JT65 and JT9

JT65 and JT9 are digital communication modes specifically designed for very weak signal transmission in amateur radio. They were developed by Joe Taylor (K1JT), a Nobel Prize winning physicist, to enable radio contact under extremely difficult conditions such as very low signal levels or reflected signals (e.g. moon or meteor scatter).

 

JT65

JT65 features

  • Weak signal mode: The JT65 is renowned for its ability to decode signals as low as -28 dB below noise. This makes it ideal for weak and distant signals.
  • Transmission duration: A transmission cycle takes 60 seconds. 48 seconds are reserved for the actual transmission of the signal, while the remaining time is used for processing and decoding.
  • Error correction: JT65 uses strong error correction to ensure that even weak and noisy signals can be reliably decoded.
  • Transmission structure: The protocol is highly structured and consists of defined message formats. Typical messages include callsigns, signal reports and locators.
  • Bandwidth: The JT65 uses a bandwidth of approximately 177 Hz, making it a narrow band mode. This allows many transmitters to be used in a small frequency range.

 

Typical applications for JT65

  • Lunar Bounce (EME, Earth-Moon-Earth): JT65 is often used for EME communications because of its ability to decode weak signals reflected from the Moon.

  • Meteor scatter: JT65 can be used to communicate via signals reflected from meteor trails.

  • DX hunting: Radio amateurs use JT65 to reach distant stations in difficult propagation conditions.

 

JT9

JT9 is a further development of JT65, designed for even weaker signals and narrower bandwidths.

 

Features of JT9

  • Narrower bandwidth: JT9 uses a bandwidth of only about 15.6 Hz, making it significantly narrower than JT65. This allows more efficient use of the radio spectrum.
  • Weaker signals: JT9 can decode signals up to -31 dB below noise, making it even more sensitive to weak signals than JT65.
  • Transmission duration: JT9 also has a transmission cycle of 60 seconds, similar to JT65.
  • Error correction: JT9 uses error correction similar to JT65, which supports reliable decoding of weak signals.
  • Frequency accuracy: As JT9 has a narrower bandwidth, more precise frequency stability is required from the transmitter.

 

Typical use of JT9

  • Weak signal conditions on shortwave: JT9 is widely used on shortwave bands where its narrow bandwidth and high sensitivity make it particularly effective.
  • Long distance links: JT9 is suitable for long distance DX communications, especially in difficult propagation conditions.
  • Narrow band digital communications: JT9 is preferred when many stations need to communicate in a small space, as its narrow bandwidth allows dense use of the frequency spectrum.

 

Differences between JT65 and JT9

  1. Bandwidth: JT65 has a bandwidth of about 177 Hz, while JT9 only requires about 15.6 Hz. This makes JT9 narrower and more spectrally efficient.
  2. Sensitivity: JT9 can decode signals up to -31 dB below noise, while JT65 can decode up to -28 dB.
  3. Applications: Both modes are designed for weak signals, but JT9 is better for short waves due to its narrower bandwidth, while JT65 is preferred for EME and meteor scatter.
  4. Frequency accuracy: Due to the narrower bandwidth, JT9 requires more precise frequency control than JT65.

 

Similarities between JT65 and JT9

  • Both modes use strong error correction and fixed message formats that include call signs, signal reports and locators.
  • Transmission cycles are 60 seconds each, with most of the time reserved for actual transmission and a small amount for decoding.
  • They are implemented in the WSJT-X software, designed specifically for weak-signal amateur radio.

 

Conclusion

JT65 and JT9 are powerful digital modes that allow radio amateurs to make reliable radio contacts even in extremely weak signal conditions. While JT65 is particularly suitable for EME and meteor scatter due to its slightly wider bandwidth and lower frequency requirements, JT9's narrower bandwidth and higher sensitivity offer advantages for communication on shortwave bands and in particularly weak signal conditions.