pktfec-tnc is a software terminal node controller (TNC) for a new digimode meant to be transmitted over FM or NBFM channels. pktfec-tnc provides:

  • a low-density parity-check (LDPC) matrix for forward error correction (FEC),
  • puncturing to reduce overhead for messages that are not a multiple of the used block size,
  • an interleaver to reduce the impact of burst errors,
  • quadrature amplitude modulation (QAM) with a selectable number of bits per symbol (2, 4, 6, 8, ...) and smooth transition to limit audio bandwidth to frequencies between approximately 960 and 2880 Hz (1.9 kHz audio bandwidth to be transported over a 6 to 25 kHz wide FM channel),
  • net bitrates from 1200 bit/s (QPSK with 2 bits per symbol) up to 3600 bit/s (QAM64 with 6 bits per symbol) and more,
  • a TCP/IP server that supports multiple clients to receive and send messages via a simplified version of the KISS protocol (data frames only).


pktfec-tnc requires SoX (see for audio input and output.



  • 2019-02-15: Version alpha2
    • Some corrections in README file (including correct audio bandwidth)
    • Stricter synchronization requirement (reduce false positives)
    • Allow carrier frequency (baud-rate is half of carrier frequency) to be set on command-line of TNC
  • 2019-02-12: Initial release of version alpha1