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SESK: Stuff Everyone Should Know · sesk.info/hame-jt65-eme

What was the JT65 digital mode originally designed for?

Moonbounce, also called EME.

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  1. Contesting on HF
  2. Sending SSTV pictures on 20 m
  3. EME (moonbounce) on VHF and higher bands ✔

Why: The WSJT-X guide says JT65 was designed for EME, meaning earth-moon-earth or moonbounce, on VHF and higher bands. Signals travel to the moon and reflect back.

Huh, didn't know that: WSJT-X lists the decode threshold as about minus 25 dB SNR for JT65, versus about minus 20 dB for FT8.

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How do you know when the moon has enough to eat? When it's full.
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References

Answer: EME (moonbounce) on VHF and higher bands. The WSJT-X guide says JT65 was designed for EME, meaning earth-moon-earth or moonbounce, on VHF and higher bands. Signals travel to the moon and reflect back.

  1. WSJT-X User Guide 2.7.0, Introduction wsjt.sourceforge.io/wsjtx-doc/wsjtx-main-2.7.0.html
    JT65 was designed for EME
    Checked 2026-10-11.
  2. WSJT-X User Guide 2.7.0 wsjt.sourceforge.io/wsjtx-doc/wsjtx-main-2.7.0.html
    Thresholds for decodability are around -20 dB for FT8
    Checked 2026-10-11.
  3. WSJT-X User Guide 2.7.0 wsjt.sourceforge.io/wsjtx-doc/wsjtx-main-2.7.0.html
    -25 dB for JT65
    Checked 2026-10-11.

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