This little trek started when I found an old weather sensor in a drawer. These come with weather stations to show what the temperature is remotely (or wind speed, humidity or rainfall).
The specific FCC ID for my sensor is RNERF100MTX, sold by Chaney Instrument Co. under the ACURITE brand. I found a manual and learned that the device transmits in the ISM (Industrial, Scientific and Medical) band that spans 433.05 – 434.79 MHz. Weather sensors typically operate around 433.92 MHz, but the exact frequency can vary depending on the manufacturer and device.
I also learned from my research that such devices use simple off/on encoding. That’s why my original title, “Listening to the Weather,” had to be changed. I have a few devices that can receive the ISM band frequencies, but I selected an RTL-SDR dongle since there wasn’t going to be anything to listen to.
I’m all out of 17.3 cm half-wave dipole antennas. The closest I have is 14 cm, so that’s what I chose. The video that follows shows a tablet PC running SDRSharp. The sensor is lower right. The software is centered on 433.92 MHz, but the signals seem to be closer to 434.0 MHz. Every 16 seconds or so the LED on the sensor blinks and following that there is a burst of a signal on the display. What’s interesting is that there are other bursts on the display too. Those might correspond to other sensors (I have 3 in total).
Well, that was exciting — just kidding, but where there is a question, there may be someone with a passion to answer it, and that person may be Benjamin Larson, the developer of some public domain software, rtl_433. Its ReadMe file has a massive list of instruments that this software decodes; it even reads the TPMS sensors in your tires! It’s stand-alone, requiring just the software and the RTL-SDR.
I do my SDR listening on a Microsoft Surface 5th generation tablet running Windows 10, and so I downloaded the latest build for Windows: Release 25.02 for MSVC x64 systems. In case you want to try this, I’ll list the things I did wrong to perhaps save you some trouble; however, this is the end result in the form of a screenshot:
The horizontal lines divide transmissions. Channel refers to a setting on the sensors, A, B or C so that the weather station can tell them apart.
Oopies
I downloaded the latest release for 64-bit windows files from GitHub, specifically rtl_433-win-msvc-x64-25.02.zip. When extracted, there are several executable files. I picked the wrong one to work with my RTL_SDR dongle; the right one is rtl_433-rtlsdr.exe.
The second problem was a little tricker. When I ran the program, it displayed, “sdr_set_center_freq Failed to set center freq.” I wondered of this had something to do with the removal of the need to downscale frequencies in the V4 dongle. So I tried my old RTL_SDR V3 dongle and it worked perfectly. The command to get the results in the screenshot are:
rtl_433-rtlsdr -f 434M
The frequency on the SDRSharp display looked like 434, although the expected frequency was 433.92M. Both gave the same results.