From: Mike Davies (otmr@kobayanda.com)
Date: Thu Sep 18 2003 - 21:48:08 EEST
I'm trying to find out what happens at the physical level with
Ax25 packet. I've tried looking at the source code but either I'm looking
in the wrong place, or I don't understand.
I'm assuming tones of 1200Hz and 2200Hz for 1200bps
I have several questions concerning transmission.
1) Am I right in thinking that the tone changes every time a zero
bit is sent, and not changed when a 1 bit is sent? If so, what tone
frequency do I start with (for the first zero bit in the $7E frame start
octet)
2) Which order are the bits sent ? LSB or MSB first ?
3) What is the polynomial for the frame check CRC. I have seen two
quoted, x^16 + x^12 + x^5 + 1 and also x^16 + X^15 + x^2 + 1 which is
right, or is it something else ?
4) Given that one of the tones is the same as the baud rate, i.e.
one complete cycle for one bit, does it matter where in the cycle I start
the tone ?
5) I'm assuming there is no phase shift between bits. Is this
correct ?
Mike de G0WZY
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