Transmitter System; Pll Frequency Synthesizer; Audio Band Circuit; Base Band Circuit - Kenwood NX-5800 Service Manual

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 pre-drive amplifier (IC300). The output of the pre-drive amplifier is amplified by the drive
amplifier (Q300) and RF Power module (IC302) to 45W (5W when the power is low).
IC300 is MMIC.Q300 is MOS FET. The output of the final amplifier is then passed through the coupler, antenna switch (D310, D311,
D312, D313, D314 and D315), 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 (IC304).
The power control IC output is given as a drive source of the RF power module's gate (IC302), and completes APC feedback loop.
When an normal antenna load is connected, reflected Forward RF Power is detected by the coupler and direct in power-control IC
(IC304).Forward RF Power is converted into DC voltage in IC304 and is compared with the APC1.
The output voltage goes through DC amp (IC301 2/2) to Drive amp (Q300) and RF Power module (IC302).
The voltage controls the gate bias1 voltage of Q300 and IC302, and keeps transmission output stable. SPC controls the gate bias2
voltage of IC302 too.
IC300
TX VCO
Pre-
Drive
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 adjusting a D/A converter (IC715) output in the voltage of the control terminal of TCXO.
1-16 (No.RA017<Rev.002>)
Q300 IC302
Drive Final
Gate Bias 2
Gate Bias 1
Q304
APC1
DC SW
DC DC
SPC
AMP AMP
IC303 1/2 IC303 2/2
Coupler
IC304 D309
PA REV
APC1
CTRL DET
DC DC
AMP AMP
IC301 1/2
IC301 2/2
MP
D310,311
ANT
D312,313
D314,315
ANT ANT
SW LPF
REV