5.4 Block Description
5-12
RX CIRCUIT
The Rx signal reduce out-of-band signals/noise between 156.025 MHz and 162.025
MHz by BPF (L/C) on Q7 input/output circuit and Q7 (RF AMP) will amplify it by
10dB. CR 104 is 1
st
MIXER circuit that converts RX signal by 1
st
Local of Fo＋51.2375
MHz into 1
st
IF signal of 51.2375 MHz.
Fo - (Fo+51.2375 MHz) = 51.2375 MHz
1
st
IF signal, after being amplified by Q6 and Q111, will be converted by 2
nd
MIXER
circuit of CR106 and 2
nd
local of 51.2 MHz. 51.2 MHz is created by multiplying
reference frequency of 25.6 MHz received from CPU board by 2 on U11.
51.2375 MHz - 51.2 MHz = 37.5 kHz
This signal of 37.5 kHz is inputted into CPU board as RX IF OUT signal and is
demodulated with CODEC and DSP. AGC is a circuit that controls CR9 and CR13 (pin
diode) when AGC voltage is inputted from CPU board. However, since this voltage is
always set to 1.1 V regardless of RX input level, technically, AGC is not being used.
TX/RX IF out:
- measures no modulation signal input with J9 - #27 on TX RX board
SP SINAD:
- measures SP output (1 W) of 1 kHz/70 % MOD.
Fig. 5.4.6 Input/Output(RX) characteristic on TX/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
TX/RX IF out
SP SINAD
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