FST4SIM(1)

📦
version 3.0.2 · 14 versions
, in ubuntu stonking

💖 FST4SIM(1) — aka the WSJT-X manual page that's about to be your new hyperfixation 💖

okay so bestie, welcome to FST4SIM, one of the lil tools that ships with WSJT-X. she's a signal-simulator girlie. she makes fake-but-valid signals so you can test your setup before you go yelling into the actual ionosphere. iconic behaviour, honestly.

✨ NAME ✨

fst4sim, qra64sim — Generate simulated QRA64, FST4, and FST4W mode signals.

like. that's the whole vibe. she generates pretend signals. no cap. 🦋

🎀 SYNOPSIS 🎀

qra64sim msg A-E Nsigs fDop DT Nfiles SNR

fst4sim msg TRsec f0 DT h fDop del Nfiles SNR W

two whole personalities, one page. the qra64sim form and the fst4sim form. they do not take the same arguments, so don't mix them up, i'm begging 😭

🌸 DESCRIPTION 🌸

fst4sim can be used to generate FST4 and FST4W signals with user-specified message content, mode parameters, and SNR values.

that's it, that's the pitch. you pick the message, you pick the mode params, you pick the SNR — and she hands you back a .WAV you can play into your decoder. main character energy for your test bench fr fr 💅

🫶 ARGS 🫶

one bullet per argument, no skips, we don't gatekeep here:

  • msg — A valid QRA64, FST4, or FST4W message enclosed in quotation marks. yes the quotes matter. quote her or she won't parse, sorry 🎀
  • A-E — QRA64 sub-mode designator. like, a letter from A to E. that's the sub-mode, bestie.
  • Nsigs — Number of signals to simulate, distributed even across a 2000 Hz bandwidth. so they get spread out all nice and even over that 2000 Hz 💫
  • TRsec — A valid T/R period duration (s). seconds, girlie. the T/R period.
  • f0 — Integer signal frequency offset (Hz). int only, no decimals, don't try it 🙈
  • DT — Decimal signal time offset (s). this one's a decimal. seconds.
  • h — A valid modulation index.
  • fDop — Decimal Doppler frequency spread (Hz). decimal. Hz.
  • del — Decimal Watterson model delay (ms). decimal, but in milliseconds this time, watch out ⚠️
  • nfiles — Number of files to generate.
  • snr — Add Gaussian noise to simulate SNR in 2500 Hz bandwidth. yes she adds the noise for you. simulation girlie does everything 😌
  • W — Hint to break ties between ambiguous messages: 0 as 77-bit (FST4), 1 as 50-bit (FST4W).
k so real talk about the output files, because this part lowkey matters:

Generated files are 12000 Hz sample rate, 16-bit unsigned format, mono PCM .WAV files suitable for replay using WSJT-X either vie the GUI wsjtx(1) or using the command line slow mode decoder jt9(1). Files are named 000000_nnnnnn.wav (000000_nnnn.wav for QRA64), where nnnnnn or nnnn increments from zero.

so: 12 kHz, 16-bit unsigned, mono PCM .WAV. replay them through the wsjtx(1) GUI or through the command line slow mode decoder jt9(1). filenames go 000000_nnnnnn.wav — or 000000_nnnn.wav if it's QRA64 — and that nnnnnn/nnnn part just counts up from zero. slay 💜

👑 AUTHOR 👑

Joe Taylor, K1JT.

the legend himself. we stan. 🫡

📜 COPYING 📜

fcal is Copyright © 2001 - 2019 by Joseph H. Taylor, Jr., K1JT, with contributions from additional authors. WSJT-X is Open Source software, licensed under the GNU General Public License (GPLv3).

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

ok so the ALL CAPS bit is not me being dramatic (for once) — that's the actual warranty disclaimer and it's legally doing the heavy lifting. no warranty, bestie. she's free software and she's hoping to be useful, that's the deal 🤝

that's the whole page, you ate that 💅 this was FST4SIM(1), rendered from the WSJT-X manual, built with AsciiDoc 3.0.2-devel, dated 06/22/2026. go generate some fake signals and make them iconic ✨🦋🌸

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