Drop #158 (2022-12-17): Twelve Days of [Quick] Drops • Day 06
rtl_433 / Flipper Zero; rtl-sdr; 🛫🛬
On The Sixth Day Of Quick Drops 🎅🏽hrbrmstr🎅🏽 Gave To Me…
🎶 Radios A-Waving! 🎶
(If this is your first Xmas Quick Drop, head back to Day 01 to find out what's going on.)
O.K. The attempt to keep an “-ing” in this sixth drop day's tagline may be of mediocre quality. However, since a certain baby boy billionaire appears to be afraid of radio waves, I thought a focused drop on how one might get into the hobbyusiness of analyzing all those invisible waves around us might be useful. Especially so, as he's forced the takedown of a number of “how to” tweets regarding one particular use.
rtl_433 / Flipper Zero
Numerous types of signals are sent on specific radio frequency (RF) bands. Despite the specificity in the name, rtl_433 is a “generic data receiver, mainly for the 433.92 MHz, 868 MHz (SRD), 315 MHz, 345 MHz, and 915 MHz ISM bands.” Tons of devices operate on one or more of these frequencies, such as weather stations/sensors, garage doors, key fobs, and more.
If you're wondering where the "RTL" (sorry, "rtl") comes from, it's a prefix that Realtek uses for it's RF chipsets. You'll also see the acronym "SDR" in this space, which stands for software-defined radio, meaning software controls circuits in a piece of hardware that lets you capture and/or send signals on any radio frequency that chip supports, provided you have proper antennae, ofc.
I link to that page as the project is foundational to many other FOSS. It should be a good starting point to assist your efforts to become an RF mad scientist (I mean, I guess you could just be a “slightly annoyed”, or even “happy” scientist if you wish, I won't judge).
If all the C code and technobabble on that page (and in this general space) seems a bit daunting, drop some coin on a Flipper Zero and just start having fun. It's a “hacker's tamagotchi” that is 100% self-contained and ready to go at first boot, which can transmit/receive on these frequencies and has many built-in apps.
If something is made, it will be hacked.
“Hack” is a complex term that is most often (in the public sphere) meant to connote cybercrime activity. Hack/hackers/hacking is far more generic, and should really be associated with clever, curious humans who want to know how things work, then bend said things to their will.
DVB-T — “Digital Video Broadcasting — Terrestrial” — is a standard for the broadcast transmission of digital terrestrial television that dates back to 1997. DVB-T signals contain compressed digital audio, digital video and other data in an MPEG transport streams.
As tech got cheaper and smaller, companies started making cheap USB-enabled chipsets (a.k.a. dongles — WHO MAKES THESE NAMES UP?!) that one could attach an antenna to and tune in to these DVB-T signals. It turns out, that the way many of these chips are made makes it possible to take control of the horizontal and vertical (kind of literally] and peer (or shout) into this invisible wavy world.
Realtek RTL2832U were/are cheap and powerful versions of such chips. As such, they can be used as a cheap SDR (see previous section for the def), since the chip allows transferring the raw I/Q samples (see link in previous ❡) to the host. You do need to pair it with additional components to perform actual tuning (a.k.a. instructing it to work on a specific frequency). Luckily, you don't have to bust out your soldering gun, since all of this complex, oddly named bits come in shiny, pre-built USB packages.
This is a decent primer, which also has some of those pre-built USB packages (along with a starter antenna). You can get into this space for about a quarter of Benjamin.
That link also discusses RTL-SDR, so I'll leave you to their expert commentary.
I avoided mentioning ADS-B — Automatic Dependent Surveillance-Broadcast — in the header since what started this past week's twitter meltdown involved something that has been a thorn in the baby boy billionaire's side for years: folks tracking his private jets. All planes flying in the U.S. must be equipped with ADS-B to help with collision avoidance, finding lost/downed aircraft, and more. Personally, I’d be fine if planes of two specific rich individuals were lost forever.
You can head over to ADS-B Exchange yourself (you likely already have) to learn where to see current activity and lookup historical activity.
During the first two years of the pandemic, we setup a Raspberry Pi with a Flight Aware USB stick running. I wanted to track the quiescence and re-emergence of airplane activity (it was nice not having contrails in the sky and engine noise for a while). It's just a commercial wrapper on a tuner+RTL-chip combo (see previous section) that also comes with FOSS software which you can use to
track Musk's plane pretend you're an all-seeing aircraft overwatch.
Vox just did a deep dive on “The Twelve Days of Christmas” that seemed appropro to add to today's drop. ☮