Here is a fun project that you can do that allows you to track airplanes in real time for less than $50.
USB RTL-SDR (hardware that can capture radio waves): http://www.amazon.com/NooElec-RTL-SDR-RTL2832U-Software-Packages/dp/B008S7AVTC
External Antenna Connector (optional as it includes a mini antenna with the above USB device): http://www.amazon.com/coaxial-cable-female-right-angle/dp/B00CKG6T9I/
Dump 1090 (software that logs the data and shows the planes in realtime on google maps): https://github.com/antirez/dump1090
10-15 Feet of Coax Cable (any scraps will do).
Collinear Antenna build with coax cable (optional):
Install your favorite version of Linux, Dump 1090. Plug in your USB hardware. Execute the following:
./dump1090 --interactive --net Finally open the browser and browse to http://localhost:8080 to see live traffic.