As of this morning (August 20th I have the 43rd highest ranking of 130 in Ireland, 3rd highest Shannon uploader, and worldwide ranking of 6204 of 23,000, and going up by ~2000 positions a day at the moment.
I’m using a RaspberriPi 2b, an RTL-SDR dongle, and RTL-SDR 22dB LNA, and the antenna is a self-built colinear coaxial cable antenna with 8 116mm segments taped to the inside of an upstairs window. The software is dump1090 and the Flightradar24 uploader. I’m seeing ~850 aircraft a day, and an average daily max range of ~170 nautical miles (250km). Not bad for €50 or so of an outlay! I can see planes about 8000 feet above Dublin and 11,000 feet above Knock. The curvature of the earth combined with the lack of height of the antenna prevents me from seeing any lower.
The ADS-B signals are transmitted by every commercial aircraft and by most private aircraft, on a frequency of 1090 MHz. The information transmitted includes at least the ID of the plane and it’s current position and speed. When these signals are collected and processed, aggregator websites like Flightradar24 can show the current state of our aeronautical skies.
Improvements planned are the installation of an ADS-B specific filter/LNA from the RTL-SDR people that is en route. I did get one already but that failed within a few hours of installation so the warranty replacement was sought. That addition should mean that I have a bette chance of hearing planes through the house and increasing the range between my southeast and the west, as the window the antenna is in is facing to my northeast.
It is fairly interesting to see what is possible with some fairly basic items and a bit of DIY electronical knowledge!