The banner graphics
The banner above was designed using 'gimp' on a Linux workstation.
During the hours spent on designing the graphics, I learned a lot
about 'gimp', which basically was my motivation for spending so much
time designing it. It is probably very naive, but it was fun making it.
Appart from the obvious fax-page on the left, there is a 'signal-space
diagram' that shows the complex signal-points plotted in a Re/Im coordinate
system. Basically, a point (marked with a cross) designates a given
four-bit binary sequence. The distance of a point from the center indicates
what amplitude the modulation carrier must have to transmit the given four-bit
binary sequence, while the angle indicates how much the carrier has to be
phase-shifted. With 16 signal-points, there is one point for each possible
four-bit sequence, which makes it possible to transfer 4 bits in one
"symbol-period" or "baud". In V.29 there are 2400 symbol periods per second,
which gives a bit-rate of 4 x 2400 => 9600 bit/s.
The curve is what a given set of signal-points may translate
into in terms of digital samples, which gradually gets smoothed as they
turn analog somewhere along the line before they finaly reach the destination
fax-machine.
The background is basically random sequences of 0/1, but a repeating
pattern of '01111110' can be seen, which is the "flag-sequence" used
in the synchronous HDLC link-level protocol used among other places, in fax
transfers.
|