JS8Call — HF Messaging and Off-Grid Communications
JS8Call is a weak-signal HF digital mode and messaging protocol derived from FT8 but designed for keyboard-to-keyboard conversation and store-and-forward messaging rather than rapid-fire contact exchange. Where FT8 is optimised for making brief logged contacts, JS8Call is designed for actual communication — sending messages, relaying traffic through other stations, and maintaining a network of stations that can pass information without any internet infrastructure. It has become particularly popular among EmComm operators, preppers, and anyone interested in off-grid digital communications.
JS8Call vs FT8
JS8Call uses the same underlying signal structure as FT8 — 8-tone FSK modulation with strong error correction — but extends the message length significantly. Where FT8 encodes a fixed 77-bit message (callsigns, grid square, signal report), JS8Call encodes free-form text messages up to several hundred characters. This allows actual conversation rather than the fixed exchange of FT8. JS8Call also offers multiple speed modes — Normal (15.6 WPM), Slow (8 WPM), Fast (25 WPM), Turbo (40 WPM), and Ultra — trading bandwidth for speed and sensitivity.
Store and forward messaging
JS8Call supports store-and-forward messaging through an @ALLCALL inbox system. A station can leave a message addressed to a specific callsign in the shared inbox. Any station that hears the message relays it, building a distributed message relay network. When the destination station comes on the air, nearby stations automatically deliver any stored messages. This creates a resilient messaging network that functions without internet infrastructure, central servers, or real-time contact — making it valuable for EmComm and off-grid scenarios where Winlink may not be available.
Download and install JS8Call
Download JS8Call free from js8call.com. The software runs on Windows, Mac, and Linux. Installation is straightforward. The interface is similar to WSJT-X if you have used FT8 — a waterfall display, decoded messages list, and a compose window for typing messages.
Configure your station
Enter your callsign and grid square in the settings. Configure your sound card interface or USB audio connection the same way as for WSJT-X. JS8Call uses the same audio connection approach as FT8 — radio audio in and out through a sound card interface or the radio's built-in USB audio. CAT control for automatic PTT is also supported with most modern radios.
Choose a frequency and mode
Tune to 14.078 MHz USB for 20m JS8Call or 7.078 MHz USB for 40m. Watch the waterfall for activity. JS8Call Normal mode is the best starting point. Enable automatic heartbeat transmission in the settings — your station will periodically announce its presence and grid square, building the distributed network awareness that makes store-and-forward messaging work.
Send your first message
Click on a decoded station in the activity window to start a directed message exchange. Type your message in the compose window and press Enter or the transmit button. JS8Call handles the encoding and timing automatically. For a general broadcast, use @ALLCALL as the destination to send a message that any receiving station can relay onward.
| Band | Frequency | Notes |
|---|---|---|
| 80m | 3.578 MHz | Regional at night — good for EmComm nets |
| 40m | 7.078 MHz | Most active JS8Call band — day and night |
| 30m | 10.130 MHz | CW/digital only band — less active |
| 20m | 14.078 MHz | Worldwide daytime coverage |
| 17m | 18.104 MHz | Less active — good for targeted contacts |
| 15m | 21.078 MHz | When band is open — good DX |
How is JS8Call different from Winlink?
Both provide HF digital messaging, but they work differently. Winlink uses a client-server model — your station connects to an RMS gateway node that bridges to the internet. JS8Call is fully peer-to-peer — messages travel directly between JS8Call stations without any central infrastructure, gateways, or internet connection required anywhere in the chain. JS8Call is slower and less structured than Winlink but has no dependency on maintained infrastructure.
Can JS8Call messages reach someone who is not on the air?
Yes — through the store-and-forward system. If station A sends a message to station B but B is not on the air, any JS8Call station that receives the message can store it and relay it later when B comes on line. The message propagates through the network until it reaches the destination. This is the key EmComm advantage — messages can be queued and delivered asynchronously without real-time contact.
What power do I need for JS8Call?
JS8Call inherits FT8's weak-signal capability — contacts are possible with 5–25W and a simple antenna. For EmComm use where reliable regional communications matter more than absolute weak-signal capability, 50–100W with a wire antenna is a solid starting point. The Normal mode balances sensitivity and speed for most applications.
Is JS8Call widely used?
JS8Call has a smaller user base than FT8 but a dedicated and growing community, particularly among EmComm operators, POTA activators who use it for check-ins, and off-grid communications enthusiasts. The PSKReporter and JS8Call map at pskreporter.info shows real-time global JS8Call activity. On 40m, there is typically activity around the clock.