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Digital radio

Digital voice, video and packet modes

  • All modes tranmitted and received in simplex, duplex and semi-duplex mode
  • M17 digital voice modulator and demodulator
  • Full duplex DQPSK 250 kbit/s and 4FSK 100 kbit/s IP radio modems with configurable TX/RX offsets. Allows exchanging IP packets between two SDR systems.
  • Digital mode repeater - in full duplex mode only, same mode or mixed mode repeater (e.g. FM to Codec2 and viceversa, or FM to Opus and viceversa)
  • Digital voice codecs: Codec2 700 bit/s, Codec2 1400 bit/s, Opus 9400 bit/s
  • Digital voice modem bitrates over the air from 1 kbit/s to 10 kbit/s
  • FreeDV digital voice modulator and demodulator (currently supports only 1600, 700C, 700D and 800XA modes)
  • Simple, low resolution video mode (JPEG encoded) operating at 10 frames per second in 300 kHz bandwidth, with audio using the Opus codec at 9400 kbit/s
  • For digital voice modes, an audio compressor can be used to increase the voice readability

Digital modulation waveforms

M17 digital mode

M17 voice transmission, setting of channel access number, source callsign, destination callsign, destination type. The M17 transceiver uses code from OpenRTX but supports only the voice part of the M17 specification.

TX split

FreeDV 1600

Voice only transmission and reception.

TX split

FreeDV 700C and FreeDV 700D

Voice only transmission and reception.

TX split

FreeDV 800XA

Voice only transmission and reception.

TX split

BPSK 1ksps and BPSK 2ksps

Voice and text transmission and reception modes using both Codec2 700 and 1400 bit/s. The audio codec payload is protected with rate 1/2 convolutional code FEC.

TX split

DQPSK 1ksps, DQPSK 2 ksps, DQPSK 10 ksps, DQPSK 250 ksps

Voice and text transmission and reception modes using Codec2 700, 1400 bit/s and Opus 9400 bit/s. The audio codec payload is protected with rate 1/2 convolutional code FEC.

The DQPSK 250 ksps mode is also used to transmit low resolution video at a framerate of 10 frames/s. The video transmission also features audio using the Opus codec at 9400 bit/s.

The DQPSK 250 ksps mode can also be used as an IP data modem operating in full-duplex with a configurable separation between RX and TX.

TX split

2FSK 1 ksps, 2FSK 2 ksps, 2FSK 10 ksps, GMSK

Voice and text transmission and reception modes using Codec2 700 and 1400 bit/s modes, or Opus 9400 bit/s. The audio codec payload is protected with rate 1/2 convolutional code FEC.

There are two types of 2FSK modulators and demodulators: using root raised cosine filtering and frequency demodulation, and using matched filters.

TX split

4FSK 1 ksps, 4FSK 2 ksps, 4FSK 10 ksps, 4FSK 100 ksps

Voice and text transmission and reception modes using Codec2 700 and 1400 bit/s or Opus 9400 bit/s. The audio codec payload is protected with rate 1/2 convolutional code FEC.

There are two types of 4FSK modulators and demodulators: using root raised cosine filtering and frequency demodulation, and using matched filters.

The 4FSK 100 ksps mode with RRC filtering can be used as an IP data modem operating in full-duplex with a configurable separation between RX and TX.

TX split

DMR, M17, System Fusion, D-Star full duplex base station

  • MMDVM base station mode with TDMA support (DMR, System Fusion, D-Star, M17) using LimeSDR and Ettus USRP devices
  • ETSI compliant DMR base station (repeater) supporting double timeslot TDMA with LimeSDR and Ettus USRP family devices and MMDVM-SDR.
  • Multi-channel / multi-carrier MMDVM system using LimeSDR and Ettus USRP devices. Up to 7 carriers supported in 200 kHz bandwidth, duplex mode. Number of channels can be configured between 2 and 7. Channel separation configurable to 12.5 or 25 kHz.
  • DMR tier III trunked radio base station using LimeSDR and USRP devices. The trunked radio base station supports one control channel and up to six payload channels. Each payload channel uses the standard DMR air interface in TDMA mode with two timeslots. The overall system capacity is 13 simultaneous voice or packet data calls.