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Add info on 28-bit integers used for standard callsigns.

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This commit is contained in:
Joe Taylor 2018-06-23 11:54:40 -04:00
parent 7266d407ff
commit 35b53766cb
1 changed files with 16 additions and 4 deletions
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20
lib/77bit/77bit.txt
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@ -1,6 +1,9 @@
Proposed new message types have a 77-bit payload: 74 information bits
and 3 bits for "message type" i3. Type 0 uses only 71 information
bits, releasing another 3 bits (call them n3) to define 8 sub-types.
Proposed new message types have a 77-bit payload. For most purposes
these are interpreted as 3 bits (i3) for "message type" and 74
information bits. 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 subtypes.
----------------------------------------------------------------------------------
i3.n3 Example message Bits Total Purpose
@ -11,7 +14,8 @@ i3.n3 Example message Bits Total Purpose
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 0123456789abcdef01 71 71 Telemetry (18 hex)
0.6
0.6
0.7
1 WA9XYZ/R KA1ABC/R R FN42 28 1 28 1 1 15 74 Standard msg
2 TU; W9XYZ K1ABC R 579 MA 1 28 28 1 3 13 74 ARRL RTTY contest
@ -29,6 +33,13 @@ In case we need them, later:
NB: three 74-bit message types and two 71-bit message subtypes are still TBD.
----------------------------------------------------------------------------------
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 Needed for standard callsign structure
11*10*10*27*27*27 = 21,651,300 nnnaaa, _nnaaa (n=digit, a=letter or blank)
2^24 = 16,777,216 available for 24-bit hash code
4,874,084 available for special CQs, etc.
The 28-bit callsign field includes about 19 million impossible "calls"
that start with three digits. That's more than 2^24 = 17,777,216, so
these values could be used to implement a 24-bit CRC -- in addition to the
@ -60,6 +71,7 @@ Further details:
4. One nonstandard call with up to 11 characters, one hashed call,
followed by <blank>, RRR, RR73, or 73.
---------------------------------------------------------------------------
The following are tentative, not to be included in first release:
5. CQ WW RTTY - US/Can: RST CQZ state/prov R 579 5 NJ R1 r3 z6 u7