Epson MFJ-1278B manual Pactor Feature Definitions, Digital Memory ARQ

MFJ-1278B MULTI-MODE BASIC OPERATION

As indicated in the preceding paragraph, the usual terminal/radio/modem parms are available.

As in Packet, Pactor also contains COMMAND and CONVERSE modes. Please note that switching between them is modeled on the "NEWMODE ON" procedures in packet. The MFJ- 1278B is in COMMAND mode, if the p_cmd: prompt is on the computer screen. To switch to CONVERSE mode from COMMAND mode the K key followed by an <ENTER> is issued by the user. The CMDCHR character switches the MFJ-1278B from CONVERSE mode back to COMMAND mode. The CMDCHR character is defined as CTRL-C. Once connected, the link acts much like AMTOR.

The station originating the connection is the master and he remains in transmit mode until he or the slave initiates a changeover. Either station may reverse the direction of the link by issuing a control-Y changeover (^Y) in converse mode.

PACTOR FEATURE DEFINITIONS

DIGITAL MEMORY ARQ

The MFJ-1278B's Pactor incorporates a Digital Memory ARQ mode. Digital Memory ARQ enables reconstruction of a good packet from a bad packet. A bad packet is one repeatedly received with on or more bit errors. Digital Memory ARQ accumulates the bit value, 1 or 0 derived from the RF port during successive reception of the same error-laden packet. These bit accumulations are sent to the receiver shift register. Thus a good packet is reconstructed from 2 or more "bad" packets.

The MAXSUM parameter controls the number of accumulations performed for each bit. Larger MAXSUM values increase the effectiveness of the Digital Memory ARQ scheme, but only to a certain point. The reception of an almost perfect packet will be inadequate to overcome the accumulated noise, if MAXSUM is too large. Also the presence of excessive QRM, QRN, or QSB effects the reception of good packets. On the other hand, if MAXSUM is too small the accumulation of samples will be too few to correct for moderate error rates. The factory setting for MAXSUM represents a good compromise--feel free to play with it.

FEC UNPROTO

Unproto: "FEC/UNPROTO" packets are transmitted UREPEATS+1 times. Selecting larger values of UREPEATS reduces throughput, but enhances reliability. To transmit in UNPROTO mode, issue the appropriate unproto command and type away. When done, break out to "p_cmd:" mode and type 'D' or 'DD' to terminate transmission.

MONITORING

Monitoring unproto: If MONITOR is except when connected to another station.

ON the MFJ-1278B is always in listen mode, There are other situations occur that prevent the