Kantronics KAM Operation Manual

Also see for KAM: Manual Command manual Instruction manual Installation manual

Kantronics KAM Operation Manual Manual pdf 42 page image

RTTY / ASCII38RTTY and ASCII ModesKAM onlyRTTY TheoryRTTY is a 5 level (5 bit) BAUDOT code, which limits the number of possible characters to 32. Thisobviously does not provide enough combinations for all 26 letters of the alphabet and the numer-als and punctuation. Therefore, in order to allow more combinations, two special characters havebeen reserved as a FIGURES shift and LETTERS shift. When you first enter the RTTY Mode, thesystem is in the LETTERS shift, thus allowing normal alphabetic characters to be typed. When youtype any numbers or punctuation, the KAM automatically inserts a FIGURES shift prior to sendingthe character. One FIGURES shift is sent prior to the beginning of a string of numbers, but if aspace is typed, a new figures shift will be required. You may manually insert a FIGURES shift bytyping a Ctrl-N or a LETTERS shift by typing a Ctrl-L. If this is done, the KAM will not insert theFIGURES shift for you, for that sequence of numbers.The standard mechanical teletype machine always "un-shifted" when it received a space character,thus any numerals or punctuation immediately following a space will require a FIGURES shift to in-sure, that the receiving machine is in the FIGURES mode. The KAM simulates this un-shiftingbased on the setting of the USOS command.When operating in RTTY, standard procedure is to transmit approximately one line of RYs prior toactually typing your message. This allows the receiving station time to properly tune his stationand adjust his receiving equipment. This was particularly true with the older mechanical units, buthas carried over into today's computer terminal RTTY operation. A typical sequence, then, for call-ing CQ might look like this:RYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYCQ CQ CQ DE WK5M WK5M WK5MCQ CQ CQ DE WK5M WK5M WK5MCQ CQ CQ DE WK5M WK5M WK5M K K KThe RY has been used for the synchronizing and testing purpose because in the 5 level Baudotcode, this represents a complete reversal of the bit pattern, therefore the receiving mechanicalmachine had to completely reverse all levers all levers and gears within the time frame of onecharacter. It was felt that if the machine could do a complete reversal like this, it could copy anyother combination without problem.RTTY is transmitted using FSK (Frequency Shift Keying) in which two possible conditions for eachbit of data are sent as two distinct frequencies. These are called MARK and SPACE, and the differ-ence between these two frequencies is called the SHIFT. Most amateur RTTY is transmitted with a170 Hz shift, but other common shifts used are 425 Hz and 850 Hz. With FSK, the frequencies aregenerated by changing the actual carrier frequency of the transmitter. Another method of transmit-ting RTTY is to generate the tones within a piece of equipment and then modulate the carrier withthe tones. This is called AFSK (Audio Frequency Shift Keying). The KAM supports both methods oftransmitting RTTY and ASCII signals as well as all three of the standard shifts. In addition, theKAM can use non-standard shifts by selecting MODEM SHIFT and setting your own choice of MARKand SPACE tones.ASCII is an 8 bit code, allowing 256 possible combinations and thus overcomes the shortcomingsof RTTY concerning numbers and punctuation. Because all possible numbers, letters and punctua-tion can be defined within this set of of combinations, no LETTERS or FIGURES shift is required.Transmission of ASCII is accomplished using FSK or AFSK as is done in Baudot RTTY and many ofthe operational practices have been carried forward from RTTY to ASCII.