2-10
THEORY OF OPERATION
Figure 2-1
UHF Transmitter Block Diagram
Device Q4401 is surface mounted. Q4421, Q4431 and Q4441 are directly attached to the heat sink.
5.1
Power Controlled Stage
The first stage (U4401) amplifies the RF signal from the VCO (TXINJ) and controls the output power
of the PA. The output power of the transistor U4401 is controlled by a voltage control line feed from
the PCIC pin4(U4501). The control voltage simultaneously varies the bias of two FET stages within
U4401. This biasing point determines the overall gain of U4401 and therefore its output drive level
to Q4421, which in turn controls the output power of the PA.
In receive mode the voltage control line is at ground level and turns off Q4473 which in turn switches
off the biasing voltage to U4401.
5.2
Pre-Driver Stage
The next stage is a 13dB gain LDMOS device (Q4421) which requires a positive gate bias and a
quiescent current flow for proper operation. The voltage of the line PCIC_MOSBIAS_1 is set in
transmit mode by PCIC pin 24 and fed to the gate of Q4421 via the resistive network R4480, R4416
and R4415. The bias voltage is tuned in the factory.
5.3
Driver Stage
The following stage is an enhancement-mode N-Channel MOSFET device (Q4431) providing a gain
of 10dB. This device also requires a positive gate bias and a quiescent current flow for proper
operation. The voltage of the line Bias_2_UHF_PA_1 is set in transmit mode by the ASFIC and fed
to the gate of Q4431 via the resistive network R4632, R4631, R4485 and R4486. This bias voltage
is also tuned in the factory. If the transistor is replaced, the bias voltage must be tuned using the
P C I C
Pin Diode
Antenna
Switch
RF Jack
Antenna
Harmonic
Filter
Power
Sense
PA-Final
Stage
PA
Driver
From VCO
Controlled
Stage
Vcontrol
Bias 1
Bias 2
To Microprocessor
Temperature
Sense
SPI BUS
A S F I C _ C M P
PA
PWR
SET
To Microprocessor
Pre
Driver
Summary of Contents for 6864115B62-C
Page 1: ...Professional Radio GM Series Detailed Service Manual 6864115B62 C ...
Page 2: ...ii ...
Page 4: ...iv ...
Page 5: ...Professional Radio GM Series Service Maintainability Issue July 2007 ...
Page 8: ...ii ...
Page 22: ...2 10 MAINTENANCE ...
Page 25: ...Professional Radio GM Series Controlhead Service Information Issue July 2007 ...
Page 77: ...Professional Radio GM Series Controller Service Information Issue May 2007 ...
Page 100: ...2 2 TROUBLESHOOTING CHARTS ...
Page 104: ...3 4 Controller schematics parts list ...
Page 154: ...3 52 Controller T12 Schematic Diagrams ...
Page 155: ...Professional Radio GM Series VHF 136 174MHz Service Information Issue May 2007 ...
Page 164: ...1 6 MODEL CHART AND TECHNICAL SPECIFICATIONS ...
Page 176: ...2 12 THEORY OF OPERATION ...
Page 186: ...3 10 TROUBLESHOOTING CHARTS ...
Page 190: ...4 4 VHF PCB SCHEMATICS PARTS LISTS ...
Page 252: ...4 66 VHF 1 25W PCB 8471235L02 Schematics VHF 136 174 MHz IF ...
Page 256: ...4 70 VHF 1 25W PCB 8471235L02 Schematics ...
Page 257: ...Professional Radio GM Series UHF 403 470MHz Service Information Issue May 2007 ...
Page 266: ...1 6 MODEL CHART AND TECHNICAL SPECIFICATIONS ...
Page 366: ...2 12 THEORY OF OPERATION ...
Page 372: ...3 6 Low Band TROUBLESHOOTING CHARTS ...