On 03/01/2019 12:07, Martin Davies G0HDB wrote:
Just out of interest, is there any particular technical reason why the
extra 'word' for inclusion
in a directional CQ message couldn't incorporate numeric characters as
well as letters? It
would add a bit more flexibility to directional CQ'ing, eg. the
ability to call CQ to say W6 or
UA0.
Hi Martin,
it is simply a size limitation, adding the possibility of one of ten
digits to each of 4 character positions increases the permutations from
27 x 27 x 27 x 27 = 531441 and requires 19 bits
to
37 * 37 * 37 * 37 = 1874161 and requires 20 bits
actually, due to message specific compression algorithms, the value used
to encode this word shares some bits with the possibility of a standard
callsign, a hashed callsign, part of a non-standard or compound callsign
(the remained goes in the part of the message that would usually hold a
gridsquare, signal report, R+signal report, RRR, 73, or RR73), QRZ, DE,
or CQ and a 3 digit numeric values use for MS split working from a
calling frequency. Even this is an over-simplification but hopefully you
get the idea.
Whatever way you look at it, there are not enough bits in a 77-bit
payload to represent both letters and digits for directional CQ calls
without giving up some other possible message types.
73
Bill
G4WJS.
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