FreeDV is an open-source digital voice mode designed for use on the HF amateur radio bands. It replaces traditional analog SSB (Single Sideband voice with compressed digital audio, delivering clearer communication under weak-signal conditions.
nlike proprietary digital modes, FreeDV operates using freely available codecs like Codec2, making it an accessible and community-driven alternative for voice communication on HF.
How FreeDV Works
FreeDV works by digitizing your voice using the Codec2 audio codec, which compresses voice into low-bitrate data streams (700 to 2400 bits per second). These data streams are then transmitted over HF using a modem that encodes the digital signal into an audio waveform. On the receiving end, another FreeDV setup demodulates the audio signal and reconstructs the original speech.
The signal itself travels in a bandwidth similar to SSB (typically 1.1 to 1.6 kHz), meaning it can fit comfortably within traditional HF channels. Furthermore, because it uses modern error correction and modulation techniques, FreeDV maintains voice intelligibility even under noisy or fading band conditions.
Setting Up FreeDV with Your Radio
Getting started requires only a few components. You’ll need a Windows, Mac, or Linux computer with the software installed. Then, connect your HF transceiver to the computer via a sound card interface, such as a Signalink USB, RigBlaster, or similar. Some hams even use SDR transceivers and interface directly through virtual audio cables.
Once connected, configure the transmit and receive audio levels carefully. Most FreeDV users set the rig to USB mode. After that, select the appropriate FreeDV mode in the software (700D, 1600, 2020, etc.), and begin transmitting. It’s important to ensure your mic is disabled in the radio; instead, all audio input should come from the computer.
Advantages of Using FreeDV
One of FreeDV’s biggest strengths lies in its efficiency. Digital voice, especially using Codec2, can outperform analog SSB under weak signal conditions. Because the digital signal includes error correction, speech remains intelligible even when the signal is noisy or marginal. In many situations, FreeDV allows contacts that would otherwise be impossible using traditional analog voice.
Additionally, FreeDV is bandwidth-efficient. Its narrow footprint means it causes less adjacent channel interference and allows more signals to share a band. Moreover, since it’s open-source, it promotes innovation and transparency in digital radio technology—an important value for the amateur radio community.
Range and Propagation
The range of depends on HF propagation, transmitter power, antenna quality, and atmospheric conditions just like SSB. However, because the modes are more efficient, stations often report successful contacts at lower power levels or greater distances than they could manage with analog voice. For example, the 700D mode is optimized for weak signals and can often work where SSB fails.
Nevertheless, it still has susceptible to the same fading, noise, and QRM that affect all HF signals. That said, its resilience to these factors often gives it an edge, especially during low-signal conditions or when noise is high.
When and Where FreeDV is Usable
FreeDV shines in situations where bandwidth is limited, signals are weak, or operators want to experiment with cutting-edge digital technology. It’s ideal for long-distance (DX) contacts, especially during gray-line propagation or low solar activity. Operators also use it during HF contests, field day events, or for general ragchewing among digital enthusiasts.
Though not yet mainstream, FreeDV use is steadily growing. Enthusiasts around the world schedule contacts or conduct weekly nets using this mode. It can be a great tool for those who wish to explore HF digital voice while keeping their operations entirely open-source.
Calling Frequencies and Nets
Several calling frequencies are recognized by the FreeDV community. While these can vary by region, common frequencies include:
- 14.236 MHz – Most active frequency, especially for 20 meters
- 7.190 MHz – Popular for 40 meters
- 3.625 MHz – Used on 80 meters
- 21.313 MHz – Sometimes active on 15 meters
These are typically used in USB mode. However, activity varies depending on band conditions and operator presence. Some regions also have scheduled FreeDV nets. For example, weekend nets on 20 or 40 meters often include stations testing different FreeDV modes and firmware builds. Many operators coordinate skeds via online communities and reflectors.
Final Thoughts
FreeDV is a powerful tool that pushes the boundary of what’s possible with voice over HF. It provides better performance under poor conditions, encourages experimentation, and keeps digital voice in the hands of the ham community rather than locked in proprietary formats.
Although it requires a bit more setup than traditional SSB, the reward is a cleaner, more efficient voice mode that continues to gain traction as awareness grows.