[50mhz] Tests of Experimental Modes in WSJT8

[Lance Collister, W7GJ]

Of particular interest to us for 6m DXing via Ionospheric hopping, are the very 
positive results of the "ISCAT" mode.  I hope we can see the future development of 
this very sensitive mode so that it is quick and a more effective choice over weak 
SSB and CW on marginal multihop Es and F2.  Here is how Joe summed up the tests:


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:
----------------------------------

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:
-----------------------------------

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?
--------------------

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

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-- 
Lance Collister, W7GJ (ex: WN3GPL, WA3GPL, WA1JXN, WA1JXN/C6A, ZF2OC/ZF8, E51SIX)
P.O. Box 73
Frenchtown, MT  59834  USA
QTH: DN27UB
TEL: (406) 626-5728
URL: http://www.bigskyspaces.com/w7gj
2m DXCC #11/6m DXCC #815

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