FT8 Mode

FT8 (Franke-Taylor design, 8-FSK modulation) is a digital mode created by Joe Taylor (K1JT, Nobel Prize-winning physicist) and Steve Franke (K9AN). Released in 2017, it has rapidly become the most popular digital mode on the HF bands. FT8 can decode signals far below the noise floor, enabling contacts that are impossible on voice or CW.

How FT8 Works

The Basics

• FT8 operates in 15-second transmit/receive cycles, synchronized to UTC.
• Messages are encoded using low-density parity-check (LDPC) forward error correction and transmitted using 8-tone frequency-shift keying (8-GFSK).
• Each transmission occupies approximately 50 Hz of bandwidth (compared to 2400 Hz for SSB voice).
• A single transmission carries a maximum of 77 bits of payload data -- enough for callsigns, grid squares, and signal reports, but not for freeform text.
• FT8 can decode signals as weak as -24 dB below the noise floor (SNR). For comparison, SSB voice needs roughly 0 dB or better.

Timing

FT8's 15-second cycle is strictly synchronized to UTC:

Second	Action
00	Sequence 1: Even stations transmit
15	Sequence 2: Odd stations transmit
30	Sequence 1: Even stations transmit
45	Sequence 2: Odd stations transmit

Your computer's clock must be accurate to within 1 second of UTC. Use NTP (Network Time Protocol) synchronization. On Windows, use a utility like Meinberg NTP or Dimension 4. On Linux and macOS, NTP is typically built into the OS.

The Standard QSO

An FT8 QSO follows a structured exchange:

Step	Transmitting Station	Message Content	Example
1	Station A calls CQ	CQ + callsign + grid	CQ W1ABC FN42
2	Station B responds	Callsign + callsign + grid	W1ABC W2XYZ FN31
3	Station A sends report	Callsign + callsign + report	W2XYZ W1ABC -12
4	Station B sends report	Callsign + callsign + R + report	W1ABC W2XYZ R-15
5	Station A confirms	Callsign + callsign + RR73	W2XYZ W1ABC RR73
6	Station B confirms	Callsign + callsign + 73	W1ABC W2XYZ 73

A complete QSO takes approximately 75--90 seconds (5--6 transmit cycles). The signal reports are in dB (e.g., -12 means the signal was decoded at 12 dB below the noise floor).

WSJT-X Software

WSJT-X is the primary software for FT8 operation. It is free, open-source, and available for Windows, macOS, and Linux.

Download: https://wsjt.sourceforge.io/wsjtx.html

Installation

1. Download the installer for your operating system.
2. Run the installer and follow the prompts.
3. Launch WSJT-X.

Initial Configuration

Go to File > Settings and configure the following tabs:

General Tab

• My Call: Enter your callsign
• My Grid: Enter your 6-character Maidenhead grid locator (e.g., FN42ab). Find yours at https://www.qrz.com/gridmapper
• Display: Choose your preferred display settings

Radio Tab

• Rig: Select your radio model from the dropdown. WSJT-X uses Hamlib for radio control.
• CAT Port: Select the serial port or network address for your radio's CAT (Computer-Aided Transceiver) control.
• Baud Rate / Data Bits / Stop Bits: Match your radio's CAT settings.
• PTT Method: How WSJT-X keys the transmitter:
  • CAT -- Uses the CAT connection to key PTT (most convenient)
  • VOX -- Radio's VOX circuit triggers PTT from audio
  • RTS/DTR -- Uses serial port lines for PTT

Audio Tab

• Input (Soundcard): Select the audio input device from your radio (either a dedicated sound card interface like the SignaLink, Digirig, or the radio's built-in USB audio).
• Output (Soundcard): Select the audio output device to your radio.

CRITICAL SETUP STEP

Do not over-drive the audio. FT8 requires clean, undistorted audio. Set your radio to USB mode (not FM) with a fixed bandwidth. Set the transmit audio level so that your radio's ALC meter shows zero or minimal ALC action. Excessive ALC compression destroys FT8 signals. Start with a very low audio output level from WSJT-X and increase slowly while watching the ALC meter.

Sound Card Interface Options

A sound card interface connects your computer's audio to your radio's microphone and speaker ports:

Interface	Price	Notes
Built-in USB audio	Free (if radio supports it)	Many modern radios (ICOM IC-7300, Yaesu FT-991A, etc.) have built-in USB sound cards and CAT control
Digirig	Budget	Compact, USB-C, supports CAT+Audio+PTT
SignaLink USB	Mid-range	Widely used, proven reliability
Tigertronics SignaLink	Mid-range	Long history of compatibility
RigBlaster	Mid-range	Multiple models for different setups
Homemrew	Varies	A simple transformer-isolated interface can be built for a few dollars

Operating FT8

Receiving

1. Set your radio to USB mode on the FT8 frequency for your band.
2. WSJT-X will display a waterfall showing signals in the passband and a decoded messages panel showing the text of decoded transmissions.
3. Decoded messages appear every 15 seconds after each receive period ends.

Standard FT8 Frequencies

Band	Dial Frequency (USB)
160m	1.840 MHz
80m	3.573 MHz
60m	5.357 MHz
40m	7.074 MHz
30m	10.136 MHz
20m	14.074 MHz
17m	18.100 MHz
15m	21.074 MHz
12m	24.915 MHz
10m	28.074 MHz
6m	50.313 MHz
2m	144.174 MHz

Set your radio's dial to the listed frequency. WSJT-X will display audio frequencies from 0--5000 Hz in the waterfall; FT8 signals typically appear between 200 and 3000 Hz.

Making a CQ Call

1. Select a clear spot on the waterfall (where no signals are present).
2. Set your TX frequency to that spot by holding Shift and clicking on the waterfall.
3. Check Enable Tx and select CQ from the message buttons.
4. WSJT-X will begin transmitting CQ at the start of the next appropriate time slot.
5. When a station responds, WSJT-X will automatically advance through the QSO sequence.
6. After the exchange is complete, the QSO is logged.

Responding to a CQ

1. Find a CQ call in the decoded messages panel.
2. Double-click on the CQ message. WSJT-X will automatically:
   • Set the TX frequency to the calling station's frequency (or your own frequency, depending on settings)
   • Load the correct response message
   • Begin transmitting at the appropriate time slot
3. If the calling station responds, WSJT-X advances through the QSO sequence automatically.

FT4 Mode

FT4 is a faster variant of FT8, designed for contest use:

• 7.5-second cycles (twice as fast as FT8)
• Slightly wider bandwidth (~80 Hz)
• Requires slightly stronger signals than FT8
• Used for rapid contest-style exchanges
• Available in WSJT-X alongside FT8

Logging and Integration

WSJT-X can:

• Log QSOs to its internal log file (ADIF format)
• Send logged QSOs to third-party logging software via UDP network packets (works with N1MM+, Log4OM, DXKeeper, etc.)
• Upload to PSK Reporter automatically, reporting what signals you decode (this helps the community map propagation)
• Export ADIF files for upload to LoTW, eQSL, and other services

Tips for FT8 Operating

1. Time synchronization is everything. If your clock is off by more than a second, you will not decode (or be decoded by) other stations. Verify your clock accuracy regularly.
2. Don't over-drive your transmitter. ALC action on digital modes creates splatter that interferes with adjacent signals. Keep ALC at zero.
3. Use split operation if your radio supports it. This allows your TX and RX frequencies to be different, which is essential when responding to CQ calls.
4. Watch your duty cycle. FT8 transmits at full power for 12.6 seconds out of every 15. This is nearly continuous duty. Reduce your power to about 50% of your radio's rated SSB power to avoid overheating the final amplifier.
5. Explore PSK Reporter (https://pskreporter.info) to see where your signal is being received. This is one of the best tools for understanding propagation in real time.
6. FT8 is not a "chat" mode. The structured exchange carries callsigns, grid squares, and signal reports -- nothing else. For keyboard-to-keyboard messaging with FT8-like performance, try JS8Call.
7. Be patient. During poor conditions, it may take several cycles for your CQ to be answered. Let the software work.

Contributors

IUU6

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