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.