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+---
+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:
+
+![one constant signal and a bunch of other signals coming in and out at other frequencies](/assets/2020-06-26-police-scanner-setup-1.png)
+
+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 RTL-SDR settings](/assets/2020-06-26-police-scanner-setup-2.png)
+
+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 RTL-SDR VCO 1 settings](/assets/2020-06-26-police-scanner-setup-3.png)
+
+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 RTL-SDR VCO 2 settings](/assets/2020-06-26-police-scanner-setup-4.png)
+
+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:
+
+![the unitrunker channels tab](/assets/2020-06-26-police-scanner-setup-5.png)
+
+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.