Just a few weeks ago I got interested in this as well ("where does FR24 get its data from?"). I ended up buying a cheap RTL-SDR dongle (R820T2) and a small outdoor antenna. I run the free dump1090 tool (I'm on Fedora) to decode ADS-B messages, then my own simple "radar-like" visualization program ([1]) connects to dump1090's network socket to receive decoded data (SBS1 textual format). Even with the antenna just sitting in my room (on a photo tripod), I typically receive data from 10-20 aircraft, up to 190 km away. I drove to a hilltop this weekend (some 600 m higher) and immediately got >100 aircraft, up to 500 km.
The ADS-B Exchange situation is more complicated than it "was sold out," and there are valid reasons for not wanting to use them–but it is still the most comprehensive source of uncensored flight tracking data.
I share ADS-B data, how do I activate my free Business plan subscription?
Please sign up for a free Basic account using the following link using the same email address with which you registered your feed. Once your feed is live, your complimentary Business subscription will be activated.
I set one up a few months ago and was really surprised at how much coverage I got–I thought I might need an outdoor one, or at least to fiddle with it a bit, but even just plopped on my desk behind my computer screen on the ground floor of a three story house in a dense area I’m picking up planes from miles all around.
I built a little app that processes the data to count how many are flying low over the park nearby, so I can go there when it’s quiet: https://noisy.today/prospect-park/
Once you have a receiver, you can use a raspberry pi image like https://adsb.im/home to easily feed data to more than 20 different networks. FlightAware, FlightRadar24, ADS-B Exchange, airplanes.live, TheAirTraffic, etc. Most of the networks give extra privileges to people who feed them data.
They prioritize low-coverage areas (no idea how generous they are for covered areas).
Nearly all of their position data is from these receivers, so you're providing them with more coverage/redundancy for the plane positions.
The hardware is relatively cheap (under 50$) and I don't imagine the business tier costs them much money.
> I reckon if I shelled out for a business plan I could start doing some simple stuff with free tier / extra paid features
You don't need to they'll give it to you for free.
sidenote: You can build your own with an rtl-sdr and a raspberry pi/cheap computer. If you do this you can forward the data to all of the commercial sites for the free perks, and to all of the community sites.
Mine serves as a fun party trick. I never built this out but I always wanted to build a little display that shows the overhead plane's src/dest, speed, and altitude using the antenna.
https://www.adsbexchange.com/ways-to-join-the-exchange/