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RTL_433 Data Decoding

The motivation

There are lots of low power, license free data transmitters on the 70cms (433 MHz) band. A large number of these are personal weather station sensors - others are tire pressure gauges in car wheels, wireless door bells and car remote locking systems.

I have a couple of cheap remote temperature sensors located in the garden - they feed data back to a clock (the kit was in an end of line sale from Maplin Electronics in the UK). Looking inside them reveled a 433 MHz SAW oscillator block.

I was interested to see if I could receive these sensors, and any others in the local area with a RTL SDR dongle.

The software

I did some experiments with recording a bunch of signals in the band (around 433.820 MHz +/- 30 KHz - the oscillators are not very accurate). Looking at the audio recording in baudline and audacity revealed obvious data bits, but decoding the signals by eye wasn't much fun. Then I found RTL_433, some software that automatically decodes many data transmissions off-air directly with an RTL Dongle.