What Is JS8Call? An Introduction to the Digital Mode
JS8Call is an experiment to test the feasibility of a digital mode with the robustness of FT8, combined with a messaging and network protocol layer for weak signal communication on HF, using a keyboard-to-keyboard style interface. Put simply, it takes the extraordinary weak-signal decoding ability that made FT8 famous and layers on top of it the ability to have actual, free-flowing conversations, send stored messages, and build distributed relay networks — all without any internet infrastructure required.
The Origins of JS8Call and Its Development by KN4CRD
JS8Call was created by Jordan Sherer (KN4CRD) and first released January 04, 2019. The road to that first release, however, started much earlier. The initial idea of using a modification to the FT8 protocol to support long-form QSOs was developed by Jordan, KN4CRD, and submitted to the WSJT-X mailing list in July 2017. After experimenting with modifications to WSJT-X and gathering feedback from a small group of dedicated testers, the project — originally called FT8Call — evolved into its own standalone application.
JS8Call is a derivative of the WSJT-X application, restructured and redesigned for keyboard-to-keyboard message passing. It is not supported by nor endorsed by the WSJT-X development group. While the WSJT-X group maintains copyright over the original work and code, JS8Call is a derivative work licensed under the terms of the GPLv3 license. The software has continued to evolve, with version 2.5.0 released in January 2026, renamed back to JS8Call from JS8Call-Improved.
How JS8Call Differs From FT8 and Other Digital Modes
FT8 transmits and receives only the bare essentials needed to make an amateur radio contact: exchange of callsigns, readability report, signal strength report, and "best regards" (73). Because only this information can be sent, FT8 is not a "conversation" mode. JS8Call shatters that limitation entirely.
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, JS8Call encodes free-form text messages up to several hundred characters. This difference defines everything about how the two modes are used in practice.
Why JS8Call Is Gaining Popularity in the Ham Radio Community
Designed for emergency communication, grid-down scenarios, off-grid expeditions, and everyday amateur radio messaging, JS8Call keeps operators connected even when band conditions are poor or power levels are minimal. JS8Call is used daily by operators involved in EMCOMM, preparedness networks, off-grid communication groups, and recreational HF digital operators who value reliability and resilience.
Beyond the practical applications, there is a strong social element. The JS8Call community is very welcoming and the developers are willing to listen to your input. This community-first attitude — combined with the mode's unique capabilities — explains why JS8Call continues to grow even as newer digital modes compete for operators' attention.
How JS8Call Works: The Technical Foundation
Understanding JS8 Encoding and Weak Signal Technology
A customized digital signal processing (DSP) 8-frequency shift keying (8-FSK) FT8 modulation scheme is used; technically it's 8-audio FSK (8-AFSK) because shifts are generated using soundcard audio tones. There is a base radio frequency transport method (carrier) for any radio data, then a directed calling protocol is added supporting both free-form and directed messaging and relaying.
JS8Call integrates tightly with WSJT-X base libraries, inheriting robust forward-error correction and eight-tone FSK characteristics that decode signals buried deep in the noise floor. This inheritance from WSJT-X gives JS8Call its impressive weak-signal performance as a baseline, before its messaging and networking features are even considered.
Message Structure and Free-Text Communication
JS8Call turns FT8 into a "chat" mode, allowing stations to send longer messages keyboard-to-keyboard. JS8Call can be thought of like a very weak-signal radio broadcast form of email (though it is not email), where operators can check their message inbox and reply later. Messages can also be sent out to be relayed through other operators to reach a recipient operator. JS8Call conversations can also be had in real-time.
The directed messaging system is powerful. Directed messaging allows three commands to be used for message storage and retrieval at intermediate stations: MSG TO: [CALLSIGN] [MESSAGE] to store a message at an intermediate station; QUERY MSGS to query the destination for messages stored for your station callsign; and QUERY MSG [ID] to query for a specific stored message.
Bandwidth, Speed Modes: Normal, Slow, Fast, and Turbo
One of JS8Call's most practical features is its range of transmission speed modes, each trading bandwidth for sensitivity or speed. The four main speeds and their properties are: Slow — 30-second frames, 25 Hz bandwidth, around 8 WPM, decoded down to -28 dB; Normal — 15-second frames, 50 Hz bandwidth, around 16 WPM, decoded down to -24 dB; Fast — 10-second frames, 80 Hz bandwidth, around 24 WPM, decoded down to -20 dB; and Turbo — 6-second frames, 160 Hz bandwidth, around 40 WPM, decoded down to -18 dB.
The intent of the faster speeds is to start your QSO in Normal mode and "upgrade" to the faster speeds if conditions support it. Unless you have a weak computer with a slow CPU, you should enable MULTI from the mode menu, asking the decoder to decode all modes at once. This gives you maximum flexibility without having to guess what speed another station is using.
Signal-to-Noise Ratio and Propagation Advantages
JS8Call is considered one of the most important weak-signal digital modes due to its narrow bandwidth and robust weak-signal decode that can decode at -24 dB in Normal mode. JS8Call communication is slow but is often the only way to communicate when propagation is bad, noise is high, or both. This makes it uniquely valuable during challenging band conditions when other modes have already given up.
Running just 5–7 watts output, operators have reported being able to conduct a 2600-mile QSO in Slow mode because of the extra sensitivity the mode provides. That performance level rivals or exceeds what FT8 can achieve at the same power level, while still allowing a complete, meaningful conversation.
Getting Started with JS8Call: Software and Hardware Requirements
Downloading and Installing the JS8Call Software
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.
The main window is split into the Band Activity pane showing messages you have decoded, an Incoming Message Activity pane, a Call Activity pane showing the list of callsigns you have heard, a Message box where you enter your outgoing messages, and the Waterfall at the bottom giving you a visual indication of where the signals are in the passband. The learning curve for anyone who has used WSJT-X or any similar digital mode application is minimal.
Compatible Radios and Transceivers for JS8Call
The software works with any HF radio capable of USB digital audio, including Icom, Yaesu, Kenwood, Elecraft, Xiegu, and many others. Ongoing development ensures expanding compatibility, improved CAT control, and better integration with popular hardware. Virtually any modern HF transceiver capable of SSB operation can run JS8Call effectively.
JS8Call was designed to be lightweight and robust. It has very modest requirements and runs quite comfortably on a Raspberry Pi. This low hardware requirement makes it ideal for portable, battery-powered, and emergency go-kit deployments where you cannot afford to carry heavy laptop hardware.
Audio Interface Options: SignaLink, RigBlaster, and Built-In Sound Cards
The critical link between the radio and the computer is the audio interface. This may be an external sound-card interface, or a radio with a built-in USB audio codec. It carries receive and transmit audio in both directions and, in many cases, also provides push-to-talk control and CAT connectivity.
A good interface provides clean, isolated audio in both directions and dependable control of transmit and frequency. This reduces setup issues, avoids ground loops and RF feedback, and makes day-to-day operation far more predictable. Popular external interface options include the Tigertronics SignaLink USB and the West Mountain Radio RigBlaster series. Many modern radios from Icom, Yaesu, and Kenwood offer built-in USB audio and CAT control that eliminate the need for an external interface entirely.
CAT Control and Rig Integration Setup
CAT control, short for Computer Aided Transceiver control, allows the software to communicate directly with the radio. With CAT enabled, the software can read and set frequency, select the correct mode or data setting, trigger transmit without additional control lines, and log QSOs with accurate band and frequency information.
Operators configure the transceiver through straightforward CAT or OmniRig commands, set audio offsets within the 2 kHz passband, and may enable rig-control macros for split or automatic band switching, while an embedded Python scripting layer invites advanced automation such as scheduled beacons or remote telemetry forwarding.
JS8Call Frequencies and Band Plans
Standard JS8Call Frequencies Across HF Bands
JS8Call is designed as an HF mode covering 3–30 MHz, but as with any amateur radio mode, can also be used on VHF/UHF if desired. The standard calling frequencies are built into the software as defaults, making it easy to find activity right out of the box.
The most commonly used JS8Call frequencies across HF bands are:
- 160 meters: 1.843.5 MHz (USB)
- 80 meters: 3.578 MHz (USB)
- 60 meters: 5.363 MHz (USB)
- 40 meters: 7.078 MHz (USB)
- 30 meters: 10.130 MHz (USB)
- 20 meters: 14.078 MHz (USB)
- 17 meters: 18.104 MHz (USB)
- 15 meters: 21.078 MHz (USB)
- 10 meters: 28.078 MHz (USB)
These default calling frequencies are set up in JS8Call but are not set in stone and can easily be changed in your settings, or you can simply manually retune your radio to another frequency.
40 Meters, 20 Meters, and 80 Meters Activity Windows
JS8Call QSOs and other communications happen on 20 meters during the day at 14.078 MHz and on 40 meters at night at 7.078 MHz. These two bands represent the highest activity windows globally and are the best place to start when first getting on the air with JS8Call.
JS8Call is most active on 40 meters both day and night. You're likely to find stations less active on other bands, although 20 meters has more operators than it used to. For NVIS (Near Vertical Incidence Skywave) regional communications, 80 meters at night and 40 meters during the day are particularly valuable, especially for EmComm applications covering a region within a few hundred miles.
FCC Part 97 Regulations and Legal Operation of JS8Call
JS8Call is a fully legal digital mode under FCC Part 97 regulations. It falls under the category of data emissions and is permitted in the HF data sub-bands where other digital modes like FT8, PSK31, and Winlink operate. You must be a licensed amateur radio operator to transmit with JS8Call. A Technician license provides very limited HF privileges; a General or Extra class license provides full access to the HF bands where JS8Call activity is concentrated.
One important regulatory note: because some countries' amateur radio regulations prohibit unattended, automatic transceive operations where a control operator must always be present, JS8Call's default Behaviour > Idle Timeout is set to 60 minutes. If there is no keyboard input or mouse movement detected before the idle timer expires, the AUTO (transmit) mode is automatically turned off and your station operates in receive-only mode. Always operate in compliance with your national
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