Foundations of Amateur Radio

The other day a friend of mine mentioned in passing that they'd hooked their Home Assistant dashboard to an RTL-SDR dongle to listen to the various ISM bands. If that sounds like gibberish, let me elaborate.

"Home Assistant" is a tool that, among other things, allows you to control devices throughout your house, think lights, vacuum cleaner, air conditioning, and power sockets. It turns out that there are various plug-ins that allow you to connect it to a tool called "rtl_433", more on that in a moment.

ISM, or Industrial Scientific and Medical, is a global collection of 13 radio bands, regulated by the ITU, the International Telecommunications Union, where devices are permitted to transmit all different types of signals, think microwave ovens, NFC, or Near Field Communications, Wi-Fi, Bluetooth, but also weather stations, security devices, battery monitors, tyre pressure monitors, remote keyless entry, garage door openers and plenty more. The most "well known" ISM band is 433 MHz, but the most used ones are those we think of as Wi-Fi bands, 2.4 and 5.8 GHz. It sometimes comes as a surprise that Bluetooth and Wi-Fi share the same frequencies with each other and many different bits of technology.

While I'm here, I'll also point out that there are ISM allocations within the HF bands and up to 245 GHz, so plenty of spectrum to explore.

A different friend heard about my challenges with two remote controls, came by for a coffee and dropped off a frequency counter and left me to determine what type of remotes I had in my hands, since labelling was absent. After charging this sparkly new gadget I spent a while trying to make it do the needful, but ultimately, despite trying in multiple locations without local interference was unsuccessful, this likely caused by the nincompoop behind the controls, but I digress.

It occurred to me that an RTL-SDR dongle is perfectly suited to the job, as long as I can scan through the various frequencies and discover just which ones were associated with my cantankerous remotes.

As is my want, I got distracted by installing "rtl_433". I have to tell you, just plugging in an antenna into an RTL-SDR dongle, I'm currently using my 2m and 70cm dual band antenna, running the tool and looking at the log, in the last half hour alone, I've seen 372 reports, across 16 devices, including several cars and a truck, weather stations, security devices and plenty more; half an hour later we're up to 22 devices and 771 reports, and 24 hours in we're up to 128 devices, nearing 17,000 reports. I'll note that this is using an RTL-SDR dongle, no fancy radio, no filtering, no interference rejection, all straight from the device.

As you might expect, the reports keep trickling in, every 15 seconds or so there's a new decode and at this point I'm pretty sure I don't need to invest in a weather station in the near future, and if I figure out which Hyundai is driving around with low tyre pressure, I'll let them know.

Also, because I'm not just lollygagging, my remotes don't appear to emit anything that rtl_433 can decode, but I did notice that the reports stopped coming in while the remote was active, so I suppose that's progress.

In-case you're wondering, within "Fifty Things you can do with a Software Defined Radio", this is number "11: Read your neighbors'[sic] sensors".

At this point I hear the calls from the peanut gallery: "But .. but .. but, this isn't amateur radio" .. to which I say, "Really?"

In other words, amateur radio is what you make it and right now I'm interested in figuring out why my remotes are acting up and what better way than to play with radio, at whatever frequency takes my fancy.

I wonder if there's any HF gadgets I can monitor.

I'm Onno VK6FLAB