Category: Applications

Pranking Colleagues with the USRP B210 Software Defined Radio

The Ettus USRP B210 is an advanced $1,100 software defined radio that is capable of both transmit and receive. Balint, one of the researchers at Ettus, has posted a video showing how he was able to play a light hearted prank on some of his colleagues using the B210.

Earlier in the year we posted about how Oona Raisanen was able to use her RTL-SDR to receive and decode restaurant pagers (the wireless devices given out at some restaurants to notify you when your food is ready).

Balint used his USRP210 controlled by a mobile phone app to transmit a fake signal to his colleague’s pager, causing it to activate before his food was ready.

You Can Page Me Anytime – USRP B210 + GNU Radio (teaser)

Receiving Urban Drainage And Flood Control Weather Sensors

In Boulder, Colorado (and possibly other US cities) there is a radio based weather monitoring system known as ‘Urban Drainage and Flood Control’. This is a system that monitors rainfall and other weather information and transmits data using the ALERT protocol.

Over at, blogger cparker has posted how he was able to receive and decode the RF signals sent by these stations using an RTL-SDR. Using cparker was able to determine that these stations transmit at 169.5 MHz using frequency shift keying (FSK).

Using his RTL-SDR and GQRX, he made a recording of some of the weather station packets on that frequency. Next he used a command line utility called minimodem to convert the recorded packets into binary data. After looking up the protocol online, he was then able to understand the binary string and extract the station ID information from it. Cparker then went on to write code that would plot the received stations on a map by cross referencing the station ID with a website containing location information about these sensors. Finally, he managed to get the whole system running live on a Raspberry Pi.

Urban Drainage and Flood Control
Urban Drainage and Flood Control Sensor Station

Raspberry PiRate Radio FM Transmitter

In November last year we posted a story showing how a Raspberry Pi could be used to transmit a digital AFSK signal to an RTL-SDR or other radio simply by connecting a wire to a GPIO pin.

Now an reader has written in to let us know that this concept has also been used before to create a 1 – 250 MHz FM transmitter using the Raspberry Pi and a program called PiFM. It uses the same concept of connecting a wire antenna to one of the GPIO pins but modulates the frequency using hardware on the Rpi meant to generate spread spectrum clock signals. It is claimed that it can transmit up to 50m away.

Below we show an example YouTube video of the Raspberry Pi FM radio transmitting to an RTL-SDR running HDSDR.

PiFm & R820T & HDSDR

New RTL-SDR Android App: SDRWeather

A new RTL-SDR Android app called SDRWeather has appeared on the Google Play Market. The new app allows you to listen to weather radio and decode EAS (Emergency Alert System) alerts. The app will only work in the US and Canada. More information about the app and its open source code can be found at

This software along with a supported USB software defined radio turns your Android device to a portable weather radio.

Current Features:
* Listen to weather radio in the US/Canada.
* Decode EAS Alerts US/Canada
* Selectable Pre-defined Frequencies
* Alert Notifications
* Widget to display alerts
* Option to unmute audio when alert recieved
* FIPS and CLC Location Code Databases
* Event Code Database
* No internet connection required

Possible future features
* Switch to using rtl_tcp_andro
* Option to only show alerts if you are currently in the affected region
* Affected region map

Screenshot of the Android RTL-SDR App SDRWeather
Screenshot of the Android RTL-SDR App SDRWeather

GPS Tracking with a modified TCXO RTL-SDR

Michele from Michele’s GNSS blog has posted his results with using a modified R820T RTL-SDR with Temperature Controlled Oscillator (TCXO) for GPS reception and decoding. The RTL-SDR is capable of tracking GPS even without TCXO but improved performance can be expected with a more stable oscillator. He notes that the R820T with it’s 3.57 MHz IF is ideally suited for GPS reception when combined with an active GPS antenna. Using this setup he was able to track GPS satellites and the Galileo E1B/C GNSS satellites as well.

Michele modified his R820T RTL-SDR with a 28.8 MHz TCXO he obtained from a friend. It is however possible to purchase modified TCXO R820T dongles directly from the 1090mhz webstore.

Modified TCXO R820T RTL-SDR used for GPS reception.
Modified TCXO R820T RTL-SDR used for GPS reception.

Receiving the Chinese Space Station Tiangong-1 with the RTL-SDR

Blogger gat3way has created a post on his blog showing how he was able to receive the Chinese space station Tiangong-1 with the RTL-SDR and a simple cantenna antenna.

The Tiangong-1 station transmits a signal at 2232.15 MHz. To get this signal into a range receivable by the RTL-SDR gat3way used a LNB (Low Noise Block) to downconvert the frequency into one that the RTL-SDR can receive. Using this setup he was able to get a decent signal copy.

Cantenna setup for receiving the Tiangong-1 Chinese Space Station
Cantenna setup for receiving the Tiangong-1 Chinese Space Station

Receiving and Decoding Data from an Esophageal Monitor Inside the Body

Blogger Dolske has recently posted about how he was able to receive and decode signals coming from inside his body. The signals originated from a Bravo Ph Esophageal monitor which is a small wireless sensor that is attached inside your body by a doctor. It is used to monitor pH levels within the body to help diagnose esophageal problems such as acid reflux. The monitor remains in the body for a number of days continually sending data to an external monitoring device which records and logs the pH data.

Bravo pH Esophageal Monitor
Bravo pH Esophageal Monitor

Using his RTL-SDR, Dolse was able to capture the wireless monitors signal using information he found about the monitor online. He found that the monitor used amplitude-shift keying and transmitted at 433.92 MHz. After capturing some signals with the RTL-SDR, he looked at the captured waveform in Audacity and was able to decode a few packets by hand. Finally, he went even further and wrote a Firefox browser based decoder which decodes and displays the pH data on screen.

Web Interface for Showing Decoded pH data from the Esophageal monitor.
Web Interface for Showing Decoded pH data from the Esophageal monitor.

Receiving SO-50 Saudisat 1C with the RTL-SDR

Over on YouTube user Orlando Lima shows reception of the SO-50 Saudisat 1C satellite. Saudisat is an amateur radio satellite with an FM radio repeater. Orlando listened to the downlink frequency at 436.795 MHz using an RTL-SDR, Yagi antenna and Orbitron software to track the downlink frequency in SDR#.

Passagem do satélite SO-50 SAUDISAT 1C

Aircraft Messages with HFDL, MultiPSK and the RTL-SDR

Over on YouTube user k2nccvids has posted two videos showing how he was able to decode High Frequency Data Link (HFDL) packets using the RTL-SDR, Ham-it-up upconverterMultiPSK and HFDL Display. HFDL is a service similar to ACARS but sent over HF frequencies. It is used to sent short messages to and from aircraft and ground stations.

In the first video k2nccvids uses MultiPSK with the RTL-SDR directly and also uses the add on software HFDL Display to more clearly view received HFDL packets. In the second video he uses SDR-CONSOLEv2 to monitor three HFDL frequencies simultaneously, with MultiPSK and HFDL Display still being used for decoding and display.

Logic Trunked Radio Analyzer and the RTL-SDR

Over on YouTube user k2nccvids has posted a short video showing the Logic Trunked Radio (LTR) Analyzer software working with SDR# and the RTL-SDR. Logic Trunked Radio is a type of radio trunking system that uses distributed control channels modulated into the analogue voice channel instead of using just one signal control channel.

LTR Analyzer Sample