Three Horizon Insights applications require specialized hardware in order to receive radio transmissions. That is, they require Software Defined Radio (SDR) hardware.
SDR is a radio system where components typically implemented in analog hardware (e.g. mixers, filters, amplifiers, modulators/demodulators, detectors, etc.) are instead implemented by means of computer software.
Inexpensive SDR (US$25) has become possible because computer processing power has increased to a level where complex operations (e.g., Fast Fourier transforms) can be performed in real time in typical CPUs (or GPUs)
SDR was selected for Horizon Insights for advantages in:
Most of the team members developing these Horizon Insights selected the following device for development:
The NooElec NESDR antenna included with the SDR device is relatively low quality and general purpose. Dramatically better performance for a specific application (e.g., aircraft transponder listening) can be achieved with an antenna designed for a specific frequency band (and optionally filtered to pass through only that band). Also, any antenna will work better if not enclosed within a building. If you must have your antenna within a building it is best to locate the antenna near a window.
During our research we came across many interesting sources of information relevant to SDR. Here are some links we think you might find interesting for further learning.
RPi GPU FFT
FM, Speech to text
AIS Maritime Vessel Transponders
ADS-B Aircraft Transponders