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[aprssig] PHG calculators

Robert Bruninga bruninga at usna.edu
Mon Jan 12 17:46:41 UTC 2009


>> The / character seems to be missing 
>> from the raw packet, it should be 
>> right after the PHGR, as specified in 
>> http://aprs.org/newN/probes.txt ...
>> So, make it... "PHG54404/FRSTAD W3" 
>> and it'll start to work.

Just so everyone understands, there was a weakness in the
original SPEC about what follows the various 7 byte fields such
as

CSE/SPD
PHGxxxx
DFSxxxx
RNGxxxx

In the original APRS, it was assumed that a "/" or SPACE
delimiter would follow these fields to separate them from any
optional following text and make them more human readable.  It
turns out that this was not specified in the spec, and so there
are as many interpretations of when the optional text begins as
there are parsers out there. 

Normally, this was not an issue, because the only purpose of the
optional following text was for human consumption anyway.  That
was why we proposed adding the extra PERIOD byte to the PHG
construct, since it would only push the optional text a little
to the right, but still be
Readable.

HOWEVER, now that we have defined the FREQUENCY field to be the
first 10 bytes of "optional text" wherever it may occur in a
Mic-E, or any other position or object report, then the presence
or absence of this DELIMITER becomes an issue.

BOTTOMLINE.  Use the PHGxxxxP format with caution, and never use
it when you are also going to follow with a FREQUENCY, or your
frequency will not get parsed.  For example, the D710 followed
the spec and did not allow for the possibliity of a delimiter
between those fields and a following FREQ.

Just FYI..

Bob, Wb4APR




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