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, and Long Range, which puts all power into 1.0–3.3 kHz for the largest distance.

Files use a fountain code: any K packets rebuild K, in any order, so Send again or Repeat ×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.