JT65 is one of the weak-signal digital modes supported by WSJT, an application written in 2001 by Joseph Taylor K1JT, astrophysicist and Nobel Prize in Physics, and released as open source in 2005.
WSJT was initially developed for VHF communications and in particular mode for Meteor-Scatter and Moon-Bounce (EME). The particularity of this protocol is that permit to decode signals many decibels below the noise floor.
Like all other digital modes, it requires a PC with software, and a sound card interface but need the PC to be correctly in time sync because contacts with this mode need to be done in a very particular procedure.
QSO Procedure
Contact is done 60 seconds at a time. For 48 seconds, a station will transmit, and then there are 12 seconds of silence. During the next minute, the other station transmits again for 48 seconds, followed by 12 seconds of silence once more.
During the silence period, the software will decode received text and the receiving station can decide to answer a CQ, or reply to a call.
Protocol characteristics
During transmission messages are encoded and compressed with a process known as forward error correction (FEC). The FEC adds redundancy to the data, such that all of a message may be successfully recovered even if some bits are not received. This implies that messages are either decoded correctly or not decoded at all.
By working with JT65A you will notice that:
during each transmission the maximum number of characters can be sent is 13
messages are not displayed in real time but only at the decoding time frame.
Messages received are typically error-free
even with 1 watt you will be received by several stations
Common JT65A HF Frequencies
All frequencies (kHz) assume a transceiver display in USB mode
A very exaustive and complete article on JT65A and JT65-HF operating mode, including software download links, installation notes, how to make JT65A QSO and videos to correctly work with weak signals by NW7US
Facilitates reliable two-way communication under challenging propagation conditions, WSJT-X provides a suite of digital modes optimized for weak-signal operation across the amateur bands. These modes, including FT8, FT4, and Q65, are designed to decode signals significantly below the noise floor, enabling DX contacts, EME (Earth-Moon-Earth), and meteor scatter QSOs with modest station setups. The software supports various T/R sequence lengths and tone spacings, tailored for specific propagation phenomena and band characteristics, such as JT9 for MF/HF with **2 dB** greater sensitivity than JT65, and MSK144 for VHF meteor scatter. WSJT-X also integrates specialized tools like _MAP65_ for wideband EME reception with polarization matching to counter _Faraday rotation_, and QMAP for wideband Q65 reception with Earth-Moon-Earth Doppler correction. These companion programs extend the software's capabilities for advanced weak-signal work, particularly on VHF, UHF, and microwave frequencies. The project, maintained by Joe Taylor, K1JT, and the WSJT Development Team, is the official home and reference implementation for these weak-signal digital communication protocols. Recent releases, such as _WSJT-X 3.0.2_, introduce enhancements like the QMAP program, Q65 Pileup, and SuperFox mode, which offers approximately **+10 dB** system gain for Fox-and-Hound operations.
Download JT65-HF Amateur Radio software for reception/transmission of JT65A protocol with an emphasis upon its usage in the High Frequency Amateur Bands. This is the W6CQZ version not developed anymore.
