What is FreeDV Mode in Amateur Radio?

| October 21, 2026 | Amateur Radio (Ham Radio) | No Comments

FreeDV is an open-source Digital Voice (DV) mode designed specifically for HF radio. Unlike proprietary VHF/UHF digital modes which require specialized hardware chips, FreeDV is entirely software-based and operates seamlessly within a standard Single Sideband (SSB) bandwidth. The FreeDV Project is managed by a team which includes VK5DGR, K6AQ, K5WH, K0PFX, G8SEZ, and VK3TPM.

It allows operators to transmit clear, noise-free voice communications over fading HF channels, often at lower Signal-to-Noise Ratios (SNR) than traditional analog SSB.

How It Works

At its core, FreeDV relies on two main components to squeeze human voice into a narrow HF channel:

  1. Codec 2: An open-source speech codec. It highly compresses analog speech down to extremely low bitrates (typically between 700 bps and 3200 bps) by modeling the human vocal tract rather than just digitizing audio waveforms.
  2. OFDM Modem: The compressed digital data is then modulated into multiple audio tones using Orthogonal Frequency-Division Multiplexing (OFDM).

When you transmit, these OFDM tones are fed into the microphone input (or line-in) of your SSB transceiver. The radio simply transmits these audio tones over the air as a standard SSB signal.

Why Use FreeDV?

  • No Static or Fading Noise: Because it is digital, you either hear clear voice or nothing at all. The constant, fatiguing hiss of HF background noise is completely eliminated.
  • Low SNR Performance: Advanced modes within the software (like the 700D mode) utilize Forward Error Correction (FEC) and can pull readable voice out of the noise floor at signal levels where analog SSB would be completely unintelligible.
  • Narrow Bandwidth: Depending on the mode selected, FreeDV signals can occupy as little as 1.25 kHz of bandwidth—about half of a standard SSB signal.

Station Setup

Setting up FreeDV is virtually identical to configuring a station for digital modes like FT8 or JTTY. For a station already routing audio via virtual cables (like VB-Audio or 710 Console) on a Linux or PC environment, no new hardware is required.

  • Audio In: Your microphone connects to the PC, where the FreeDV software compresses the speech.
  • Audio Out: The PC’s soundcard (or virtual cable) routes the OFDM audio tones to your transceiver’s audio input.
  • PTT Control: Triggered via CAT control or a standard COM port line.
  • Receive: The transceiver’s audio out feeds into the PC, where FreeDV demodulates the waterfall back into clear audio.

FreeDV frequencies

FreeDV operates over standard Single Sideband (SSB), relying on established global calling frequencies that serve as centers of activity rather than fixed, exclusive channels. Operators generally call “CQ FreeDV” on a primary frequency and then QSY (tune slightly up or down) to keep the initial frequency clear for others.

Global FreeDV Calling Frequencies

  • 160m: 1.870 MHz (Primary); 1.997 MHz (Alternate, Region 2)
  • 80m: 3.625 MHz (Primary); Alternates include 3.643, 3.693, 3.697, 3.803, and 3.850 MHz depending on your ITU Region
  • 60m: 5.3665, 5.3685, and 5.4035 MHz (Strictly subject to local and national regulations)
  • 40m: 7.177 MHz (Primary); 7.197 MHz (Alternate, Region 2)
  • 30m: No standardized calling frequencies
  • 20m: 14.236 MHz (Primary); 14.240 MHz (Alternate)
  • 17m: 18.118 MHz
  • 12m: 24.933 MHz
  • 10m: 28.330 MHz (Primary); 28.720 MHz (Alternate)
  • Satellites (QO-100): 2400.140 MHz (Uplink), 10489.640 MHz (Downlink)

Sideband Conventions

FreeDV strictly follows standard amateur radio SSB conventions based on the operating band:

  • 160m to 40m: Transmit using Lower Sideband (LSB).
  • 30m and above (including 20m, 17m, 12m, and 10m): Transmit using Upper Sideband (USB).
  • 60m: Generally requires USB, though this depends entirely on national band plans and specific channel allocations.

Operating Guidelines

  • Sub-band Compliance: Always verify that the selected frequency falls within the permitted phone (voice) or “all modes” segment of your local band plan.
  • QRM Avoidance: If a listed calling frequency is currently busy with analog SSB or other digital traffic, move 1 to 3 kHz away while ensuring you remain inside the appropriate sub-band.
  • Activity Days: The FreeDV community holds a global Activity Day on the third weekend of every month to boost worldwide contacts and coordinate testing.