Furuno CN-24, Service Manual

Page: 7 / 90

1-3
1.3.1 SYNC Code
The synchronous signal consists of 32bits binary coded data.
The DN SYNC code is attached to the beginning of each transmission cycle to enable the
display unit identifying the signal. The coded pulses enable to reduce the effect of noise
along the transmission line to the paravane receiver.
The S/N ratio becomes maximum when the number of bits is 2
n
-1 (n: integer), 31 bits out
of these 32 bits are actually used in the display unit. Fig. 1.5 shows the 32 bits code data.
Fig. 1.5 SYNC Code (DN SYNC)
The UP SYNC signal inserted before the catch monitor data consists of 15 bit binary code
data and is used to stabilize the oscillation line of the upward sounding picture on the
display unit.
For the modulation of the sync codes, the FS (Frequency Shift) modulation is employed; "1',
and "0" are modulated at frequencies which are different by 1kHz each other, as shown
bellow.
Code/Frequency
Transmission Frequency 0 1
33 kHz 33 kHz 34 kHz
40 kHz 40 kHz 41 kHz
50 kHz 50 kHz 51 kHz
1.3.2 Temperature Data
The water temperature is indicated by the time interval from the left edge of the
temperature data region to the temperature signal (15 bit H/L code). The temperature data
region is allocated next to the DN SYNC code.
Fig. 1.6 Temperature data region
Depending on the temperature, the time from the left edge varies.
Temperature signal (15 bit H/L code)