GBPPR LOUDAUTO Experiments |
Capabilities
LOUDAUDO is an audio-based RF retro-reflector. It provides room audio from a targeted space using radar (PHOTOANLGO) and basic demodulation and audio post-processing.
LOUDAUTO's current design maximizes the gain of the Knowles EK/EY-series microphone. This makes it extremely useful for picking up room audio. It can pick up speech at a standard, office volume from over 20 feet away. Note that concealments may reduce this distance. It uses very little power, approximately 15 µA at 3.0 VDC. So little, in fact, that battery self-discharge (internal resistance) is more of an issue for serviceable lifetime than the power draw from this unit. The simplicity of the design allows the form factor to be tailored for specific operational requirements. All components are from Digi-Key, Mouser, or eBay, and so are non-attributable to GBPPR.
Concept of Operation
Room audio is picked up by the microphone and converted into an analog electrical signal. This signal is used to Pulse-Position Modulate (PPM) a square wave carrier signal running at around 100 kHz. This square wave is used to bias a Field Effect Transistor (FET) on-and-off. When a LOUDAUDIO unit is illuminated with a CW carrier from a nearby PHOTOANGLO radar unit, the illuminating signal is Amplitude Modulated (AM) with the PPM square wave. This signal is re-radiated (backscatter), where it is then picked up by the receive section of radar. It's then processed to recover the room audio. Processing is currently performed with a few dollars worth of parts because I'm not rich. LOUDAUTO is part of the ANGRYTAXPAYER family of radar retro-reflectors.

Pictures & Construction Notes
