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diff --git a/_posts/2020-06-26-police-scanner-setup.md b/_posts/2020-06-26-police-scanner-setup.md new file mode 100644 index 0000000..dde7e1e --- /dev/null +++ b/_posts/2020-06-26-police-scanner-setup.md @@ -0,0 +1,170 @@ +--- +layout: default +title: "Setting Up A Police Scanner With An RTL-SDR" +--- + +so my city has a community-run police scanner broadcast on the internet, but +the person who runs it is a bootlicker who's been threatening to shut it down +if people are using it to make trouble for the cops. so i figured i'd set up my +own. this is how i did it, hope it's useful. + +## shopping +you'll need [an RTL-SDR unit][rtl-sdr]. i recommend the dipole antenna kit as +well, so you don't need to make any additional purchases. if you're a radio +enthusiast already, you might have a better antenna available, but if you're +like me you do not and it's worth the US$10. mine took a bit over a week to +arrive. if you're extremely unlucky, you might need two of them, but i was fine +with just one. + +[rtl-sdr]: https://www.rtl-sdr.com/buy-rtl-sdr-dvb-t-dongles/ + +## basic setup +once your RTL-SDR arrives, you'll want to put together your antenna. if you're +lucky, like i am, you can just extend the antennas arbitrarily and it'll work +fine; if you're cursed, the RTL-SDR website has resources on how long is ideal +for various frequencies. + +connect the antenna to the RTL-SDR unit, plug it in, and follow the RTL-SDR +[quick start guide][qsg]. SDRSharp will work, or any of the other Windows +options. some of what we'll need is only available on windows. + +once your RTL-SDR's drivers are sorted out, find the specifications for police +radio in your area on [RadioReference][]. click your state, click your county, +scroll down and see if there's a link above a frequency table for you. if +you're lucky, there is, and if you click it there's a page with a table with +System Type and System Voice entries at the top. mine has a system type of +EDACS Networked Standard and a system voice of ProVoice and Analog, so the rest +of this assumes that's what you've got as well. if not, good luck. + +there should be a table for System Frequencies on your RadioReference page. +start up SDRSharp and tune your radio to the first frequency listed there. +you'll probably hear a bunch of static and the UI will look something like +this: + + + +see how there's one constant signal and a bunch of other signals that appear +and disappear all over the place? well, that's trunking, and the constant +signal is our *control channel*. if you don't see it, you can click and drag on +the bottom axis of the top panel to change the view. once you've found that +constant signal, click on it to get the approximate frequency, go back to your +frequency table and the closest thing to that will be the exact frequency. +it should sound like a series of weird beeps instead of static. remember that +frequency, it'll be important later. you don't need SDRSharp anymore. + +[qsg]: https://www.rtl-sdr.com/rtl-sdr-quick-start-guide/ +[RadioReference]: https://www.radioreference.com/apps/db/ + +## specific setup + +EDACS is a trunked system, so we're using [RTL-SDR's trunked radio tutorial][t] +as our guide, mostly. that guide assumes we have two RTL-SDRs, but there's a +piece at the end explaining how to do it with just one. that sucks. i'm going +to paraphrase it here. + +first, we're going to download the software we need: [Unitrunker][], +[VB-Cable][], and [DSD+][] (extract both the regular and DLL downloads to the +same folder). install unitrunker and VB-Cable and extract dsd+ somewhere +convenient. you might need to reboot after installing VB-Cable because +computers are bad. VB-Cable might set your default input and output devices to +the wrong things when you install it, so switch them back if it does. + +open up dsd+. it'll open four different windows, one of them should have a list +of audio input and output devices. check the number in the input list that goes +with CABLE Output - for me it's 3. pull up notepad and make a new file. since +my input was number 3, i'm typing + +``` +DSDPlus.exe -i3M +``` + +in that file: if yours is not 3, put whatever the correct number is for you +instead of 3. then, save the file, find your DSDPlus folder, make sure the type +is set to "All Files", and name the file `run.bat`. close dsd+, go to that +folder, and open that `run.bat` file you just created. it should pull up dsd+ +and if you're lucky it'll print + +``` +audio input device #3 (CABLE Output (VB-Audio Virtual ) initialized +``` + +or something like that. leave that open. + +open up unitrunker. click the `+` to add a new receiver, and click the RTL2832 +button to add your RTL-SDR. set your settings around like this: + + + +the most important things are the RTL Device, the sample rate (2.56 msps), and +the VCOs (2 VCOs). i do not know what a VCO is and i do not care enough to find +out. we should now have two VCO tabs next to our info tab. the first one needs +to look kinda like this: + + + +the important things are the Role being Signal, the Park frequency being the +control channel we found earlier (mine is 851.7625), and the Mute box being +checked. the second VCO should look kinda like this: + + + +the important things are the Role being Voice, the Deemphasis box being +unchecked, and the Digital Output being set to your CABLE Input. this means it +will connect up with dsd+ listening to our CABLE Output. + +press Play now; it should pull up a window with a Channels tab. the Channels +tab should look something like this: + + + +but the Frequency column will all be zeroes except for the control frequency we +found earlier. you'll need to copy over the rest of the frequencies manually +from the RadioReference site. press the stop button and the play button again, +and everything should in theory be working. ideally, the Call History tab will +be crowded and updating pretty frequently, and unitrunker will be passing +things along to dsd+ which will give us the audio we want. technically, this is +enough. + +[t]: https://www.rtl-sdr.com/rtl-sdr-tutorial-following-trunked-radio-unitrunker/ +[Unitrunker]: http://www.unitrunker.com/ +[VB-Cable]: http://www.vb-cable.com/ +[DSD+]: https://www.dsdplus.com/ + +## groups + +the thing, though, is we don't have context for any of this. for now, at least. +RadioReference should have a table or several of talkgroups - the "list all in +one table" button may come in handy - and we can use that information to figure +out who we're hearing, and have at least some control over who takes priority +if multiple people in different contexts are talking at once. + +find the main unitrunker window - it's titled "Universal Trunker" and if you +don't have it open just click the home button a bunch until it opens - and then +open the Systems tab and double-click the one that exists. open the Groups tab +in that window, and it should give you a massive list with columns for ID, +Label, and a bunch of stuff we don't care about right now. the ID matches up +with the DEC column in the RadioReference table, and the Label can be either +"Description" or "Alpha Tag" or something you make up yourself if you feel +creative. if you pay RadioReference $15 for a Premium subscription then +unitrunker can import that data automatically. + +once you've filled that all in, open the Sites tab and double-click the entry +you see there, then open the Call History tab. the group labels you added +should now be appearing in the Audience column; the LCN and Frequency should +turn green for what unitrunker is currently listening to. + +back in the Groups tab, you can edit the Priority values to control which +groups will be chosen more often - as far as i can tell, higher priority groups +will interrupt lower priority groups, and equal priority groups will just play +whoever started talking first. + +## broadcasting + +this setup lets you listen to things locally, but what if you want your +comrades with no hardware to be able to also listen? the laziest option is to +just stream the Call History window on Twitch or something, but in theory there +are better options. RadioReference runs Broadcastify, which is designed for +hosting police scanner livestreams, but they have to manually approve your +broadcast, which is annoying for short term activity. you could run an icecast +server yourself or something, but that takes effort to configure. honestly all +of those kinda suck but those are your options as far as i know. |