JS8Call
| JS8Call | |
|---|---|
| Mode type | Digital keyboard-to-keyboard messaging, 8-tone frequency shift keying |
| Developed by | Jordan Sherer KN4CRD; now maintained by the JS8Call-Improved team |
| Origins | Begun in 2017 as FT8Call; renamed JS8Call in 2018 |
| Based on | The modulation and error-correcting code of FT8 |
| On the air | |
| Speeds | Slow, Normal, Fast and Turbo, now called JS8 40 (Normal uses 15-second periods) |
| Common frequencies | 7.078 MHz (40 m), 14.078 MHz (20 m) |
| Features | Directed messages, groups, store-and-forward, relaying, heartbeats |
| Needs | An SSB radio, a computer, a sound-card interface and accurate time |
JS8Call is a free program and digital mode for typed conversation and messaging, built on the weak-signal technology of FT8. FT8 messages are limited to call signs, grid squares, reports and a few characters of text, but JS8Call strings its transmissions together so that operators can send free-form text, and it adds features for reaching stations that are out of direct range. It was written by Jordan Sherer KN4CRD, who began it in 2017 as an experiment called FT8Call and renamed it JS8Call in 2018. Development has since passed to a volunteer group, the JS8Call-Improved team, which Sherer has joined; its releases again carry the JS8Call name, and version 3.0.3 came out in July 2026. It has a dedicated following among hams interested in emergency communications, low-power operating and conversation on poor bands.
How it works
JS8Call uses the same kind of signal as FT8: eight tones, a narrow bandwidth, strong error correction and fixed timed transmit periods, all of which let it decode signals well below the noise. Each transmission, or frame, carries only a few characters, so a longer message is split across several consecutive frames and reassembled by the receiving software. Text therefore arrives in bursts rather than letter by letter, and a sentence can take a minute or more to send. JS8Call is slow compared with PSK31 or RTTY, but it gets through when those modes cannot.
Operators can choose among several speeds. Normal, the default, uses 15-second periods like FT8. Slow uses longer periods and a narrower signal, for the weakest conditions, while Fast and Turbo (called JS8 40 in recent versions) use shorter periods and wider signals to move more text when signals are strong. Both stations must use the same speed.
As with FT8, the computer's clock must be accurate to within a second or two, so internet time synchronization or a GPS time source is needed.
Directed messages and groups
Much of JS8Call's traffic is directed: a transmission begins with the call sign of the intended recipient, and the software at the other end can answer simple queries automatically if its operator allows it. A station can ask another for a signal report, its grid square, its status or the list of stations it is hearing, all without the other operator at the keyboard.
Messages can also be sent to a group, written with an @ sign. @ALLCALL addresses every station that hears the transmission, and operators create their own groups, for a club, a net or an emergency team, which members add to their software. A message addressed to @APRSIS asks stations with an internet connection to pass it to the APRS network, for example to report a position.
Heartbeats, relays and store-and-forward
JS8Call is designed to work around gaps in coverage:
- A heartbeat is a short, optional automatic transmission saying, in effect, "I'm here and listening." Heartbeats are sent in a reserved part of the passband, and stations that hear them can reply with an acknowledgment, giving everyone a picture of who can hear whom.
- A relay passes a message through an intermediate station. If station A cannot hear station C but both can hear B, A can address the message to C by way of B, and B's software retransmits it.
- Store-and-forward lets a station hold a message in its inbox for a third station that is not on the air. When the recipient appears and asks for its messages, the waiting message is delivered.
Together these features make JS8Call a kind of slow, radio-only messaging network that works without the internet, which is why it appeals to emergency and preparedness groups. Because the software can answer, relay and store messages without an operator present, US operators should be familiar with the Part 97 rules on automatic control and remain responsible for what their stations transmit.
Getting started
Setting up JS8Call is much like setting up FT8: connect the radio's audio to the computer, configure radio control, enter a call sign and grid square, and set the radio to upper sideband on a JS8Call dial frequency, such as 7.078 MHz on 40 meters or 14.078 MHz on 20 meters. The program's frequency list includes the usual frequencies for each band. Watch the band activity window for a while to see who is on before calling CQ.