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
1838 – 3576 – 7076 – 14076 – 10139 – 18102 – 21076 – 24920 – 28076
Best Resources about JT65A
Some interesting links from our JT65A operating mode links collection
NW7US
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
The complete Bozo's guide to JT65A by K3UK, learn how to install and operate WSJT software and start making QSO in weak signals operating modes
DL3VCO
An extension of the excellent decoding software JT65 HF by Joe W6CQZ for amateur radio digital mode JT65
JT65A Software
A selection from our JT65A Software links collection
K1JT
WSJT-X implements communication protocols including FST4, FST4W, FT4, FT8, JT4, JT9, JT65, Q65, MSK144, WSPR, and Echo. These modes facilitate reliable, confirmed QSOs under extreme weak-signal conditions. JT4, JT9, and JT65 utilize a nearly identical message structure and source encoding, employing timed **60-second** transmit/receive sequences synchronized with UTC. JT4 and JT65 are designed for
EME on VHF/UHF/microwave bands, while JT9 is optimized for MF and HF, offering **2 dB** greater sensitivity than JT65 with less than 10% of its bandwidth. Q65 provides submodes with varying T/R sequence lengths and tone spacings, suitable for
EME, ionospheric scatter, and weak signal operations on VHF, UHF, and microwave. FT4 and FT8 operate with T/R cycles of 7.5 and 15 seconds, respectively, supporting enhanced message formats for nonstandard callsigns and contest operations. MSK144 is engineered for Meteor Scatter on VHF bands. FST4 and FST4W target LF and MF bands, achieving fundamental sensitivities near theoretical limits for information throughput; FST4 is for two-way QSOs, and FST4W for quasi-beacon WSPR-style transmissions, without requiring the strict time synchronization of protocols like _EbNaut_. WSPR mode enables propagation path probing via low-power transmissions, incorporating programmable band-hopping. The **WSJT-X 2.7** General Availability release introduces the QMAP program, Q65 Pileup, SuperFox mode, a Hamlib update option, and a Message System. SuperFox mode transmits simultaneously to up to 9 Hounds with a constant envelope waveform, providing approximately +10 dB system gain compared to older Fox-and-Hound operations. _WSJT-X 2.7_ for _Windows_ platforms includes _MAP65 3.0_, a wideband polarization-matching tool for
EME. The **WSJT-X 3.0.0-rc1** candidate release represents a major revision with new features, some ported from _WSJT-X Improved_. This software is available for _Windows 7_ and later (32-bit/64-bit), various Linux distributions (Debian, Ubuntu, Fedora, RedHat, Raspberry Pi OS), and macOS (10.13 through 15). DXZone Focus: Weak Signal | Digital Modes | WSJT-X | Windows
F6CTE Patrick
Windows freeware multimode program by F6CTE it supports BPSK31 QPSK31 PSK63 PSK63F PSK10 PSKFEC31 PSKAM CW CCW THROB 4 bauds THROBX RTTY SITOR-AMTOR-NAVTEX FELD HELL PSK JT65 HELL HF FAX SSTV FILTERS
JT65A Videos
From our Youtube Channel
