Several people have asked for an update on development of the "Fast
modes" in WSJT and WSJT-X. So here's a brief summary.
First, a review of some relevant terms and motivations. It's convenient
to think of the various WSJT protocols ("modes") in two groups:
*Slow modes* -- JT4, JT9, JT65, and WSPR. These modes are designed for
communication with extremely weak signals -- often too weak to be heard.
Target propagation modes include EME and long-distance troposcatter on
VHF-and-up bands, and QRP Dxing on the LF, MF, and HF bands. Relevant
signal amplitudes are approximately constant over a minute and more,
aside from so-called "libration fading" for EME. Transmit/receive
sequences are 1 minute for JT4, JT9, and JT65, and 2 minutes for WSPR.
*Fast modes* -- JTMS, FSK441, ISCAT, and JT6M -- and now also *FSK315*
(implemented in WSJT) and *JT9E* through *JT9H* (implemented in WSJT-X).
These modes are made for communication with rapidly varying signals:
for example, meteor scatter, ionospheric scatter, airplane scatter, and
scatter off the International Space Station. The decoders are designed
take advantage of short enhancements of signal strength. T/R sequences
are 30 seconds (or sometimes even shorter).
Bill, ND0B, has implemented a trial version of FSK315 in WSJT. Think of
this mode as FSK441 slowed down to 315 baud; the bandwidth is therefore
narrow enough to make the mode legal in the "CW and data" portion of the
10 meter band. Bill and a few others have been experimenting with
FSK315 and also ISCAT-A on 10 meters, under dead-band conditions, using
meteors and ionospheric scatter propagation.
I have implemented experimental submodes of the JT9 protocol in the
program branch WSJT-X v1.6.1. As with JT4 and JT65, letters following
the "JT9" designator indicate increased spacings between the FSK tones.
Traditional JT9 (now also called JT9A) has tone spacing 1.736 Hz, so
the signals used at HF and below have total bandwidth 9*1.736 = 15.6 Hz.
The widest of the new submodes, JT9H, has tone spacing 200 Hz and
therefore bandwidth 9*200 = 1800 Hz.
When used with the standard 1-minute periods, the wide JT9 submodes
should be useful for the same purposes as the wide JT4 submodes:
microwave EME, for example, where libration fading can cause Doppler
spreading of 100 Hz or more. Used in this way, all JT9 submodes are
"slow" modes; they use 1-minute T/R periods and keying rate 1.736 baud,
and they send the full 85-symbol message protocol in 85/1.736 = 48.96 s.
Optionally, the wide JT9 submodes can now also use "fast" keying rates
equal to their tone spacing. "Fast JT9H", for example, uses keying rate
200 baud, so the full message protocol is transmitted in 85/200 = 0.425
s. The message is sent repeatedly for the full Tx period, in the same
way as done for the other fast modes.
The fast JT9 submodes should be very effective for meteors and
ionoscatter propagation, especially on the 6 meter band. Sensitivity
should be similar to ISCAT, or perhaps slightly better. Because JT9
includes strong forward error correction, decoding results are like
those for all the slow modes: you should see messages exactly as they
were transmitted, or nothing at all.
Tests of the fast JT9 submodes are currently under way, with excellent
results.
-- 73, Joe, K1JT
------------------------------------------------------------------------------
_______________________________________________
wsjt-devel mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/wsjt-devel
