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THEORY OF OPERATION
This is a PLL - controlled VHF and UHF dual band marine transceiver provides an accurate and stable
multi-channel operation.
The transceiver consists of 8 main sections:
Transmitter
Receiver
Low voltage detection
Vibration Alert
Voice recorder
VOX
Local oscillator PLL (Phase Lock Loop) Circuit
Memory backup
Transmitter
The audio is picked up from the internal MIC, the audio signal is then amplified by Audio Amplifier, U9
LM324 (4/4), U9 (1/4) and filtered by a low pass filter U9 (2/4). The audio is divide into two paths VHF and
UHF.
UHF
The audio is adjusted with VR2 to obtain a suitable Audio frequency response, and then modulated with
the carrier by VCO, through Q13. When the unit is transmitting, the audio signal is added to the TX VCO
Q13. The capacitance of Cbc varied following the audio signal and when mixed with the carrier to form the
modulated signal. The modulated signal output from the VCO is pre-amplified by Q11, D14, Q10, Q9 and
D5. Then it is amplified by Q2, Q1 .The amplified signal then passes through a match network that
consists of C79, L3, and the antenna switching circuit D1, L37, D7. The signal is filtered by another
low-pass filter circuit which consists of C55, L10, C59, C63, L2, C58, C1, L1 and C54. These low pass
filters are necessary to suppress the second and third harmonics. The signal is then fed into the antenna
input and radiated out.
VHF
The audio is adjusted with VR3 to obtain a suitable Audio frequency response, and then modulated
with the carrier by VCO, through D15. When the unit is transmitting, the audio signal is added to the
TX VCO D15. The capacitance of D15 varied following the audio signal and when mixed with the
carrier to form the modulated signal. The modulated signal output from the VCO is pre-amplified by
Q12, D12, Q5, Q4 and D5. Then it is amplified by Q2, Q1 .The amplified signal then passes through a
low-pass network that consists of L14, C77, and the antenna switching circuit D3, L16, D4. The signal
4
Summary of Contents for MR HH425 LI VP
Page 7: ...BLOCK DIAGRAM BACKLIGHT BACKLIGHT 7 ...
Page 11: ...Main PCB Top View Bottom View VR3 VR2 VC1 L44 L46 SQL L45 11 ...
Page 12: ...WIRING DIAGRAM CHARGER CHARGER 12 ...
Page 13: ...Main PCB Top View PRINTED CIRCUIT BOARD SQL 13 ...
Page 14: ...Main PCB Bottom View PRINTED CIRCUIT BOARD 14 ...
Page 15: ...Charger PCB PRINTED CIRCUIT BOARD Top View Bottom View LCD PCB Bottom View Top View 15 ...
Page 18: ...MAIN UNIT EXPLODED VIEW 18 ...
Page 19: ...CHARGER UNIT EXPLODED VIEW 19 ...
Page 20: ...BATTERY TRAY UNIT EXPLODED VIEW 20 ...
Page 48: ...U4 9032 HT D 48 ...
Page 49: ...U5 M38C29FFAHP60K 49 ...
Page 50: ...2 1 3 1 VOUT 2 VSS 3 VIN Delay Circuitry Vref VSS VOUT VIN U6 XC61FC4012MR U7 U8 U9 NJM324 50 ...
Page 51: ...1 2 3 4 8 7 6 5 A0 A1 A2 GND VCC WP SCL SDA U AT C N 11 24 16 U12 XC6204B502MR 51 ...