MOSAIC II Version 1.22.

30/08/98

This version of MOSAIC II transmits audio tones via a "Hamcomm" type interface
connected to a PC serial port, for transmission via an SSB transmitter. It
generates human-readable text in the frequency domain, and is read with the help
of a spectrograph program.

These transmissions, called Sequential Multi Tone Hellschreiber, or S/MT-Hell
are extremely immune to man-made and atmospheric noise and interference. MOSAIC II
is ideally suited for transmission on the lower HF bands, such as 80 and 40m.
MOSAIC II transmissions are, with the correct settings, completely compatible
with all other known Amateur MT-Hell systems.

This version has a 7 x 5 dot matrix and has a limited range of transmit tones.
It is easily read on other software such as EVM MT-Hell by G3PLX and MTHELL by
G3PPT. This version is still under development, and does not have some of the
features exhibited in other versions. For example, there is no F6 key, no F10
key, and no double size text (as yet).

Generating clean tones via a serial interface is very difficult. This software
uses a pulse-width modulation technique, where five bit sine wave tones are
modulated on a 115200 baud data stream. The low pass filter in the "Hamcomm" interface
removes the 115200 Hz (bit rate) and 16457 Hz (character rate) carriers, leaving a
relatively smooth sine wave signal. Despite the high carrier frequency, the range of
usable tones is very limited - divisors of 16 to 22, created with character based
sine tables 16 to 22 characters long - generate precise tones from 1029 Hz down to
748 Hz with an average spacing of 47 Hz. To achieve the fine spacing required for
MT-Hell, intermediate frequencies are synthesized from segments of these sine tables,
resulting in tone average spacings of 22 and 11 Hz. The narrow spaced tones carry
some sidebands at the tone difference frequency due to these imperfections, but these
are insignificant compared to the keying sidebands are do not affect operation.

The tones are not equally spaced in frequency - they are at constant period
increments. The result is slight but unnoticeable distortion of the character
shapes. At wide shift the spacing varies from 36 to 61 Hz, and has the main effect
of compressing the lower case descenders.

One of the ramifications of using 115200 baud as the data stream frequency is that
the software will only work correctly on a 16550 UART - not on earlier PCs with
8250 based serial ports. If the baud rate were to be lowered, say to 38400 baud,
the tone frequencies would be either unacceptably low - 343 Hz to 249 Hz - or
the tone spacing would be too great.
Unzip the archive into a suitable directory and adapt 150.CFG to suit your callsign.
I don't suggest messing with the menu items until you are familiar with the various
modes I have set up - the menu is set for best use of the restricted range of tones
available. You must have 150.CFG and 150.EXE in the same directory. This file
(150.TXT) is optional and its removal will not affect operation.

Unlike other versions of this program (which can transmit any tone in 1 Hz steps
via the PC speaker), this version does not calculate tone frequencies on the fly.
Only three tone settings are allowed. These are selected by a "width" parameter,
as follows:

Width    Average Spacing    Tones Hz
======== =============== ===================================
  1       10 Hz           784  794  804  813  823  834  845
  2       22 Hz           784  804  823  845  866  890  914
  3       47 Hz           748  784  823  866  914  968 1029

This does of course limit the range of suitable transmission speeds, for example
it is not much use below 5 pixels/sec, but this has not been found in practice to be
a problem. The ability to use a "Hamcomm" interface for generating good clean tones
easily compensates for any other shortcomings. This version also correctly
operates the "Hamcomm" PPT signal to key the transmitter using a "KOX" technique.

Full instructions for receiving equipment and general use of all MOSAIC II
Versions are to be found in the file MOSAIC2.TXT.

Enjoy yourself - and I hope to SEE you in Hell!

Murray ZL1BPU
as149@detroit.freenet.org