JT65, developed and released in late 2003, is intended for extremely weak but slowly varying signals, such as those found on troposcatter or Earth-Moon-Earth (EME, or "moonbounce") paths. It can decode signals many decibels below the noise floor, and can often allow amateurs to successfully exchange contact information without signals being audible to the human ear. Like the other modes, multiple-frequency shift keying is employed; unlike the other modes, messages are transmitted as atomic units after being compressed and then encoded with a process known as forward error correction (or "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 by the receiver. (The particular code used for JT65 is Reed-Solomon.) Because of this FEC process, messages are either decoded correctly or not decoded at all, with very high probability. After messages are encoded, they are transmitted using MFSK with 65 tones.
Operators have also begun using the JT65 mode for contacts on the HF bands, often using QRP (very low transmit power); while the mode was not originally intended for such use, its popularity has resulted in several new features being added to WSJT in order to facilitate HF operation. JT65-HF is shown in the image above.
There are a number of operating frequencies for JT65 on the HF bands. They are:
|10 meters||28076 kHz||Upper Sideband|
|12 meter||24917 kHz||Upper Sideband|
|15 meters||21076 kHz||Upper Sideband|
|17 meters||18102 kHz||Upper Sideband|
|20 meters||14076 kHz||Upper Sideband|
|30 meters||10139 kHz||Upper Sideband|
|40 meters||7076 kHz||Upper Sideband|
|80 meters||3576 kHz||Upper Sideband|
From the hflink.com website, they recommend the following guidelines for JT65 operation:
1. Operators should be careful of frequency selection, accurate clock, and calibration. Always listen and observe the waterfall spectrum of signals on the frequency before transmitting, and during activity.
2. JT65A is a weak signal digital QSO mode. Always use very low power on HF to avoid QRM to other JT65 signals and other modes. 20Watts ERP is maximum for normal activity and DXing in the 40metre to 10metre bands.
3. Normal activity of JT65A is in the "weak signal" part of the ham bands, near the PSK, MFSK, and Olivia 500 frequencies. JT65A should not be used in parts of the ham bands where faster digital modes are in use.
4. The long tone carrier duration of JT65 transmissions has potential to cause severe interference to other modes.
5. Do not use JT65 in 10144kHz-10150kHz because JT65A is NOT COMPATIBLE with MFSK, FSK, HELL, OLIVIA, CONTESTIA, ALE400, or RTTY and can cause severe interference to fast time-sharing modes such as PACKET, PACTOR, ALE, PSKmail, and APRS.
© 2019 , Jonathan Tucker N8MDP. All Rights Reserved.