RTL-SDR - what else we can do?

In the previous post, I showed how you can listen to traditional FM radio using an RTL-SDR dongle with SDR# software.

In general, it all comes down to the antenna you have. The RTL-SDR works great as a frequency scanner when paired with wideband antennas. But even with the stock kit antennas you can still pick up a few interesting signals.

Listening to PMR (walkie-talkie).

This is the simplest example to show how you can hear transmissions from another radio device using an RTL-SDR kit and the included antennas.

Step 1. Prepare walkie-talkie device.

Motorola T82 Extreme will be used as a transmitter. Let's set it to channel 1 with no subtones (CTCSS).

Step 2. Set up antenna. 

Channel 1in PMR has 446,00625 Mhz frequency. The wavelength is 0,672 m. So for our kit antenna (which is a half-wave dipole), we need to set each arm to one quarter of the wavelength - about 16,8 cm. 

To be precise, remember that the dipole base adds about 2 cm of metal length to each arm, so you should subtract those 2 cm from the calculated arm length - set each arm to about 14.8 cm:

Step 3. Set SDR# and start transmitting on PMR.

In order to receive PMR transmission do the following:

1. Manually set the 446,00625 MHz (channel 1 in PMR)
2. Set NFM for modulation and bandwidth filter 12,5 kHz.
3. Set squelch to 50 (because PMR is very close to antenna)
4. Set RF Gain to minimum (same reason - PMR very close to antenna)
5. Start transmitting on PMR.
6. Press play and You should hear the PMR:

Listening to weather station

Another interesting idea is capturing transmissions from wireless temperature/humidity sensors used in home weather stations. They operate at 433 MHz, but they’re far from the only devices using that band. You’ll also find it in things like car tire pressure sensors (TPMS) and garage/gate remote controls.

In SDR#, you can of course detect the RF transmission itself, but in this case you can do more than that: you can decode the transmission and display the information it contains.

Step 1: Prepare wireless sensor.

Step 2: Set up antenna.

The wavelength is 0,692 m. So for our kit antenna (which is a half-wave dipole), we need to set each arm to one quarter of the wavelength - about 17,3 cm. 

To be precise, remember that the dipole base adds about 2 cm of metal length to each arm, so you should subtract those 2 cm from the calculated arm length - set each arm to about 15,3 cm.

Step 3. Set SDR# - plugin

First we need a plugin for SDR# which "understands" the transmission on 433 MHz and knows how to decode it. You can download it from there: https://github.com/marco402/plugin-Rtl433-for-SdrSharp/tree/master/install. Just download a zip file which is correct for Your SDR# version. In my case, my SDR# i 32 bit, so I download file named last_x86.zip.

Then locate plugin directory under Your SDR# installation path. It should be folder named Plugins. Cteate a folder inside named RTL_433 and unpack content of last_x86.zip there. It will be 3 .dll files. Once done, It should look like this:

Step 4. SDR# - set up plugin

Open installed plugin by clicking on "hamburger" button, then Plugins, then RTL_433:

Then configure it:

Step 4: SDR# - listen and decode.

The order is important here. 

1. Press main play button in SDR#, 
2. Enable plugin by selecting checkbox in it. 
3. Press Start button in the plugin window (make sure frequency in plugin is set to 433 MHz). 
4. Main frequency in SDR# will be set to frequency selected in plugin:

When SDR# receives a transmission from the sensor, a pop-up window appears showing the received, decoded message. In this case, two windows popped up because I have two sensors: one outdoor sensor and one indoor sensor. We can see temperature and humidity, and some other technical information about the certain message in transmission.

RTL-SDR - radio waves on Your computer

One day I thought to myself that I’d like to listen to “classic” radio - the kind one where you dial in the frequency and adjust the antenna, not something streamed over the internet. And instead of using a traditional receiver (which I don’t own), I chose an RTL-SDR from that site: https://www.rtl-sdr.com/about-rtl-sdr/

I chose the kit that comes with antennas (https://www.rtl-sdr.com/buy-rtl-sdr-dvb-t-dongles/) and followed the software installation instructions (https://www.rtl-sdr.com/rtl-sdr-quick-start-guide/).

Below there is a step-by-step list of what you need to do to listen to traditional radio using your computer.

Installing software

Step 1. Go to https://airspy.com/download/ and download Software Defined Radio Package.

This is an application that will decode radio waves into sound. It's name is SDR# (SDRSharp). Please note that if You use top download button for downloading Software Defined Radio Package You will download 32-bit version of the software. This may be important if You plan to install additional plugins.

Step 2. Unpack downloaded .zip file to the desired location:

Step 3. As an administrator run the install-rtlsdr.bat. That script will download a driver for Your RTL-SDR dongle with a small application named Zadig which will be used to install that diver in Windows.

Step 4. First plug in Your RTL-SDR dongle in the USB then as an administrator run zadig.exe. Then make sure that below options are changed in Zadig:

• List all devices - make it checked
• Ignore Hubs or Composite Parents - make it unchecked

Step 5. Select proper device/interface in Zadig:

Make sure that proper device/interface is selected and WinUSB driver will be installed. Then press Install Driver:

Listening FM radio

Step 1. We will try to listen traditional FM radio (frequency range 88 - 108 MHz). Make sure Your RTL-SDR dongle is plugged into USB. Set the antenna included with the kit as a dipole with 70 cm per arm, and mount the whole thing vertically. Make sure that antenna is attached to RTL-SDR:

Step 2. Start SDR# using SDRSharp.dotnet8.exe. After start You have to select the RTL-SDR dongle to be used:

Step 3. Finally listening. 

You have to press play button, but when You press it without some changes in the software You will hear nothing. Here is what needs to be changed (marked red square):

1. Manually set the desired frequency.
2. Set NFM for bandwidth.
3. Make sure that Your RTL-SDR dongle is used as source
4. Most important: set RF Gain somewhere near the middle
5. Press Play button and enjoy: