SDR as a Police and Fire radio scanner

If you’ve lost interest in that DVB dongle you bought to give software defined radio a try you should bust it back out. [Harrison Sand] just finished a guide on how to use SDR to listen in on Police and Fire radio bands.

The project, which results in the crystal clear audio reception heard after the break, uses a whole lists of packages on a Windows box to access the emergency bands. SDRSharp, which has been popular with other DVB dongle hacks, handles the hardware work. In this case the dongle is a Newsky TV28T v2 module that he picked up for a few bucks. He’s also using some support programs including the Digital Speech Decoder which turns the data into audio.

We wonder how many areas this will work for. It was our understanding that law enforcement was moving to encrypted communications systems. But all we really know about it is that you can jam the system with a children’s toy.

47 thoughts on “SDR as a Police and Fire radio scanner

  1. This is really amazing, if your area is on a P25 digital trunk system. I’ve been enjoying the city of Cincinnati’s P25 digital as a source of great entertainment. Having a 2nd tuner dedicated for the control frequency really helps this setup in terms of responsiveness. Disable UAC and run as admin for all programs involved (SDR#, Unitrunker, DSD) if issues arrise.

    1. I’m amazed there are any trunked P25 systems that aren’t encrypted. Pretty well all of the systems in major cities in Australia are now (or will be soon) encrypted, so I suppose enjoy it while it lasts.

      1. it’s funny twenty-seven countries in europe can agreed in use same band using an ETSI standard (TETRA), meanwhile in USA one PD can’t talk with neighbouring city PD.

        1. It’s not that they can’t agree on a standard. It’s that departments are funded separately. The state police might want to upgrade their system and tell everybody to use “Encrypted Gizmo 2013” but that means now the County Sheriff dept. and the local Police have to buy all new equipment for their handhelds and vehicles. The local PD might barely have enough money to operate and can’t afford new radios. That’s not to mention the federal agencies involved either.

          I’m 99% they’d all be using the same standard if every time the protocol switched the federal government would buy the radios for everybody.

        2. Actually my example is Australia. Also TETRA is really the defacto standard for modern 2-way communication, it’s just a question of who will pay for the infrastructure. In Great Britain the Airwave project was created in a public-private partnership which has the overseeing entity Airwave Solutions making money hand over fist every time anyone in the country hits the PTT button. In Australia the states have taken a dim view of going to the extent to encrypt communications and then route it through infrastructure owned by a private company, so instead they setup their own.

          There’s no doubt the entire state will move to the same system eventually (in this case P25) however the move will take time. Also just because systems are not the same doesn’t mean you can’t bridge between them. We do this where I work, we bridge a local legacy Motorola Smartnet system to a Motorola TETRA system and to a MotoTRBO system 15km down the road owned and operated by another company with whom we have to remain in constant communication.

          It’s a question of money, not standards.

  2. This post was worth reading just to find out about SDR# — I guess its time to break out the tuner again and try it.

    In the video, is the channel automatically going to the signal with the peak level, or is the user manually switching channels?

    I wish somebody would come up with a GNU or free version of Virtual Audio Cable, though. I’d kinda like to actually use the fancy audio subsystem on my new laptop in Windows (it is a corporate laptop, or otherwise it would have gone Linux the first week I had it).

    1. Per the article, the channel switching is being done automatically… the channel it keeps going back to is the control channel and it reads that to determine which active channel to switch to for the parts of the conversations. when speech is done on the active channel, the softwar switches back to the control channel to listen for the next notification. Pardon me if I didn’t use the right lingo, but that’s the jist of it. :-)

  3. i got one of these dongles through amazon for use with SDR, it works pretty good, but the antenna could use a little work, otherwise its a great dongle and couppled with SDR# makes a great combination

  4. Years back I had rabbit ears hooked to a WinTV tuner card and found some mode in the software to let me tune by frequency. The frequencies were offset, but I was able to listen to local radio stations(even though the card I owned didn’t officially support radio) as well as tune into the local FD and PD signal.

    1. Yes thought you don’t need to install half the software on the list. Air traffic including approach channels and local airport information are all broadcast in analogue. Just install SDR# Zadig and the driver and poke around somewhere just above FM radio.

  5. I’m using an RTL2832/E4000-based DVB-T dongle from Europe, and the IF noise(presumably) is just horrible. Spikes every 28kHz or so across the whole 2MHz slice… and the thing gets hot after a while. And the stock antenna does suck… I don’t even think the “coax” is shielded. Its only about 1/16″ diameter. I had an old scanner mast dipole I broke out and ran RG-6 to it with a PAL(Bellman-Hughes or whatever) to F adapter. That vastly improved things as far the noise floor, but the spikes are still there(not to mention the huge LO spike in the middle). I personally use HDSDR but SDR# is good, too… just not as much eye-candy.

    I’m planning on building a 125MHz NE/SA602-based upconverter for tuning HF and I’m thinking of putting the dongle in the box so I can isolate it from and RF and provide some forced-air cooling. I’m gonna throw in a 1:1 balun/isolator on the inputs, just for S&G. Plus, if the dongle is in the box, I can provide it with a better ground than going though the guts of the computer through the USB.

    I’m having a bitch of a time sourcing a 125MHz oscillator that’s not SMD, though. I’ve never done SMD and I’m not sure if I’m really equipped for it. Soldering a bacon-bit isn’t exactly something I look forward to. I would much rather have a DIP-4 package. But Mouser stopped stocking them.

    1. You sure those spikes are noise and not a function of the poor hardware dongle itself? I get the same thing when tuning in certain frequencies and I highly doubt the government would tolerate this kind of interference near airtraffic bands where I experience it. I am about to try a different dongle because of this.

      Also I suggest try the SMD route. You may like it. It really is quite easy and the only special tool you need is a set of tweezers. Even a standard soldering iron is fine for SMD work, though the finer the tip the easier it is.

    2. My results are similar to yours. I solved this by isolating the power from USB and also putting the unit in a shielded enclosure. The “” site has a good one. Have not yet tried a down converter to tune in HF, but there are ready made ones for about $50 USD available.

      1. Kendall: Thanx! I completely forgot eBay!

        Garbz: I think they are indeed specifically from poorly filtered/shielded oscillator. It turns out the oscillator for this thing is 28.8kHz. It’s worse in certain bands(like 2m 144-148MHz) I call the spikes noise because that’s what they are. Anything not a real signal is noise, including that caused by the hardware itself. In this case, I believe the term is “image noise”, in this case. In other words, yes, it’s the POS dongle I have :) As far as SMD goes, my hands aren’t the steadiest anymore…


        Steve: That is indeed my plan. And it’s an UPconverter; bringing the HF(DC-60Mhz) signals up to the range of the receiver(~60-2200MHz), while keeping those signals out of the FM broadcast band(88-108MHz)… so that the HF will be tunable by the receiver software(HDSDR) with a -125MHz offset (125-180MHz). I’m a little worried about the low HF… I’m 1/4 mile from an AM broadcast station. I occasionally hear it on my telephone and speakers(without being hooked up… it’s spooky as hell walking into a room and hearing voices on a disconnected speaker!)

        The design I am basing the upconverter off of is that by W9RAN(featured in January 2013 QST and available for $40 in kit… but I need to customize with compartmentalized shielding and stuff, and it includes manual bypass of the upconverter(separate HF, VHF/UHF antenna inputs). Another possible project is a downconverter for snagging signals over 2200MHz… but I’ll need to lose the noise first, and I think an LNB would work for that… but it’s not high on the priorities list.

        In building the HF upconverter, I’m going to need to have an internal 7805 to power the NE/SA602, and I was going to feed the dongle with that instead of the power from the USB. Basically, I am going to solely have the two data channels and the ground channel on the USB(I don’t like seeing isolated ground planes, plus it’s needed by the data channels). I would just connect to the computer at the box instead of at the dongle in one nice, clean package.

        After this, the next project would be an SDR transmitter stage, which I would incorporate with the receiver project stage to have a fully-functional transceiver. I just wish HRD supported SDRs other than Flex. Maybe I’ll have to throw an ARM in there to simulate a known transceiver as far as the CAT software is concerned.

    1. Check out Osmocom’s Tetra project, I can attest to the fact that it demodulates Tetra just fine having used it for ham radio. I don’t know the compatibility between this and the cheap USB SDRs but it works just fine with the FCD Pro.

    2. Also one caveat to the above is that it does not decrypt signals, however I believe the only people who do encrypt are the Brits, Belgians and Dutch. The latter 2 use static keys, Brits rotate keys at irregular periods.

  6. “The project, which results in the crystal clear audio reception” So how did they fix the super garbage receiver in these things? They dont add any hardware to compensate for the useless antenna, and almost deaf frontend.

    1. Another brilliant comment brought to you by fartface the troll who quite clearly has no clue given how the signal received appears to be some 30dB above the noise floor.

      Given how you normally bitch and moan about hacks being too expensive why do you suddenly suggest spending money where it’s clearly not needed? Has all the trolling finally rotted your brain? … I mean more than it already was.

  7. Someone Needs To do this for the Raspberry Pi… Im making a carputer, navigation and radio/videos. but im a volenteer firefighter and it would be nice to get the page threw the car radio.
    next steps would be decode the data for the location and put it straite into the navigation system.

  8. Hi would like to know a lot more iam in England so I take it that’s not p25 trunk please tell me what I would need to know to set up on my lap top I notice a Aries some sort mag mount

    1. Sorry not much of a computer  guy  but I like information  so if I seam to don’t understand  sorry and be patient  with me thanks Mike from uk

      Sent from Samsung Mobile on O2

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