Kenwood NXR-800 Service Manual page 13

3-3. Forward/Refl ect power detector circuit
The forward / Refl ect power detector circuit consists of a
CM coupling type detection circuit formed by a Micro strip
line and the differential amplifi er IC4.
A part of the transmitter power is detected by diodes D9
and D10 and is converted into DC voltage.
Directional coupler
Foward
ATT
D9
DET Diff. AMP
Fig. 10 Forward/Refl ect power detector circuit
3-4. Antenna switch
If a common antenna is used for the transmitter signal
and receiver signal, switch transmitter and receiver signals
by connecting CN19 to the RX Unit.
If different antennas are used for the transmitter and re-
ceiver, it functions as an On/Off switch for the transmitter
circuit.
3-5. Harmonic fi lter circuit
The harmonic filter circuit uses a three-stage "pi" type
Chebyshev type LPF.
This circuit removes harmonics from the transmitter out-
put and sends the fi ltered signal to the antenna connecter
(CN22).
Pin
CIRCUIT DESCRIPTION
Reflect
ATT
IC4
D10
DET
IC10
RA13H4452M101
VGG VDD Pout
HPF
IC2
Diff. AMP
Fig. 11 APC circuit
3-6. APC circuit
The APC circuit stabilizes the transmitter power so that
the output power specifi ed by the Control Voltage from the
MPU is obtained. It consists of a Forward/Refl ect power
detector circuit and Differential amplifi ers (IC2 and IC5).
It compares the voltage detected by the Forward/Refl ect
power detector circuit (voltage detected by the Forward
Power) and the Control Voltage (PWR_CONT) from the
MPU (IC802: X56-312 A/3). It stabilizes the output power
by changing pin 2 (Vgg).
The voltage detected (that detected Reflect Power) by
the Forward/Refl ect power detector circuit is compared to
the Control Voltage (PWR_PRT) from the MPU (IC802: X56-
312 A/3). When a load V.S.W.R. is connected to the An-
tenna Connecter and is more than 1.5, it functions so that
the output power gets smaller as the detection voltage (that
detected Refl ect Power) gets larger.
3-7. High temperature detector circuit
The high temperature detector circuit consists of a ther-
mal switch IC (IC7) and a switching FET (Q2).
This circuit lowers the transmitter power when the fi nal
unit temperature is too high (83°C or higher).
Pin
Fig. 12 High temperature detector circuit
Directional coupler
Foward Reflect
ATT ATT
D9 D10
DET DET
IC4
Diff. AMP
+
IC5
Add. AMP
Diff. AMP
NXR-800
IC10
RA13H4452M101
VGG VDD
Pout
IC7
Q2 Temp
protection
SW
IC
PWR_PRT
PWR_CONT
13