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USER'S GUIDE
1.1.
Definition and Standards References
AMTOR (Amateur Teleprinting Over Radio) is a microprocessor-controlled, error-correcting
data communications system.
AMTOR is derived directly from the commercial practice known as SITOR (Simplex Telex
Over Radio), as described in Recommendations 476-2 and 476-3 of the CCIR (International
Consultative Committee on Radio, an agency of the International Telecommunications
Union, and in turn, of the United Nations. These international commercial standards were
adapted for amateur use in 1977 by J. Peter Martinez, G3PLX.
AMTOR is now permitted in many countries, including the United States of America, as spe-
cifically defined in Part 97.69 of the Rules of the Federal Communications Commission.
1.2.
Application
Like SITOR, AMTOR uses synchronous transmission of a seven-bit information code to
achieve essentially error-free message and text communications. The transmit function enc-
odes all characters with a mark-to-space polarity ratio, always as four ones and three zeros,
thus allowing the receiving station's processor to check for that ratio.
There are two basic AMTOR modes. In the ARQ mode (also called Mode A), Station A sends
a block of three characters during an interval of 210 milliseconds. The sending system then
pauses for 240 milliseconds, during which Station B transmits a single acceptance code.
1.3.
Mode A – ARQ
In the interactive ARQ mode, all transmitted characters are sent in blocks or groups, each
containing three characters. This mode operates between two synchronized or phased sta-
tions.
If the receiving system's processor detects an incorrect mark-to-space (ones-to-zeros) polar-
ity ratio, the receiving station's processor or computer sends a command back to the send-
ing station's processor or computer to retransmit the invalid group of characters.
No data are displayed on the screen at the receiving site until it has passed this test, been
validated and is essentially error-free.
Data transmission is at 100 bauds, corresponding to a character length of 70 milliseconds.
The overall cycle time for a three-character block and the control signal reply is 450 millisec-
onds.
If the information has been received incorrectly, Station B issues a 'request for repetition'
(RQ) code. Receiving the RQ code, Station A repeats the three-character block. This process
repeats until Station B transmits a second control code, an acceptance code, after which the
next three characters are sent as a. block.
Station A displays the transmitted text on its display device only after receiving the accept-
ance code from Station B. This is called 'echoing.'
PK232UG Rev. E 9/87
APPENDIX E – AMTOR THEORY
E-1
AMTOR THEORY
185
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