Klein 3900 Series Operation And Maintenance Manual page 28

1-10
CHAPTER 1 Overview
The data from the towfish arrives in serial NRZ format and is conditioned and
input to the clock recovery circuit. The recovered clock is used to strobe the
serial data into a line decoder. The decoded data is converted to parallel format
and output the front panel connector.
The downlink modulator is used to indicate to the towfish when to fire the
main array and to send commands to the towfish. The modulator uses FSK
modulation and is frequency multiplexed before being amplified and combined
with 200-volt power which is then transmitted down the tow cable. The CPU
board controls the modulator.
Series 3900 Sonar System Operations and Maintenance Manual 11214510, Rev. 02