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Faster, More Contest-Friendly FT4 Digital Protocol to Debut in a Week


[UPDATED: 2019-04-24 @ 1818 UTC] A new, speedier, more contest-friendly digital mode is just days away, initially in beta form. WSJT-X developers say serious work on the new FT4 protocol began shortly after the FT8 Roundup held last December 1 – 2. The goal was a mode that could compete with RTTY contesting in terms of contact rates, while preserving many of the benefits of FT8.

“Over the past month a small group of volunteers have been conducting on-the-air tests of FT4,” the WSJT-X Development Group — Joe Taylor, K1JT; Steve Franke, K9AN; and Bill Somerville, G4WJ — announced this week. “The early tests were very successful and helped us to make a number of important design decisions. We believe FT4 has considerable promise for its intended purpose.”

The developers say FT-4 soon will be ready for testing by a larger group and they’re seeking interested participants who can offer their “considered feedback.” They suggest reading The FT4 Protocol for Digital Contesting first. A general release of the WSJT-X suite that includes FT4 is anticipated in July.

According to the document FT4 is an experimental digital mode designed specifically for radio contesting that — like FT8 — uses fixed-length transmissions, structured messages with formats optimized for minimal contacts, and strong forward-error correction. Transmit-receive sequences are 6 seconds, making it 2.5 times faster than FT8 and about the same speed as conventional RTTY for radio contesting. FT4 can work with signals 10 dB weaker what would be required to decode RTTY while using much less bandwidth.

Transmissions last for 4.48 seconds, compared to 12.64 seconds for FT8. Modulation uses four-tone frequency-shift keying at approximately 23.4 baud, with tones separated by the baud rate. The occupied bandwidth is 90 Hz.

“We plan to post downloadable installation packages for WSJT-X version 2.1.0-rc5 on Monday, April 29,” the Development Group said. The FT4 Protocol for Digital Contesting document includes:

  • Instructions for installing WSJT-X 2.1.0-rc5 and configuring FT4.

  • FT4 operating instructions.

  • A basic description of the FT4 protocol, modulation, and waveform.

  • Detailed sensitivity measurements for FT4 under a wide variety of simulated propagation conditions.

“A few parameters and operating behaviors of FT4 are still being tested and optimized,” the initial FT4 guide says. “It will be very useful to hold several more mock contest practice sessions, with a larger group of active participants.”

Even if these practice sessions reveal no serious bugs or inadequacies, the WSJT-X Development Group believes FT4 is still too new to be used in the ARRL VHF Contest (June 8 – 10) and ARRL Field Day (June 22 – 23). For that reason, release candidate WSJT-X 2.1.0-rc5 will “time out” on June 7.

Here is the proposed schedule related to the FT4 beta version rollout.

  • April 29: Second announcement, with links to downloadable installation packages for WSJT-X 2.1.0-rc5

  • May 9, 0000 – 0100 UTC: FT4 practice session, 7.090 MHz

  • May 14, 0000 – 0100 UTC: FT4 practice session, 7.090 MHz

  • June 5, 0000 – 0100 UTC: FT4 practice session, 7.090 MHz (if needed)

  • July 15: General Availability (GA) release of WSJT-X 2.1.0.




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