Baudot is the standard mode for transmitting teletype over shortwave radio. It uses a 5 bit code, which only allows for 32 symbol total, obviously not enough for all the letters, digits, and punctuation. Therefore, two special characters may be transmitted - letters shift (LTRS) and figures shift (FIGS). These two modes determine which character will actually be printed when a 5 bit symbol is received.
The various buttons in the Signal Window perform the following operations:
 
These buttons select the baud rate.
 
These buttons select the shift frequency.
 
The N button selects Normal shift, the I button selects Inverted shift. The ABC button acts as an LTRS shift, and will return the program to letters mode, from figures mode. Very useful if a burst of noise shifts the program into numbers mode.
Tuning Indicator:
 
As shown above, tune your radio so that two spikes are visible, representing the mark and space tones. You want to center between these tones to be centered as close as possible. Select the appropriate shift frequency using one of the five shift buttons, described above.
 
When properly tuned, the mark/space tones are represented by black and white pulses. Gray means the audio tone is neither a mark or space. If you see gray mixed in (or all gray), then either the station isn’t properly tuned in, or the shift isn’t correct.
Select the combination of speed and polarity (Normal or Inverted) for proper display of decoded text.
Transmit Mode:
Selecting Transmit Mode (from the Control menu, or ⌘-T) will place MultiMode in the transmitting mode. RTTY audio will played out the Mac’s sound and/or speaker ports. Characters that you type will be converted into baudot code at the selected baud rate and shift. During transmission, the DTR line of the selected serial port will be active, this may be used as a PTT signal to a transmitter.
Macro keys are available to store commonly used phrases. There are 36 of them, and they are selected by holding down control and option while typing a letter or number.
There is a file that came with MultiMode called MACROS. This is a text file that you can edit with SimpleText. Here are the first three lines of the file:
0|This is Macro 0
1|This is Macro 1
2|This is Macro 2
The first two characters in each line are special - the first one identifies which macro is being defined, and is a digit from 0 to 9, or a letter from A to Z. This is followed by a | symbol. After that, you may type the text to be sent when that macro key is selected, up to 255 characters long.
