HzDrop

Spectrum · audio inactive

Microphone

Not opened

Input level

—

Link

—

Packets

—

Screen lock

Inactive

Recording

Record input (20 s)

Protocol v8

One-way broadcast without acknowledgements. Coherent OFDM at 48 kHz: up to 320 carriers from 0.94 to 8.4 kHz (every 8th a pilot), 42.7 ms symbols plus an echo guard, QPSK or 16-QAM, 5G NR LDPC codes with soft decoding. The five modes were chosen from measurements between real devices: Contact for a speaker held on the microphone, Fast within about 20 cm facing each other, Normal within about 50 cm in any room, Far across a room even when the devices are not facing, Long Range, which puts all power into 1.0–3.3 kHz for the largest distance, and Silent, which moves the whole transmission (sync included) to 17.4–19.1 kHz where most adults cannot hear it — it needs a speaker and microphone that reach that high, and works best close up.

Files use a fountain code: any K packets rebuild K, in any order, so Send again or Repeat ×2/×3 add new packets instead of copies. Short messages are one codeword; every repeat adds new parity. A sync burst (chirp, two training symbols, descriptor) starts every ~3.5 s, so receivers can join late.