Kantronics KAM Operation Manual

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Kantronics KAM Operation Manual Manual pdf 48 page image

AMTOR44AMTOR ModeKAM onlyAMTOR TheoryInformation transmitted by AMTOR is specially encoded to provide a scheme of error detection.This coding takes the form of each character containing 4 SPACE signals and 3 MARK signals. Thereceiving station can use this 4/3 ratio to determine if the character received is "probably" correct.If the received signal were to arrive with 4 MARK and 3 SPACE signals, the signal is obviously in er-ror and the receiving station could take the appropriate action. The information is transmitted inblocks of 3 characters, that is, the sending station will transmit 3 characters and then pause for ananswer from the receiving station. The answer will consist of a single character, indicating that theblock just sent was either received OK or that the block should be retransmitted.AMTOR operation is possible in two basic modes. Mode A operation is a one-on-one mode, en-abling the receiving station to request retransmission of any characters received which contain er-rors. This mode provides a high degree of error immunity due to the handshaking between thetwo stations involved in the communication. This mode is commonly referred to as ARQ. Mode Boperation is similar to RTTY operation, in that the signals are not error-checked by a specific sta-tion and no handshaking is performed. Mode B is the mode for calling CQ or other operationswhere more than one station is intended to receive the communication. Mode B operation is calledFEC – Forward Error Correction. In this mode, each character is sent twice, and the receiving sta-tions will check each character for the proper 4/3 ratio. If the first character received is correct, itis printed and the next one ignored. Otherwise, the second character is checked and if it is correct,then it is printed. If neither character was received correctly, then a special character will be dis-played on the terminal to replace the invalid character. On the KAM, the default character is aspace, but you may choose any character you wish with the MISSCHAR command.A variation of the Mode B operation is called SELFEC – Selective FEC. In this mode, the sendingstation would cause a specific receiving station to automatically enter the receive mode and copythe signal – thus is selectively starts the receiver.AMTOR stations are each identified with a SELCAL – the selective callsign used to identify this sta-tion from all others. In most amateur communication, we think of the callsign being used for thispurpose, but in AMTOR, the SELCAL is normally composed of the first letter of your call and thelast three letters of your call. Thus the SELCAL for KA5ZTX would be KZTX. If your callsign doesnot contain four letters, the standard practice is to duplicate the first letter of the SELCAL. ThusWK5M would have a SELCAL of WWKM. The SELCAL is used in both the SELFEC and ARQ modesof operation.With the implementation of the CCIR 625 recommendation for AMTOR operation, the SELCAL maynow contain 7 characters. This SELCAL cannot include the characters G, H, J, L, N and W. The rea-sons for this are contained in the 'Comité Consultatif International des Radiocommunications'"CCIR Recommendation 491-1" which describes a TOR station identity.The KAM allows you to enter this 7 character SELCAL in two ways. First, you may enter the actual7 characters you wish to use. Currently, there is no defined standard for selecting your 7 charac-ters. The second option in the KAM is to enter a 9 digit number. The KAM will then calculate thecorresponding SELCAL in accordance with 625.Once you have entered your MYSEL7 and MYSEL4, the KAM will automatically respond to eitherSELCAL for a mode A (ARQ) QSO, or (if AUTOSTRT is ON) for a SELFEC mode B (FEC) transmis-sion.