To: Users of WSJT
From: K1JT
My sincere thanks to all who have provided feedback on the experimental testing of WSJT8!
The main purpose of these tests was to generate many on-the-air recordings of signals using the four new experimental modes JTMS, ISCAT, JT64, and JT8. These modes use a variety of schemes for synchronization, source encoding, error-control coding, and modulation -- most of them quite different from the protocols in WSJT7. The tests were aimed at establishing how well each scheme performs under challenging weak-signal conditions. This goal has been accomplished very effectively, and I'm grateful to all those who sent me their recordings.
Here are some early conclusions based on the many reports received from around the world.
First, some technical results:
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1. The synchronization, coding, and modulation schemes built into JT8 and JT64 are effective. Both modes work well at HF; they also work well for EME (although not with the decoders that were distributed in WSJT8 r1944). The decoders for both modes are sub-optimal in a variety of ways, sometimes annoyingly so. They would need further work before they could be declared suitable for a production release of WSJT8.
2. The modulation and coding scheme in JTMS works well for meteor scatter at VHF. In particular, it has been clearly established that MSK ("minimum shift keying") is a viable modulation technique for the MS path. Phase locking of a signal can be done reliably over the duration of meteor pings and bursts. The bandwidth efficiency of MSK is very attractive. A clear disadvantage of JTMS relative to FSK441 is that JTMS cannot make good use of pings shorter than about 75 ms.
3. The ISCAT mode is highly effective for its intended purpose -- ionospheric scatter at 50 MHz -- and also for multi-hop Es signals too weak for successful SSB or CW QSOs. I now have on hand many examples of recorded ISCAT signals that decode perfectly while being essentially inaudible and invisible on the waterfall display.
Now, some user-level results:
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4. Many successful QSOs have been made with each of the new experimental modes, both on their primarily intended propagation paths and on others. The WSJT8 decoders are less polished and slower than those in WSJT7 (as was known to be true, even before any field tests were solicited).
5. Some users in IARU Region 1 are unhappy with the structured message formats of JTMS and ISCAT, even though these structures are a super-set of the well accepted ones in JT65. The reluctance seems to arise from a wish to adhere strictly to procedures for MS QSOs dictated in Appendix 4, "Revised Meteor Scatter Procedures", described in the VHF/UHF/Microwaves Committee Report Interim Meeting, Vienna 2004 (see www.physics.princeton.edu/pulsar/K1JT/vie04_02.rtf).
On this side of the Atlantic, we consider a QSO valid when operators have exchanged callsigns, signal reports, and rogers. We do not dictate the precise arrangement of information in the transmissions conveying these bits of information.
The Region 1 VHF Managers Handbook, updated in May 2010, adopts the same approach as used here in Region 2 (see
www.physics/princeton.edu/pulsar/K1JT/VHF_Handbook_V5_42.pdf ,
pp. 98-105). The WSJT8 message structures fully support the requirements for valid QSOs laid out in the 2010 Handbook, which (I have assumed) supersedes the 2004 document. If I am mistaken, I hope someone will correct me.
6. Apparently someone has concluded (and "explained" to others) that hashed callsigns are not usable by a DXpedition because the operator would want to decode more than one caller while a QSO is going on. In fact, there is no such problem. Hashed callsigns can be used very effectively in such a situation. Many stations could be calling the DX operator at once, and no confusion need arise over who is calling and who is being worked. No doubt if WSJT8 is to survive, its eventual User's Guide will need to give more examples, in order to allay this fear.
The Bottom Line?
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Each of the experimental modes is effective, and much has been learned from their development and testing. However, the presently available results do not support a conclusion that JT64 will provide substantial advantages over JT65, or JT8 over JT4, or JTMS over FSK441. ISCAT is clearly superior to JT6M in many -- perhaps most? -- circumstances, but its decoder will need to be made faster if the mode is to become popular.
Happily, it seems likely that a number of lessons learned while developing and testing JTMS, ISCAT, JT64, and JT8 can be back-ported to the traditional WSJT7 modes with good effect. I intend to spend some weeks looking into these possibilities before making a final decision on whether WSJT8 merits further work.
As always, the views of others will be gratefully received!
-- 73, Joe, K1JT
