Starting with WSJT-X 2.0, the FT8 and MSK144 protocols convey a 77-bit
payload.  For most purposes these bits are interpreted as 3 bits (i3)
for message type and 74 for user information.  Any message type that
uses fewer than 74 information bits can assign the remaining bits to
define message subtypes. For example, Type i3=0 uses 71 information
bits and the remaining 3 bits, here called n3, define 8 possible
subtypes.

----------------------------------------------------------------------------------
i3.n3 Example message                    Bits           Total  Purpose
----------------------------------------------------------------------------------
0.0   FREE TEXT MSG                      71               71   Free text 
0.1   K1ABC RR73; W9XYZ <KH1/KH7Z> -12   28 28 10 5       71   DXpedition Mode
0.2   PA3XYZ/P R 590003 IO91NP           28 1 1 3 12 25   70   EU VHF contest
0.3   WA9XYZ KA1ABC R 16A EMA            28 28 1 4 3 7    71   ARRL Field Day
0.4   WA9XYZ KA1ABC R 32A EMA            28 28 1 4 3 7    71   ARRL Field Day
0.5   123456789ABCDEF012                 71               71   Telemetry (18 hex)
0.6   K1ABC RR73; CQ W9XYZ EN37          28 28 15         71   Contesting
0.7   ... tbd

1     WA9XYZ/R KA1ABC/R R FN42           28 1 28 1 1 15   74   Standard msg
2     PA3XYZ/P GM4ABC/P R JO22           28 1 28 1 1 15   74   EU VHF contest
3     TU; W9XYZ K1ABC R 579 MA           1 28 28 1 3 13   74   ARRL RTTY Roundup
4     <WA9XYZ> PJ4/KA1ABC RR73           12 58 1 2 1      74   Nonstandard calls
5     ... tbd
6     ... tbd
7     ... tbd
----------------------------------------------------------------------------------
In case we need them, later:

5     TU; W9XYZ K1ABC R 579 8 MA         1 28 28 1 3 6 7  74   CQ WW RTTY
6     TU; W9XYZ K1ABC R 579 MA           1 28 28 1 3 13   74   CQ WPX RTTY
----------------------------------------------------------------------------------
NB: three 74-bit message types and two 71-bit message subtypes are still TBD.
----------------------------------------------------------------------------------

The 28-bit fields normally used for callsigns are configured rather
differently from before.

Facts about the 28-bit integers used to encode standard callsigns:
  2^28              = 268,435,456  Available values
  37*36*10*27*27*27 = 262,177,560  Used for standard callsigns
                      -----------
                        6,257,896  Difference
  2^22              =   4,194,304  Used for 22-bit hash codes
                      -----------
                        2,063,592  available for CQ, CQ nnn, CQ xxxx, QRZ, ...


Further details on message types:
-----------------------------------------------------------------------------
i3.n3
-----------------------------------------------------------------------------
0.0 Free text, up to 13 characters.

0.1 DXpedition mode, as developed for KH1/KH7Z.

0.2 Report, QSO serial number from 0001 to 4095, 6-character grid, and Roger
    for EU VHF contests.

0.3 ARRL Field Day exchange (1-16 transmitters).

0.4 ARRL Field Day exchange (17-32 transmitters).

0.5 Telemetry, 71 bits

1.  Two callsigns, Roger, and grid or report.  Each callsign may have
    an appended "/R" to indicate Rover status for NA VHF contests.
    Either callsign may be nonstandard if enclosed in angle brackets,
    for example <YW18FIFA>.

2.  Same as Type 1, but uses /P instead of /R.  For European VHF contests. 

3.  Standard message for ARRL RTTY Roundup.  Optional "TU;" at
    beginning to finish a previous QSO; then two standard callsigns,
    optional "R", a 3-bit report (529 to 599), and 13 bits to indicate
    US state, Canadian province/territory, or DX serial number from
    0001 to 7999.

4.  One hashed call or "CQ"; one compound or nonstandard call with up
    to 11 characters; and (if not "CQ") an optional RRR, RR73, or 73.

---------------------------------------------------------------------------
The following are tentative and not included in first release.

5.  CQ WW RTTY  - US/Can: RST CQZ state/prov  R 579 5 NJ       R1 r3 z6 u7
                  DX:     RST + CQzone        R 559 15         R1 r3 z6
	     
6.  CQ WPX RTTY - RST + serial                R 589 0013       R1 r3 n12
