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1-18 (No.RA032<Rev.001>)
2.4.4 Transmitter System
2.4.4.1
Audio Band Circuit
The signal from microphone is amplified and converted to digital signal by IC902. IC902 includes AGC function.
Digital signal is transferred to IC706 thru SSI.
2.4.4.2
Base Band Circuit
The audio signal transferred from IC902 is processed at IC706. Voice signals of 300Hz or lower and frequencies of 3kHz or higher are
cut off and an audio range 300Hz to 3kHz is extracted. The audio signal is then pre-emphasized in FM mode and synthesized with
the signals, such as QT and DQT, as required, and is transferred to PLL Frequency Synthesizer block. The DTMF and MSK base
band signals are also generated by IC706.
In Digital mode, the audio signal is converted to the 4-Level FSK base band signal and is transferred to PLL Frequency Synthesizer
block.
The output level according to the transmit carrier is fine-adjusted according to each modulation method.
2.4.4.3
Drive and Final amplifier
The signal from the TX VCO is amplified by the pre-drive amplifier (IC300, Q300 and Q301). The output of the pre-drive amplifier is
amplified by the drive amplifier (Q302) and the final amplifier (Q303) to 30W at 700MHz or 35W at 800MHz band (2W when the power
is low). IC300 is MMIC. Q300, Q301, Q302, and Q303 are MOS FET.
The output of the final amplifier is then passed through the coupler, antenna switch (D305, D306, D308, D310, and D311), harmonic
filter (LPF) and applied to the antenna terminal.
2.4.4.4
APC circuit
The automatic transmission power control (APC) circuit controls the transmitter output in adjusted value by monitoring it with a coupler.
RF detection and comparison functions are included in the power-control IC (IC302).
The output of the power control IC is given as a drive source of each gate of the pre-drive amplifier (Q300 and Q301) and the drive
amplifier (Q302) and completes APC feedback loop.
When a normal antenna load is connected, reflected Forward RF Power is detected by the coupler and direct in the power-control IC
(IC302). Forward RF Power is converted into DC voltage in IC302 and is compared with APC1.
The output voltage goes through DC amplifier (IC303) to the pre-drive amplifier (Q300 and Q301) and the drive amplifier (Q302).
The voltage controls the gate bias1 voltage of Q300, Q301 and Q302, and keeps transmission output power stable.
SPC controls the gate bias2 voltage of Q303.
Fig.3 Drive and Final amplifier and APC circuit
2.4.5 PLL Frequency Synthesizer
2.4.5.1
TCXO (X700)
TCXO (X700) generates a reference frequency of 19.2MHz for the PLL frequency synthesizer. This reference signal is buffered by
Q700 and IC703. And it is distributed to PLL (IC100), IF IC (IC600), and IC706.
The frequency adjustment is achieved by switching the ratio of dividing frequency of PLL. The resolution of adjusting frequency is ap-
proximately 8Hz.
D305,306
ANT
D308,310
IC300
Q300
Q301
Q302
Q303
D311
TX VCO
Gate Bias1
Gate Bias2
Q305
Q306
IC302
D304
/DSW
/DSW
Q309
IC303
IC304
IC304
IC305
Q307
APC1
REV
SPC
Drive1
Pre -
Drive2
Drive3
Drive
Final
Coupler
ANT
ANT
REV
DC SW
DC
DC SW
DC SW
DC SW
AMP
Pre-
Pre-
AMP
DC
MP
PA
CONT
IC303
DC
AMP
DC
AMP
AMP
DC
DET
sw
LPF
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