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G6KUI > HELP 29.07.04 10:50l 39 Lines 1587 Bytes #999 (0) @ WW
BID : 76463-G6KUI
Read: GUEST DL9GB
Subj: Re: 7plus Information
Path: DB0FHN<DB0FOR<DB0SIF<DB0EA<DB0RES<ON0AR<GB7CIP<GB7COV<GB7DBY<GB7DBY
Sent: 040729/0935z @:GB7DBY.#23.GBR.EU NPF2.54c [G6KUI PMS Alvaston Derby]
Matthew KC0AYG asked.......
}
} I have been working on a python program for a packet radio project and I
} need to convert a binary file (in this case weather radar data) into
} something the packet network will handle. Given the prevelence of 7plus
} its seems like a logical choice, however there is no tool included in the
} python langauge for 7plus (if only life were that easy). I searched some
} of the web looking for information on the 7plus specification thinking
} perhaps I could write my own tool, but have so far come up with nothing
} more then the C source code (which sadly I read rather poorly). Does
} anyone have more information or could point me in the right direction?
}
Have a look at the 7plus instruction manual.
It describes fully as to how 7plus works.
Using the info in this manual, I was able to manually decode a previously
small simple 7plussed file.
Basically all 7plus does is take blocks of (8bit) data and convert it bit
by bit into 7(and a little more) bits of data and then add a checksum at
the end of each line. Each original character ends up as part of 2 or 3
final characters.
You start off with 256 possible combinations ( characters) and end with
something like 210 as certain characters are absent from the encoded
output - these characters are the ones that BBS's use internally and/or
are normally filtered out of BBS text messages.
I think there is a list given of the absent codes (characters).
7plus then adds some header and footer info and splits it into parts if
required.
73, Pete G6KUI
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