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JS8Call is a weak-signal digital mode designed by Jordan Sherer (KN4CRD) that bridges the gap between FT8's extraordinary weak-signal performance and the freeform keyboard-to-keyboard communication of modes like PSK31. Built on the same WSJT-X modulation technology as FT8, JS8Call can decode signals deep in the noise — but instead of the rigid, automated exchanges of FT8, JS8Call lets you type actual messages and have real conversations.
JS8Call also introduces features that go beyond simple point-to-point communication: directed calling, group messaging, relay/store-and-forward networking, and heartbeat beacons that let you see who is active and reachable.
JS8Call and FT8 share the same underlying 8-GFSK modulation, but they serve fundamentally different purposes:
| Feature | FT8 | JS8Call |
|---|---|---|
| Purpose | Minimal contact exchange (callsigns + signal reports) | Keyboard-to-keyboard conversation and messaging |
| Message format | Fixed, structured (77-bit payload) | Freeform text, any content |
| Automation | Highly automated exchange | Operator-driven conversation |
| Networking | None (point-to-point) | Relay, store-and-forward, groups |
| Sensitivity | ~−24 dB SNR | ~−24 dB SNR (comparable) |
| Speed options | Fixed (15-second periods) | Multiple speeds (see below) |
Think of FT8 as a machine-to-machine protocol that happens to involve human operators, and JS8Call as a human-to-human communication system that happens to use the same radio technology.
You type whatever you want, and JS8Call transmits it character by character using the weak-signal modulation. Messages can be any length — the software breaks long messages into transmission-sized frames and reassembles them at the receiving end.
JS8Call offers multiple speed settings that trade speed for sensitivity:
You can change speed mid-conversation, and stations on different speed settings can coexist on the same band segment.
JS8Call supports several calling modes:
CQ calls — General calls, just like FT8 or any other mode.
Directed calls — Call a specific station by callsign. JS8Call handles the routing.
Group calls — Send messages addressed to a group name (like @APRN or @EMCOMM). Any station monitoring that group receives the message. This is useful for nets and topical discussions.
@ALLCALL — A broadcast to all listening stations.
JS8Call stations can transmit periodic heartbeat beacons — short automatic transmissions that announce the station's presence, grid square, and status. Other stations decode these beacons and maintain a list of active, reachable stations. This gives you a real-time picture of who is on the air and what paths are available, similar to how APRS works for position data.
One of JS8Call's most innovative features is its relay capability. If Station A cannot directly reach Station C, but both can reach Station B, JS8Call can automatically route the message through Station B. Station B's software handles the relay without operator intervention (if the operator has enabled relay mode).
This creates a mesh-like network where messages can hop through intermediate stations to reach their destination — a concept similar to packet radio digipeating but operating at weak-signal levels on HF.
JS8Call is free software available for Windows, macOS, and Linux, downloadable from the JS8Call website. It is a standalone application (not part of WSJT-X), though it shares WSJT-X's modulation codebase.
The hardware requirements are identical to FT8:
If you are already set up for FT8, you are ready for JS8Call with no additional hardware.
JS8Call's setup is similar to WSJT-X: enter your callsign and grid square, configure your radio and audio devices, and set your transmit power. JS8Call also lets you configure a station status message, heartbeat interval, and group memberships.
JS8Call has established calling frequencies on each band:
| Band | Dial frequency (MHz) |
|---|---|
| 80m | 3.578 |
| 40m | 7.078 |
| 30m | 10.130 |
| 20m | 14.078 |
| 15m | 21.078 |
| 10m | 28.078 |
JS8Call has gained particular interest in the emergency communications and preparedness communities because it combines weak-signal performance (long range, low power) with the ability to send actual messages — not just signal reports. Features like store-and-forward relay, group messaging, and heartbeat monitoring make it a practical tool for coordination when infrastructure is down.
The @EMCOMM group is monitored by many operators interested in emergency communications practice.