Hi all,
Regular readers of this list will know there has been much recent
development work on the experimental mode QRA64.
In the current code revision, r7322, QRA64 uses a wider spacing between
tones in its thrice-replicated Costas 7x7 sync pattern. Sync tones are
now transmitted at tone numbers {20 50 60 0 40 10 30} rather than the {2
5 6 0 4 1 3} pattern used up to r7297. This means that the old and new
sync patterns are incompatible. Henceforth, all tests with QRA64 should
be done using WSJT-X code revision 7322 or later for both Tx and Rx.
QRA64 was designed especially for VHF-and-up use, especially over the
EME path. Submodes QRA64A-E are now supported and generally work well,
even on paths with considerable Doppler spread. If you choose to
experiment with QRA64 on the HF bands, please use submode A. On
higher-frequency bands, simulations and on-the-air measurements suggest
optimum choices of submodes roughly as follows:
Doppler Submode Suggested EME bands
Spread
---------------------------------------
0 - 5 Hz A 50 - 432 MHz
5 - 20 B 1296 MHz
10 - 50 C 2.3 GHz
20 - 100 D 3.4, 5.7 GHz
50 - 200 E 10.3, 24 GHz
On any and all bands, please report results of your experimentation here!
Some algorithmic details are not yet optimized, either for sensitivity
or execution speed. You can reasonably expect further improvements to
the decoder in coming weeks.
Please join me in again thanking Nico Palermo, IV3NWV, who designed the
basic codec for QRA64 -- including novel features for handling Doppler
spreads that may be even larger than the tone spacing.
-- 73, Joe, K1JT
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