Furuno FM-8800, Руководство по обслуживанию, Страница: 153 / 268

5.4 Block Description
5-21
Audio signal from the Transceiver handset, Remote handsets, and Wing MIC are
digitized on U10: CODEC (A/D conversion) and is inputted into U20: DSP. DSC TX
message is inputted into DSP from U30: CPU. These data are processed in DSP as DDS
setup data. Although a signal of FM-modulated 45 MHz is outputted from DDS (9 x 5
MHz) , this signal uses a high frequency that is 9 times higher than reference frequency
of DDS which is 5 MHz.
DEMODULATION
IF signal (-60 to +10 dBm) of 37.5 kHz from TX/RX board and DUP RX board goes
through U22 and limiter circuit of CR4. Then, it is amplified by differential amplifier
consisting of U11 and is inputted into U17: CODEC.
IF signal (-60 to +10 dBm) of 37.5 kHz from CH70 RX board goes through limiter
circuit of CR7 and is amplified by differential amplifier consisting of U18. Then it is
inputted into U17: CODEC. Below block diagram shows the demodulation process
carried out in DSP.
Fig. 5.4.17 DSP function Diagram
De-emphasis
FSK DEMOD
DEMOD
SEL
BPF
ATT ADJ.
LPF
LPF
Mute HPF/BPF
SQ Cont.
100kHz
100kHz
50kHz
6kHz
U10:
CODEC
U20: DSP
CH70 IF OUT
DUP RX IF OUT
TX/RX IF OUT
D/A
U17:
CODEC
A/D
D/A
U30:
CPU
Control
Control
De-emphasis
Enable/unenable
FSK DEMOD
Enable/unenable
Select
IF Sig.
Loop
back
FM DEMOD OUT(V
oice)
FSK Sig.
FM DEMOD (V
oice)
Separator
(Noise/Sig.)
DET.
(IF Sig. level)
DET.
Voice spectrum
SQ DET.
Calculation:
ATT
ATT
(AGC Cont.)
Judgment
(0 or 1)
Sampling
Reciveing level(ANT Bar IND.)
SQ VR data, SQ auto, SQ off
Loop back
Not used
EXT SP
VDR SP
HS SP
REM LINE OUT
(LINE OUT/VDR)
(TR Handset,
TR SP)