Furuno FM-8800, Руководство по обслуживанию

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5.4 Block Description
5-9
160 MHz band RX signal of from DUPLEXER will be amplified by approximately 7
dB. BPF (L/C) of 156 to 163 MHz range is installed on Q1 input/output circuit. CR10
and 11 are 1
st
MIXER circuit that converts 160 MHz band RX signal into 1
st
IF signal of
51.2375 MHz by Fo
＋
51.2375 MHz.
Fo - (Fo + 51.2375 MHz) = 51.2375 MHz
1
st
IF signal amplified by Q13 and 14 is converted into 2
nd
IF signal of 37.5 kHz by 2
nd
local of 51.2 MHz on 2
nd
MIXER circuit of CR8/9. 51.2 MHz is created by multiplying
reference frequency of 25.6 MHz received from CPU board by 2 on U3.
51.2375 MHz - 51.2 MHz = 37.5 kHz
This 37.5kHz signal is inputted into CPU board as DUP IF OUT and is demodulated
with CODEC and DSP.
DUP RX IF out:
-measures no modulation signal input with J3 - #14 on DUP RX board.
SP SINAD:
-measures SP output (1W) of 1 kHz/70 % MOD. .
Fig. 5.4.4 Input/Output characteristic on DUP RX Board
--10 0 10 20 30 40 50 60 70 80 90 100
110dBuV
-60
-50
-40
-30
-20
SSG Level
Level(dBm)
SINAD(dB)
-10
0
10
20dB
0.77Vrms
2.4Vrms
7.7mVrms
DUP RX IF out
SP SINAD
1mVrms