SDR Scanner Listens To Everything

In the old days, scanners would listen to a bunch of channels in a round-robin fashion. If a signal breaks the squelch, the scanner stops and scanning continues scanning after a few seconds of inactivity. But with modern SDRs, you don’t have to listen to one channel at a time. You can listen to all of them. [Tech Minds] shows RTL-SDR Scanner on Linux to record up to 20 MHz of the band simultaneously. It records all the channels in the band of interest. The actual project is on GitHub.

Once recorded, you can use a web interface to listen to the channels and see some statistics about them. [Tech Minds] tried recording aircraft traffic. It worked, but the program doesn’t know how to demodulate AM yet so if you want to record the entire shortwave band, aircraft, or other AM sources, you’ll have to wait a bit before this software is ready for your use case.

If you need to run the program under Windows like [Tech Minds] did, you can use VMWare Workstation Player to get a free copy of Linux on Windows. We wondered if WSL version two might work, too, but we don’t know. Once you have Linux running, Docker makes the installation straightforward.  Since the interface is a web interface, you could probably run this on a small computer on the network and then access it at your leisure from another computer.

Of course, old-fashioned scanners were often used to listen to police and fire radios. Those have all gone trunked these days. This isn’t a new idea, but it did seem like a well-packaged solution.

39 thoughts on “SDR Scanner Listens To Everything

  1. Before there were scanners, you had to tune the band manually. Then somecrystal controlled radios. Then scanning added to those. But yiu needed to buy a crystal for every channel you wanted to listen to.

    Finally synthesized scanners. Tune any channel in the range. Though as I recall, more limited frequency range to.begin with. Some sidn’t even tune the aeroband.

    1. Because the aero band is AM, and everything else in the VHF is FM. Aero required a completely separate demodulator. Available for the price.
      Though, now it’s just a small matter of programming, and software is free, right?

    1. Bit optimistic to expect 20MHz out of a 3MHz device. Even 3MHz is a push, it has very low performance and it’s optimal at ~1.2MHz, but will be happy at 2.4MHz.

      Now, for 60MHz SDR for low cost then take a look at the RX888. That’s actually a nice SDR for a very reasonable price, but the bandwidth drops to 10MHz after 60MHZ.

  2. You use to be able to listen to public (police fire e.c.t) even when they were on trunked systems. unfortunately around here when APCO -p25 Motorola trunked systems rolled out they eventually started encrypting channels even those that shouldn’t have been encrypted. They want to force you to FOIA, which in itself requires you to know what your looking for, therefore someone inside would have to whistle blow before you even know what to request. It also presents a problem with discovery in part unless you get access to an axon body cam review with a link from {evidence} . com which also presents a questionable problem.

    1. Reason they’re encrypting – smart phone scanner apps.

      The knuckleheads at radio reference will argue to the contrary, but the fact of the matter is, they’re essentially destroying their own hobby by “streaming” scanner audio onto the internet – where anyone with a scanner app can listen.

      “back-in-the-day” the only way you could monitor is with a scanner in your town – as it should be. Why anyone would want to stream that audio so some noodnik on the other side of the country can listen in on it is beyond comprehension. What purpose does it serve ?

      All this has done is provide ample justification for adminstrators of these systems to encrypt the traffic – thereby preventing audio streaming. Many police chiefs have stated “scanner apps” are the primary reason they went to encryption.

      Sort of like what Lenin said – the capitalists well sell us the rope to hang themselves with.
      In the same vein, the scanner hobbyists streaming audio are slowly destroying their own hobby.

      1. Well said, as one we have to be more involved in the behavior of the A I brutal controls. The way that some ready to monetize for the few in control. By Enough of the police cam, control on phone computer and privacy policies.

      1. Do you live in a major municipality, or more rural? It seemed like the major cities converted too. Bigger budgets, but also more potential listeners.

        I thought some places fifty years ago used analog encoding. A balanced modulator and oscillator, and run in reverse on receive. Easy to build, and easy to figure out.

    2. There was a talk I found on Youtube back in ~2019 from Australia where a guy explained a weakness in P25 encryption that could get you in pretty easily, something along the lines of several 64-bit packets that only used 16 bits for data (rest were 0’s). He was able to get the keys within a day or so IIRC. The video must have been taken down because I have tried finding it several times with no luck.

        1. Try using Google itself with the “site” search modifier … For example:

          P25 encryption

          Most message boards have really crappy search basically based on Grep and I’ve found it is better to use Google with the site modifier to find things on those sites

      1. 40-bit ADP or DMR encryption can be cracked. One approach indeed uses the known plaintext silence packets as oracle. This is implemented in many signal intelligence tools. Of course the AES256 mode is way more secure.

        1. The Dept of Defense will stop efforts to put in the best encryption. You see they want to crack encryption of the bad guys. And strong encryption might have a customs block put in to disallow enemy countries from using it.

    3. Encryption is not something that’s guaranteed. They have to change the codes every so often, and other departments or talk groups are not going to be able to know the correct codes at all times, so usually in a major event they go open channel or use cell phones. They also can send messages using a data connection that is handled by the base station. As far as around here, NC State Police are using p25, but unencrypted. They can’t really encrypt it because the VIPER system makes it so you can talk to any radio in NC by hopping to repeaters. If you aren’t syncing encryption with everyone, it won’t work—so they just don’t.

  3. There are LOTS of SDR hardware receivers (some inexpensive, some not) out there, and also lots of free computer software to go with them. Most of the software I’ve seen allows you to record the entire received bandwidth and play it back later just as if you were hearing it for the first time. You can display it as a waterfall, tune to particular signals, and typically decode various modes. Several modern ham radio receivers even provide an I/Q output that can be directly processed by such software via a good sound card.

  4. WSL 2 as far as I know still does not allow usb devices unless you use the usb/ip kernel driver. Personally I’ve never tried that in wsl… anyone here have any luck with usb/ip and wsl?

    1. Apparently the US gov. had to fly a U-2S over it to intercept its satellite communications, which tells me it was probably spewing microwave and not RF, and probably with a very directional upward antenna.

      It’s still possible that an RF spectrum analyzer on the ground would have turned up something interesting though, so I share your curiosity.

  5. As a former 911 dispatcher, I can tell you the ONLY reason public
    safety encrypts “most” radio is to hide unethical/illegal “stuff”.
    There are a few exceptions, but very few.
    Heard it too many times. Believe what you want(head in sand).

      1. Are you claiming that because your coworkers have been shot and killed we should just abandon accountability for public servants and give complete blind trust to LEOs?
        I get the desire and need for operational security but ultimately you serve the public, not your own interests which means your actions, service, product, and even coms are public property.
        At best there should be selective use of encryption along with a very short timeframe from when that information isn’t deemed a risk to ongoing operations and then released to the public. Any attempt to delay, censor, slant, or impede the release of the obscured/encrypted coms after op sec necessity has pass should be met with immediate and severe consequences.
        Asking the public for greater while simultaneously claiming you can’t trust the general public is a nonstarter for a sincere discussion on this topic.

  6. Anyone in the radio industry knows why all radio communications havr gone digital. It is because of spectral efficiency! When police and fire need access to pictures of suspects or a building map of dangerous chemicals, it requires more bandwidth to send. Does the FCC just give away more spectrum for everyone to get their maps, or pictures, or webpage? No. They require you to use your 20 Mhz of spectrum digitally so as to communicate more, better, faster. Just like cellular. Original AMPS cellular was just FM and scanners could easily monitor. But then they went to 3G, and then 4G and now 5G. They can send many order of magnitude of data in the same spectrum. Police and fire are requiring the same improvement and the FCC is pushing public safety to do the same. Apco-25. Encryption is just a side benefit. There are SDR scanners for this encryption, but they take a large amount of space and power and money. They are considered illegal to own unless your are government agency. Used specifically to listen in on bad guys.

    1. It might suprise you to learn that police and firemen also have access to smartphones and tablets and don’t need some weird wireless setup to see pictures of suspects or bulding layouts or what have you.
      In fact they even have laptops too, go figure.

    2. Spectrum efficiency is correct, but they typically Google or call people and get email traffic for building layouts or special docs via smartphones now. They only use radios because it’s faster to push a button and yell when someone is shooting. Imagine dialing the station to report a active shooter, and the dispatch calling each car to send them out. It’s just easier with a radio that has a direct connection to the base.

  7. I am looking forward to a way to install in VMWare as Docker stalls and nothing will be installed. Sorry to say, but Linux is always a struggle by version of something not working properly…

    1. Will SDR Scanne be available for Windows in the future? I am endeed interresting :-)

      I now have SDR Scanner running on a RPi4, but it is unstable starting up as “sdr-sdr-monitor-reader-1” restarts over and over and over… ;-/

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