10 years ago.
Assuming, of course, that the learner is practicing universally accepted study/research methods such as never implicitly trusting single sources, especially when they're third hand summaries of unverified sources.
I've had proffesors give me incorrect information with every bit of certainty an LLM offers, but it wouldn't be their fault if I just nodded along with either of them.
Many consumer temperature, humidity, rain, and wind sensors use simple radio protocols in the 433 MHz band to report their readings back to their indoor display unit.
Stick an RTL-SDR dongle on your computer and use the program rtl_433 to monitor that traffic. It comes with built-in decoders for the protocols for a very large number of those sensors.
I've got such a setup and I can see not only my one sensors (An AcuRite outdoor thermometer, and the two sensors from an AcuRite fridge/freeze thermometer) but also a few neighbor's temperature sensors, humidity sensors, soil moisture sensors, wind speed and direction sensors, rain gauges, and their tire pressure.
You can set up MQTT and have rtl_433 report the data that way, and you can have Home Assistant get that and display it. It knows how to handle a variety of sensor types.
I haven't done that yet. I just have rtl_433 log everything by appending JSON records to a file. A script reads that, finds the sensors I care about, and stores their data in an sqlite database.
It is cool to do. But there are professional uses for it, particularly like finding interference or noise. You can ask things like: "How crowded is my 2.4 GHz spectrum?"
The RTL SDR is the gateway drug into SDR's. The bandwidth is limited, so don't expect to be capturing HDTV Streams. But it's certainly possible to listen to AM/FM, Ham Bands, VHF/UHF signals, etc.
If you don't want to buy an RTL-SDR, you can search KiwiSDR which is a streaming SDR for frequencies under 30MHz. You can also connect to KiwiSDR's worldwide.
Then if you get the itch, you can go get your a HackRF, a ham license, or whatever else scratches it.
I've used it to identify transmissions in my neighborhood in the public (ISM) band, listen to various radio broadcasts outside the normal AM/FM, and best of all, track all the planes in my area (ADS-B).
Satdump group uses them receiving all kind of weather satellites. They are mastering S-/X-Band stuff for ages already.
Ham radio operators looking forward using them for 13cm and 5cm band stuff.