QRA64 - Un nuovo metodo di trasmissione " weak signals" inserito nel software WSJT-X

Tratto dal collegamento :

http://physics.princeton.edu/pulsar/k1jt/v1.7_Features.txt

La presentazione :

http://www.eme2016.org/wp-content/uploads/2016/08/EME-2016-K1JT-Presentation.pdf

Alpha Release: WSJT-X Version 1.7
  ---------------------------------

Short list of new features
--------------------------
1.  New modes: ISCAT, MSK144, QRA64.
2.  Newly implemented submodes: JT65B-C, JT9B-H (wide and fast).
3.  FT decoder replaces KV decoder for JT65; KVASD is no longer used.
4.  Improvements to JT4, JT9, and JT65 decoders.
5.  Multi-pass decoding for JT65 and WSPR.
6.  Many improvements to Rig Control.
7.  Improved convenience features for EME Doppler tracking.
8.  Multiple configurations can be saved and restored.
9.  Sample-file download facility.
10. Optional auto-sequencing for "fast" modes.

New Modes
---------
1. MSK144 is intended for meteor scatter at 50 MHz and higher.
Designed and tested by K9AN and K1JT, it uses a low-density parity
check code (LDPC) -- one of the latest-and-greatest areas of active
research in communication theory.

MSK144 is a direct descendant of the now-defunct mode JTMSK, with a
number of improvements for better performance on weak and short meteor
pings.  The effective character transmission rate is about 250 cps,
compared with 147 cps for FSK441 and 154 cps for JTMSK.  Like JT4,
JT9, JT65, and JTMSK, MSK144 uses strong forward error correction, so
message decoding is essentially "all or nothing".  You will see little
or no garbage on your screen.

Standard MSK144 message frames are 72 ms long, compared to 117 ms for
JTMSK.  The MSK144 waveform allows coherent demodulation, allowing up
to 3 dB better sensitivity.  After QSO partners have exchanged
callsigns, MSK144 can use even shorter messages, only 20 ms long.  As
in all the fast modes in WSJT-X, the 20 ms or 72 ms messages are
repeated without gaps for the duration of a transmission cycle.  For
most purposes we recommend a T/R cycle duration of 15 s, but 5 s and
10 s sequences are also supported.

Short ("Sh") messages in MSK144 are intended primarily for 144 MHz,
where most pings are short.  These messages do not contain full
callsigns; instead, they contain a hash of the entire transmitted
message along with a report.  They are not encrypted -- the report is
sent in the clear along with the hash.  Short messages are fully
decodable only by the station to whom they are addressed, as part of
an ongoing QSO, because only then will the received hash match that
calculated using the known strings for "My Call" and "DX Call" and the
received report, RRR, or 73.  If you are monitoring someone else's
QSO, you will not be able to decode its Sh messages.

An MSK144 signal occupies the full bandwidth of a typical SSB
transmitter, so transmissions are always centered at an offset of
1500Hz.  For best results, selectable/adjustable Rx and Tx filters
should be set to provide the flattest possible response over at least
300 - 2700 Hz.  The maximum permissible frequency offset between you
and your QSO partner is 200 Hz, and less is better.

2. QRA64 is a intended for EME and other weak-signal use.  Its
internal code was designed by Nico Palermo, IV3NWV, and implemented in
WSJT-X by K1JT.  The protocol uses a "Q-ary Repeat Accumulate" code,
another one of the latest research areas in communication theory.  The
QRA64 code is inherently better than the Reed Solomon (63,12) code
used in JT65, yielding already a 1.3 dB advantage.  QRA64 uses a new
synchronizing scheme based on a 7 x 7 Costas array, so you will not
see a bright sync tone at the lowest tone frequency.  This change
yields another 1.9 dB advantage.

In most respects our implementation of QRA64 is operationally similar
to JT65.  QRA64 does not use two-tone shorthand messages, and it makes
no use of a callsign database.  Rather, additional sensitivity is
gained by making use of "already known" information as a QSO
progresses -- for example, when reports are being exchanged and you
have already decoded both callsigns in a previous transmission.  QRA64
presently offers no message averaging capability, though that may be
added.  In our early tests, many EME QSOs have already been made using
submodes QRA64A-E on bands from 144 MHz to 10 GHz.

3. ISCAT is essentially the same as in recent versions of program WSJT.
For details consult the WSJT User Guide:
http://physics.princeton.edu/pulsar/K1JT/doc/wsjt/


Program Setup
-------------

Many of the new program capabilities are enabled when you check
"Enable VHF/UHF/Microwave features" on the Settings | General tab.
For MSK144 mode, we suggest setting "T/R 15 s" and "F Tol 100 Hz".
Check "Sh" to enable the use of short messages and "Auto Seq" for
auto-sequencing.  For QRA64 mode, set Tx and Rx frequencies to 1000
Hz.  We encourage you to check "Save all" when making tests, and to
save any of the resulting .wav files that might help us to improve
program performance or behavior, or to illustrate a problem that you
identify.


Final Comments
--------------

Remember that you are using an Alpha Release.  We will be grateful for
any and all reports from test users that may help us to further
improve WSJT-X.  The most helpful reports describe the problem clearly
and include a complete recipe to reproduce it.  Send your reports to
wsjtgroup@yahoogroups.com.

Please be patient concerning responses from the development group.
Several of us will be on vacation or otherwise engaged during much of
August.