JS8Call

What it is

JS8Call is a keyboard-to-keyboard mode built on FT8's weak-signal technology, but with the freedom FT8 lacks: you type your own text, in a conversation, to a specific station, and messages can be passed along. It is a way to keep chatting on a weak or noisy path where PSK31 or RTTY would fail.

What it adds to FT8

FT8 sends fixed messages in a rigid script. JS8Call borrows the same ingredients: tones that are heavily error-corrected and decoded below the noise, in timed slots. On top it breaks your text into small frames, one per slot, and adds the conventions of a conversation:

• Free text is split into frames, so an arbitrary sentence takes several slots.
• Directed messages address another operator, who can reply automatically with an acknowledgement.
• Relaying lets a station that hears both ends pass the message on, so a message can cross a gap that no single path covers.
• Stations can announce themselves with periodic heartbeats, so others know who is on.

The trade-off

The cost is time. Text is slow, because every message must be broken up and sent in slots. There are several speeds: slower ones are more sensitive, faster ones finish sooner, and both stations must use the same one. Expect a short sentence to take many seconds, not the instant feel of PSK31.

	FT8	JS8Call
Message	fixed script	free text
Conversation	exchange reports and sign off	open-ended
Relaying	no	yes
Speed	quickest contact	slower, deliberate

In practice

JS8Call suits low-power operating, camping and emergency-minded operators, since you can pass real information and use relays without internet. As with FT8, use USB, keep audio levels low, and run less than your rated power, because the transmitter is on for much of each slot. Check your computer's clock before you start.

Related

• FT8 and FT4Weak-signal 15-second and 7.5-second modes.
• PSK31Keyboard chat in 31 Hz.
• MFSK, Olivia and ContestiaRobust modes for poor conditions.
• Digital mode softwareWSJT-X, fldigi and friends.
• Winlink for emergenciesEmail when the internet is down.
• Digital modes overviewThe landscape of data modes and what each is for.