HzDrop

Microphone input while listening; generated signal while sending. The chart runs only while this panel is open.

How it works

Chirps locate each packet. OFDM sends bytes on many tones using differential phase (DBPSK or DQPSK). Reed–Solomon repairs errors; CRC-16 checks the header and CRC-32 checks the payload.

Large transfers are sent and saved packet by packet, with no fixed transfer-size cap. Attached files are read in small slices, and received packets are saved in browser storage. Available storage limits how much you can receive. Text appears as it arrives, with a preview of the first 64KB; download the complete transfer for the full content.

Optional lossless gzip compression reduces airtime for compressible text and files. It is used only when the estimated transmission is shorter. The receiver decompresses data as it arrives; the final SHA-256 checks the complete transmitted stream. Both devices need this version for compressed transfers.

SHA-256 is calculated as packets arrive and checked against a final verification packet. A red receiver border marks a mismatch. There is no automatic packet recovery; resend the whole transfer if verification fails.

Each multi-packet transfer uses a control byte: its two lowest bits indicate 01 = more data follows, 10 = last data packet (SHA-256 follows), and 11 = SHA-256 verification packet; 00 is reserved. A separate start bit resets the receiver for a new transfer. Single-packet messages keep their original format without a control byte.

Microphone

Not opened

Input level

—

Screen lock

Inactive

Keep both devices close and their pages visible.