Category Archives: SDR

RTL-SDR

OP25 Raspberry Pi Audio Sucks A Big DAC

Ok I’ve been on a roll playing with OP25 and Raspberry Pi and one thing I can tell you is that the onboard audio from the bcm2835 chip is somewhat inadequate.  Oh, it works but you’re going to need a powered speaker or really efficient headphones, and even then it is a bit light.

What to do?

Add a USB Digital to Analog converter (DAC).  Depicted here is a HiFiMeDIY USB DAC.  This is a tad bit expensive for this project but I have like 4 of these things laying around the house.  They are ridiculously good.   If you like music slap one of these bad boys on your laptop in the hotel room and the quality of your music will improve ten fold.

That’s not what we’re doing here though.

There are a LOT of USB DAC’s out there and some cost just a few dollars.  HiFiMeDIY makes some cheaper ones as well that are way more than enough for improving your OP25 sound.

 

 

The Phat DAC costs $15 but you’ll have to solder header pins on yourself.  That may be the cheapest, and best route.  It has the form factor for the Raspberry Pi Zero but it works on all the Pi’s.

 

 

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OP25 on a Raspberry Pi (part 3)

In my last part I set the Pi up to stream to Broadcastify.  In this one we are just going to pump audio out through the headphone jack.

I’m doing this with an old generic black RTL-SDR and it works and it works fine but it is kind of susceptible to heat and cold and the ppm correction drifts a bit.  I really recommend getting a v3 RTL-SDR or a NESDR Smart as they seem more stable.  At any rate it doesn’t matter, you’ll just have to deal with the drift if you have any.

My assumption here is that you have Raspbian installed on at least a Pi 3.  I haven’t tried it on a lesser Pi but I had it on a Pi 3 B + and then I found a couple Pi 3 B’s laying around and figured I’d reclaim my B+ for another project on another day.  OP25 runs fine on the Pi 3.

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OP25 Raspberry Pi Streaming Part 2

So I finally figured out OP25 and I have this brand new Raspberry Pi 3 B + laying around doing nothing.  In this segment we’ll install OP25 on Raspberry Pi and then take our police scanner feed and send it to the internet on Broadcastify.

As someone pointed out to me yesterday, “There’s an app for that” they are indeed correct.  You can get Police Scanner Apps for IOS and Android.   Guess where the feeds in those apps comes from?  If you said Broadcastify you’d be correct.  So if no one is feeding your municipality   then there will be no feed in the app.  We will be that feed.

So the assumption is that you have a Pi with Raspbian installed and you kind of know how to use it.

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OP25 For Dummies – Or how to build a police scanner for $30 (Part 1)

OP25 is a program that decodes P25 Phase 1 and Phase 2 digital radio.  Some municipal areas are upgrading to P25 Phase 2 so almost gone are the days that you can track them with a police scanner since P25 is a Trunked Radio system and not just a lone frequency to monitor.   The only things that do Phase 2 are hardware scanners and hardware radios and OP25 for software radios.  Bear in mind Phase 2 could be encrypted and nothing you can do will decode it.

OP25 is HARD.  I’m a geek and I messed with it on and off for a year or more and it whipped me more than once.  Now that I have it working I find that it is REMARKABLY easy and I’m mad at all the geeks out there who never made a simple tutorial.  There are tutorials out there, some good but everybody leaves out the good stuff or the stuff they took for granted.

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Othernet

We all know what the Internet is but what in the world is the Othernet?  (It used to be called Outernet).  The Othernet is unofficially dubbed “The Internet in Space” or “The Encyclopedia in Space” and it’s mission is to provide internet type information to the poor or to areas on earth which don’t have active internet.

I kind of view it as a back up to the internet and one more source of information in a SHTF scenario.  When the grid goes down as long as you have an othernet receiver and a generator or some batteries and a laptop the satellite in space will probably still be working fine.

The project is housed here.  Before you jump into the Othernet fire for the first time, know this. When you buy Othernet hardware, that’s all you get.  No manual, no instructions.  Nothing.  That being said one of the users over there made an amazing guide to setting up the Othernet.

If you start digging into this guy a bit he’s highly credentialed and you can better believe this hobbyist believes everything he has to say in this paper.  So it’s really all good.

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Your Short Wave Antenna And Rig Accessed From Anywhere

Do you want to listen to your Shortwave receiver at work?  Do you camp?  Do you travel and can’t carry a lot of gear with you?  If you did travel you can’t carry the gear with you to get the performance you get at home.   Here’s a way to access your short wave antenna via an RTL-SDR device.  You can’t really access your shortwave RADIO but you can get at your antenna.

You need an RTL-SDR device.

$30 gets you basically every radio frequency that you can imagine and there is no shortage of geeks out there to write software to listen to or decode or make use of all those radio signals. One really cool thing you can do is to set up a server which you can connect to from anywhere.

 

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The Sickness That is Short Wave Radio

I just took a little inventory of my short wave radios.  It shakes out like this:

  • Tecsun PL-660
  • Tecsun PL-880
  • Sangean ATS-909X
  • Kaito KA1103
  • Majestic El Cheapo Italian Radio
  • Tivdio V-115
  • C Crane SSB
  • Tecsun PL-365
  • Tecsun PL-380
  • Tecsun S2000
  • Tecsun PL-310ET
  • XHDATA D-808
  • Grundig Eton Satellit
Okay, you’re probably not reading this unless you are a Ham or an ShortWave Listener (SWL).  I probably seem like a rank amateur compared to many guys you’ve seen who have possibly dozens of more radios than I have.

Running an RTL_TCP Server Off Of A Router

An RTL_TCP server first of all is a taking a USB Software Defined Radio and setting it up as a server for receiving radio signals within the frequency parameters of the SDR device which can them be connected to from anywhere.  For example an RTL-SDR Version 3  operates from about 500 kHz (with direct sampling enabled) to about 1.7 GHz.

So if you set up the server you can be anywhere provided your server allows incoming connections to the internet or you can access your network via VPN, as I do, and connect back to it and hear all the local radio stations or radio signals that interest you.

What good is that?  Maybe there is a radio program you like but the station doesn’t stream.  Maybe you want to hear your kid playing his high school football game broadcast on local radio.  Maybe you set a microphone and transmitter up in your home as a security device (such as a baby monitor).  Maybe you want to listen to the local weather broadcast or maybe you are a scanner junkie and like hearing your local police scanner.  Whatever.  There are lots of reasons.

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Using A Laptop Without Internet

This is one of my favorite subjects.  Repurposing an older computer and using it when there is no available internet connection.  If you have internet that is a big plus and you can and should use it but computers are still pretty useful with no network with the addition of a couple of pieces of inexpensive hardware.

What can a computer do that isn’t hooked to the internet? Quite a lot actually. Here’s a few things you can do:

  • Watch digital over the air television
  • Listen to FM or AM radio
  • Listen to Shortwave Radio
  • Listen to Amateur Radio
  • Listen to emergency service transmissions such as police, fire, weather, etc.
  • Decode NOAA Weather Satellite Images
  • Detect Aircraft Overhead
  • Decode Digital Transmissions that are unencrypted

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