Monday, July 21, 2014

Fun with WSJT-X

Since this weekend's ARRL 100th Convention, I've been trying out WSJT-X, the latest from Joe Taylor K1JT in his series of "Weak Signal" programs.  It supports the JT65 and JT9 digital modes, mainly for HF communications (1.8 - 30 MHz).  It's a more modern and user-friendly program than the original WSJT.

The JT65 mode, shown here as a waterfall spectrogram in the 17 M band, is Joe's classic mode.  It uses 64 tones plus a pilot to convey the digital message in a ~200 Hz band.  This selection is interesting, because the weak WSJT-X signal (JA1VGV) is hidden behind a strong RTTY station -- the two big vertical bars.  The JA station is -17 dB relative to the SSB noise level, while the RTTY signal is probably > 0 dB. 

A contact goes in 1 minute "chunks": sending for one minute (actually, 48 sec.) and receiving for one minute.  The divisions of transmit/receive are shown as red horizontal lines. (The waterfall is stopped for 48 sec during transmit.)

I use two power levels for JT65. Normal is 5 Watts.  When conditions are tough, I can ramp up to "QRO" -- 20 Watts.  To go higher than that is considered unsporting, I think!

JT65 is nice, but JT9 is better.  It uses the same message structure, but with only 9 tones that are spaced more closely.  JT9 is much more efficient in terms of spectrum utilization (by a factor of ~10), so it is clearly a better solution for crowded HF bands.  Unfortunately, most of the JT65 software now in use does not support JT9.  WSJT-X supports both.

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