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Comment by H8crilA | Hacker News Reader

Indeed, there is no stopping this in the current global aviation regime.

This might be a good opportunity to advertise ADS-B data collection: websites like flightradar24, flightaware, adsbexchange are powered by thousands of volunteers that collect and upload ADS-B radio transmissions broadcasted by aircraft. Most of the collection goes through an RTL-SDR dongle, so if you have a raspberry pi or some other machine that's up 24/7 - consider contributing! Minimal radio kit for signal reception (RTL-SDR+simple antenna) costs somewhere around USD50. It's also a good entry point for learning SDR and radio in general.

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There is the new Privacy ICAO Address (PIA) program [1] from the FAA that somewhat adds a layer of privacy. It's not perfect by any means, and you can piece together the data to figure out the actual identity if you're so inclined. However, it does provide a little bit of a buffer.

[1]: https://www.faa.gov/nextgen/equipadsb/privacy/

How do you join in? Is there a way to see if "your area" isn't well covered?

From adsbexchange FAQ (https://www.adsbexchange.com/faq/)

> Q: I live in XYZ, can you use another feeder there? Where can I see if you need more coverage in my area? Etc.

> A: The answer is simple. If you live on planet earth, yes, ADSBexchange.com could use a feeder at your location. The map may look like you see aircraft in your area, but the truth is you can’t see what you can’t see. To detect aircraft with MLAT, we need a minimum of 4 feeders to receive data and the more receivers see it the better the MLAT accuracy. If an aircraft is low altitude, feeders may have to be within a few miles.

I would also add what each individual site will not say explicitly: with a little bit of Linux configuration skills it's easy to upload to multiple aggregators at once.

https://flightaware.com/adsb/coverage/

You need a radio that can receive the ACARS frequencies, VHF around 130 MHz in the aviation band. It's a simple FSK over AM, like an old-school modem, so you just pipe your radio's audio into a software decoder. There are direct SDR approaches these days too. e.g. ADSB Exchange has a ready-to-go SD card image for Raspberry Pi if you have an SDR which can receive the relevant frequencies. https://www.adsbexchange.com/how-to-feed/

ACARS is something else, it's like SMS for aircraft. Also interesting data.

But this thread is about location: ADS-B (dependent broadcast) and to a lesser degree MLAT (secondary radar interrogation response), both of which primarily operate on 1090MHz.

With an unmodified RTL-SDR you can receive both, not at the same time and you'll want to swap antennas since the ranges are so different, but still :).

PS. The RTL-SDRs used for ADS-B often feature a modification: an analog filter centered at 1090MHz, which removes all other data but makes the 1090MHz reception better. You shouldn't have the filter if you want to play around on other frequencies with the same device.

Even if your area has coverage, adding radios increases resilience and may help triangulate the position of aircraft in other radio modes. You can also check the data yourself instead of depending on commercial sites, e.g. with tar1090.

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