It is not difficult to receive nearby AM aircraft transmissions in the VHF airband (118 – 136 MHz). The aircraft transmissions use a bandwidth of 8.33 kHz.
Dutch coastguard Do228
Since the ‘old fashioned’ modulation AM is used, a simple detector (e.g. Schottky diode) can demodulate the airband waves. The schematic below shows a simple receiver that enables you to receive (strong, nearby) AM transmissions. Not a lot selectivity, so you may receive more transmissions on various frequencies at the same time..
More info about this design:
http://techlib.com/electronics/aircraft.htm
I was intrigued by a similar design - using PNP transistors - a long time ago. It was
a design from the book “Jongensradio” from 1967. I never built it.
