Tuesday, October 09, 2007

Two new DigiModes: JT2 & JT4

Riprendo qui una notizia pubblicata dal SouthGate ARC:

Two new digital modes JT2 and JT4 are supported by an experimental version of the popular WSJT weak signal software.

JT2 has a bandwidth of just 8.75 Hz enabling dozens of contacts to take place in a 2.4 kHz SSB filter bandwidth.

WSJT version 5.9.8, r558 is the experimental release that contains the two new operating modes, JT2 and JT4.

JT2 uses 2-tone FSK modulation for synchronization and differential BPSK for the encoded user information. In this way both a sync bit and a data bit can be transmitted with each channel symbol. Symbols are sent at a rate of 4.375
baud, and tone separation for the 2-FSK modulation is 4.375 Hz.

JT4 uses 4-tone FSK, so it can also also include both a sync bit and a data bit in each symbol. Again the keying rate is 4.375 baud, and a number of different tone spacings are offered.

JT2 and JT4 are both designed for making QSOs under extremely weak-signal conditions. They use the same message structure and source encoding as that used in JT65.

The performance of JT2 may eventually be as good as JT65, or slightly better, at 144 MHz and below. The JT2 signal is very narrow - its total occupied bandwidth is just 8.75 Hz - so dozens of JT2 signals can be scattered at random in a 2500 Hz SSB transceiver bandwidth with no more than a few
accidental collisions.

If it can be made to work up to its potential, JT2 could be a great boon to random digital EME operation on 2 meters, especially for those without panoramic wideband receivers and software like MAP65. JT2 may also be attractive for use on the VLF, MF, and HF bands under weak-signal conditions.

Further information on JT2 and JT4

WSJT Website

No comments: