Watkins-Johnson Company WJ-8711A, Installation, Operation And Maintenance Manual

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CSMA REMOTE CONTROL WJ-8711A DIGITAL HF RECEIVER
5-18
5.9
COLLISION DETECTION
Many different data transmitting devices can be connected on the CSMA interface along with
the WJ-8711A. Therefore, there is always the possibility that two or more units may want to talk at the same
time, causing “data collisions” on the interface.
The WJ-8711A is designed so that it monitors all the messages that it transmits and then
compares the monitored data to the transmitted data. If the transmitted data does not match the monitored
data, it is assumed that a collision has occurred. The WJ-8711A immediately sends the jammer codes shown
in
Figure 5-22 . The WJ-8711A waits for a period of time, checks for an idle interface, and then sends the
original response. If another collision occurs, the process is repeated with an increased wait until the message
goes through or until the fifth repetition. After five tries (each with an increased wait), the WJ-8711A
discards the message. Only when the controller transmits a new message does the process start again. If any
device detects the jammer codes, the data that it receives is disregarded.
FC FC
FC FC FC
87IL27
Figure 5-22. Jammer Code
Courtesy of http://BlackRadios.terryo.org