Hardware

This picks up captures from Aug 3-5 and Sep 24-25 on my RTL-SDR Blog V4 dongle; the first post has the full setup, the versions and how I chose the antenna’s element lengths. The short version of the setup: every capture used the dongle with the bias tee off and no external LNA or filter, on the Mac mini, with Homebrew’s librtlsdr 2.0.2 (the mainline library, not the RTL-SDR Blog fork) and rtl_433 25.12. I didn’t record where the antenna sat, how high, or which cable it used. The elements were 5.5 in for the runs on Aug 3-4, 2.5 in for the Aug 5 runs and 9.5 in for the Sep 24-25 runs; in between, on Aug 6-7, they were 16 in for the ship and aircraft tracking in the ships and aircraft post. The antenna was in a V shape until 08:45 on Aug 4 (runs M1, M2, D1 and D2) and straight vertical after that. Times are PDT (UTC-7) unless they say UTC; after 17:00 PDT the UTC date is the next day. ...

I’ve already written up two things I did with this $25 RTL-SDR Blog V4 dongle in San Francisco: three 433 MHz weather sensors and ships and aircraft over SF Bay. This post is the wider look at what’s on the air around me: the V4’s whole 500 kHz to 1.766 GHz range (datasheet), whether strong FM stations overload the receiver, and a 1560 kHz AM station that turned out to be an empty channel. ...

Rain attenuates radio signals, so in theory a TV antenna and a tuner that reports signal strength should make a rain gauge. A UHF broadcast at a fixed frequency should drop when precipitation is in the path between the transmitter and the antenna. Compare it against a VHF channel, which is much less affected by rain, and you can separate weather effects from transmitter issues. Same principle as dual-band GPS receivers canceling ionospheric delay by differencing L1 and L2. ...

After a few days of 433 MHz weather sensors, I pointed the same RTL-SDR Blog V4 ($25, secondhand off Craigslist) at San Francisco Bay: three long AIS runs for ships (they broadcast around 162 MHz) and one ADS-B run for aircraft (1090 MHz). I’m an electrical engineer but new to software-defined radio, so parts of this are me finding things out; outside knowledge is linked inline. Where I could, I compared what the software decoded with something outside my own capture, and every run’s date and time is in the table at the end so my numbers can be checked. ...

The Vornado fan remote project left me with an RTL-SDR Blog V4 ($25, secondhand off Craigslist) that had only ever looked at one fan’s 433 MHz remote. I used it for a survey of what’s on the air around me in San Francisco. The V4 covers 500 kHz to 1.766 GHz (datasheet), and I began with the rest of the 433 MHz band, where I could hear three weather sensors. This post covers Aug 3 and 4, 2026: an antenna-length calculation that turned out wrong, a sweep of the tuner gain, an eight-hour census of the band, and a weather sensor whose transmit clock drifts with its own temperature reading. ...

I bought a Vornado EOS 9 for the bedroom, a Wirecutter pick. It came with a remote, no protocol listed anywhere, no FCC ID that turned up anything useful. Flipper’s frequency analyzer put it near 433 MHz, and Read mode came back with no protocol match, which meant it wasn’t going to be one of the well-known families. (Read mode isn’t broken: pointed at my actual front-door bell, it decodes CAME 12bit at 315 MHz instantly, no histogram needed. The fan’s protocol is just genuinely unlisted.) So it was Read RAW and reverse engineering from scratch, or nothing. ...