Tagged: 433

Using an RTL-SDR to help open a Gated Community

Tomasz lives in a gated community, but as he doesn’t own a car he wasn’t given access to a gate remote control. This made it difficult for him to have friends who have cars visit him. So he decided to use an RTL-SDR to receive, capture, analyze the gate signal which is transmitted at 433 MHz and then copy the signal to use with his own homemade transmitter.

First Tomasz used his RTL-SDR with SDR# to capture a few sound files of the gate remote which transmits at 433 MHz. Then he viewed the sound waveform’s in Audacity, a free audio editing program. Just by looking at the waveform he was able to determine that the signal was On-Off Key (OOK) modulated and that each frame of the transmission was the same, meaning that no security scheme was used.

Next he wrote down the transmission parameters that he learned from his analysis and built a simple 433 MHz transmitter which he connected to a microcontroller. After programming his microcontroller to send a copied signal he was able to open the gate.

433 MHz Gate Remote Received on the RTL-SDR
433 MHz Gate Remote Received on the RTL-SDR

Analyzing 433 MHz Transmitters with the RTL-SDR

Over on his blog, Yashin has written a post showing how to analyze 433 MHz transmitters using several methods. Devices that transmit using low power 433 MHz are common and often include devices such as weather monitors, power monitors and alarm sensors.

To show his analysis methods Yashin used an ASK modulated FS1000A 433 MHz transmitter connected to an Arduino Teensy microcontroller. He first uses GQRX and baudline together with an RTL-SDR in Kali Linux to test that the transmitter is working and to visually inspect the RF spectrum. Then he shows how to use GNU Radio to receive the 433 MHz transmitter and how to record an audio file. The final tool he shows how to use is rtl_433 which will automatically decode the data into binary strings using the analysis option.

ASK 433 MHz Transmitter
ASK 433 MHz Transmitter