Motorola Gm328 Gm338 Gm398 Detailed 6804112j18 E Manual

							Technical Specifications1-3
Transmitter UHF
*Frequencies - Full BandsplitUHF 450-527 MHz
Channel Spacing12.5/20/25 kHz
Frequency Stability
(-30°C to +60°C, +25° Ref.)±2.0 ppm
Power 1-25W
Modulation Limiting
±2.5 @ 12.5 kHz 
±4.0 @ 20 kHz
±5.0 @ 25 kHz
FM Hum & Noise-40 dB @ 12.5kHz
-45 dB @ 20/25kHz
Conducted/Radiated Emission (ETS)-36 dBm 1 GHz
Adjacent Channel Power-60 dB @ 12.5 kHz
-70 dB @ 25 kHz
Audio Response (300 - 3000 Hz)+1 to -3 dB
Audio Distortion @1000Hz, 60%
Rated Maximum Deviation65 dB
Base Mode: >70dB 
(1-25W model only)
Adjacent Channel Selectivity (ETS)
65 dB @ 12.5 kHz 
70 dB @ 20 kHz
75 dB @ 25 kHz
Spurious Rejection (ETS)70 dB @ 12.5 kHz
75 dB @ 20/25 kHz
Rated Audio3W Internal
13W External
Audio Distortion @ Rated Audio
						

							1-4Technical Specifications
*Availability subject to the laws and regulations of individual countries.
Audio Response (300 - 3000Hz @ 20/25kHz)
(300 - 2550Hz @12.5kHz)+1 to -3 dB
Conducted Spurious Emission (ETS)-57 dBm 1 GHz
Receiver UHF 
						

							2-1
Section 2
THEORY OF OPERATION
1.0 Introduction
This Chapter provides a detailed theory of operation for the UHF circuits in the radio. For details of 
the theory of operation and troubleshooting for the the associated Controller circuits refer to the 
Controller Section of this manual.
2.0 UHF (450-527 MHz) Receiver
2.1 Receiver Front-End
The receiver is able to cover the UHF range from 450 to 527 MHz. It consists of four major blocks: 
front-end bandpass filters and pre-amplifier, first mixer, high-IF, low-IF and receiver back-end . Two 
varactor-tuned bandpass filters perform antenna signal pre-selection.  A cross over quad diode 
mixer converts the signal to the first IF of 44.85 MHz. Low-side first injection is used.
Figure 2-1 UHF Receiver Block Diagram
Demodulator
1. Crystal 
Filter Mixer Va r a c t o r  
Tuned Filter RF Amp Va r a c t o r  
Tuned Filter Pin Diode 
Antenna 
Switch
RF Jack Antenna
Control Voltage
from  PCICFirst LO
from FGU
Recovered Audio
RSSI
Second LO
2. Crystal 
Filter
455kHz Filter
(25kHz)455kHz Filter
(25kHz)
455kHz Filter
(12.5kHz)455kHz Filter
(12.5kHz)SwitchSwitchSwitchSwitch
Limiter
1. IF Amp
2. IF Amp
Filter Bank Selection
from  Synthesizer IC
   Harmonic 
   Filter
BWSELECT 
						

							2-2UHF (450-527 MHz) Receiver
There are two 2-pole 44.85 MHz crystal filters in the high-IF section and 2 pairs of 455 kHz ceramic 
filters in the low-IF section to provide the required adjacent channel selectivity .The correct pair of 
ceramic filters for 12.5 or 25 kHz channel spacing is selected via control line BWSELECT. The 
second IF at 455 kHz is mixed, amplified and demodulated in the IF IC. The processing of the 
demodulated audio signal is performed by an audio processing IC located in the controller section.
2.2 Front-End Band-Pass Filters & Pre-Amplifier 
The received signal from the radio’s antenna connector is first routed through the harmonic filter and 
antenna switch, which are part of the RF power amplifier circuitry, before being applied to the 
receiver pre-selector filter (C5001, C5002, D5001 and associated components). The 2-pole pre-
selector filter tuned by the varactor diodes D5001 and D5002 pre-selects the incoming signal (RXIN) 
from the antenna switch to reduce spurious effects to following stages. The tuning voltage 
(FECTRL_1) ranging from 2 volts to 8 volts is controlled by pin 20 of PCIC (U5501) in the 
Transmitter section. A dual hot carrier diode (D5003) limits any inband signal to 0 dBm to prevent 
damage to the pre-amplifier.
The RF pre-amplifier is an SMD device (Q5003) with collector base feedback to stabilize gain, 
impedance, and intermodulation. The collector current of approximately 11-16 mA is drawn from the 
voltage 9V3 via L5003 and R5002. A switchable 3dB pad (R5066,R5007,R5063, R5064 and 
R5070), controlled via line FECTRL_2 and Q5004 stabilizes the output impedance and 
intermodulation performance. 
A second 2-pole varactor tuned bandpass filter provides additional filtering of the amplified signal. 
The varactor diodes D5004 and D5005 are controlled by the same signal FECTRL_1, which 
controls the pre-selector filter. A following 1 dB pad (R5013 - R5015) stabilizes the output 
impedance and intermodulation performance.
2.3 First Mixer and High Intermediate Frequency (IF)
The signal coming from the front-end is converted to the first IF (44.85 MHz) using a cross over 
quad diode mixer (D5051). Its ports are matched for incoming RF signal conversion to the 44.85 
MHz IF using low side injection via matching transformers T5051 and T5052. The injection signal 
(RXINJ) coming from the RX VCO buffer (Q5332) is filtered by the lowpass filter consisting of 
(L5053, L5054, C5053 - C5055) followed by a matching transformer T5052 and has a level of 
approximately 15dBm.
The mixer IF output signal (IF) from transformer T5501 pin 2 is fed to the first two pole crystal filter 
FL3101. The filter output in turn is matched to the following IF amplifier.
The IF amplifier Q3101 is actively biased by a collector base feedback (R3101, R3106) to a current 
drain of approximately 5 mA drawn from the voltage 5V. Its output impedance is matched to the 
second two pole crystal filter FL3102. The signal is further amplified by a preamplifier (Q3102) 
before going into pin 1 of IFIC (U3101).
A dual hot carrier diode (D3101) limits the filter output voltage swing to reduce overdrive effects at 
RF input levels above -27 dBm. 
						

							UHF (450-527 MHz) Transmitter Power Amplifier (PA) 25 W 2-3
2.4 Low Intermediate Frequency (IF) and Receiver Back End
The 44.85 high IF signal from the second IF amplifier feeds the IF IC (U3101) at pin1. Within the IF 
IC the 44.85 MHz high IF signal mixes with the 44.395 MHz second local oscillator (2nd LO) to 
produce the low IF signal at 455 kHz. The 2nd LO frequency is determined by crystal Y3101. The 
low IF signal is amplified and filtered by an external pair of 455 kHz ceramic filters FL3112, FL3114 
for 20/25 kHz channel spacing or FL3111,FL3113/F3115 for 12.5 kHz channel spacing. These pairs 
are selectable via BWSELECT. The filtered output from the ceramic filters is applied to the limiter 
input pin of the IF IC (pin 14).
The IF IC contains a quadrature detector using a ceramic phase-shift element (Y3102) to provide 
audio detection. Internal amplification provides an audio output level of 120 mV rms (at 60% 
deviation) from U3103 pin 8 (DISCAUDIO) which is fed to the ASFIC_CMP (U0221) pin 2 (part of 
the Controller circuitry). 
A Received Signal Strength Indicator (RSSI) signal is available at U3101 pin 5, having a dynamic 
range of 70 dB. The RSSI signal is interpreted by the microprocessor (U0101 pin 63) and in addition 
is available at accessory connector J0501-15.
3.0 UHF (450-527 MHz) Transmitter Power Amplifier (PA) 25 W
The radio’s 25W PA is a three stage amplifier used to amplify the output from the VCOBIC to the 
radio transmit level. All three stages utilize LDMOS technology. The gain of the first stage (U5401) is 
adjustable, controlled by pin 4 of PCIC (U5501) via U5402-1.  It is followed by an LDMOS  stage 
(Q5421) and LDMOS final stage (Q5441).
Figure 2-2 UHF Transmitter Block Diagram 
Devices U5401, Q5421 and Q5441 are surface mounted. A pressure pad between board and the 
radios cover provides good thermal contact between the devices and the chassis.PCIC
Pin Diode 
Antenna 
Switch
RF JackAntenna
Harmonic 
Filter
PowerSensePA - F i n a lStag e From VCOControlledStag e
VcontrolBias 1Bias 2
To Microprocessor
Temperature
Sense SPI BUS
ASFIC_CMP
PA
PWR
SET
To Microprocessor
PADriver 
						

							2-4 UHF (450-527 MHz) Transmitter Power Amplifier (PA) 25 W
3.1 First Power Controlled Stage
The first stage (U5401) is a 20dB gain integrated circuit containing two LDMOS FET amplifier 
stages. It amplifies the RF signal from the VCO (TXINJ). The output power of stage U5401 is 
controlled by a DC voltage applied to pin 1 from the op-amp U5402-1, pin 1. The control voltage 
simultaneously varies the bias of two FET stages within U5401. This biasing point determines the 
overall gain of U5401 and therefore its output drive level to Q5421, which in turn controls the output 
power of the PA.
Op-amp U5402-1 monitors the drain current of U5401 via resistor R5444 and adjusts the bias 
voltage of U5401 so that the current remains constant. The PCIC (U5501) provides a DC output 
voltage at pin 4 (INT) which sets the reference voltage of the current control loop. A raising power 
output causes the DC voltage from the PCIC to fall, and U5402-1 adjusts the bias voltage for a lower 
drain current to lower the gain of the stage.
In receive mode the DC voltage from PCIC pin 23 (RX) turns on Q5442, which in turn switches off 
the biasing voltage to U5401.
Switch S5440 is a pressure pad with a conductive strip which connects two conductive areas on the 
board when the radios cover is properly screwed to the chassis. When the cover is removed, S5440 
opens and the resulting high voltage level at the inverting inputs of the current control op-amps 
U5402-1 & 2 switches off the biasing of U5401 and Q5421. This prevents transmitter key up while 
the devices do not have proper thermal contact to the chassis.
3.2 Power Controlled Driver Stage
The next stage is an LDMOS device (Q5421) providing a gain of 12dB. This device requires a 
positive gate bias and a quiescent current flow for proper operation. The bias is set during transmit 
mode by the drain current control op-amp U5402-2, and fed to the gate of Q5421 via the resistive 
network R5429, R5418, R5415 and R5416.
Op-amp U5402-2 monitors the drain current of U5421 via resistors R5424-27 and adjusts the bias 
voltage of Q5421 so that the current remains constant. The PCIC (U5501) provides a DC output 
voltage at pin 4 (INT) which sets the reference voltage of the current control loop. A raising power 
output causes the DC voltage from the PCIC to fall, and U5402-2 adjusts the bias voltage for a lower 
drain current to lower the gain of the stage.
In receive mode the DC voltage from PCIC pin 23 (RX) turns on Q5422, which in turn switches off 
the biasing voltage to Q5421.
3.3 Final Stage
The final stage is an LDMOS device (Q5441) providing a gain of 12dB. This device also requires a 
positive gate bias and a quiescent current flow for proper operation. The voltage of the line 
MOSBIAS_2 is set in transmit mode by the ASFIC and fed to the gate of Q5441 via the resistive 
network R5404, R5406, and R5431-2. This bias voltage is tuned in the factory. If the transistor is 
replaced, the bias voltage must be tuned using the Global Tuner.  Care must be taken not to 
damage the device by exceeding the maximum allowed bias voltage. The device’s drain current is 
drawn directly from the radio’s DC supply voltage input, PASUPVLTG, via L5436 and L5437.
A matching network consisting of C5441-49 and striplines transforms the impedance to 50 ohms 
and feeds the directional coupler. 
						

							UHF (450-527 MHz) Transmitter Power Amplifier (PA) 25 W 2-5
3.4 Directional Coupler
The directional coupler is a microstrip printed circuit, which couples a small amount of the forward 
power delivered by Q5441. The coupled signal is rectified by D5451. The DC voltage is proportional 
to the RF output power and feeds the RFIN port of the PCIC (U5501 pin 1). The PCIC controls the 
gain of stages U5401 and Q5421 as necessary to hold this voltage constant, thus ensuring the 
forward power out of the radio to be held to a constant value.
3.5 Antenna Switch
The antenna switch consists of two PIN diodes, D5471 and D5472. In the receive mode, both diodes 
are off. Signals applied at the antenna jack J5401 are routed, via the harmonic filter, through 
network L5472, C5474 and C5475, to the receiver input. In the transmit mode, K9V1 turns on 
Q5471 which enables current sink Q5472, set to 96 mA by R5473 and VR5471. This completes a 
DC path from PASUPVLTG, through L5437, D5471, L5472, D5472, L5471, R5474 and the current 
sink, to ground. Both diodes are forward biased into conduction. The transmitter RF from the 
directional coupler is routed via D5471 to the harmonic filter and antenna jack. D5472 also 
conducts, shunting RF power and preventing it from reaching the receiver port (RXIN). L5472 is 
selected to appear as a broadband lambda/4 wave transmission line, making the short circuit 
presented by D5472 appear as an open circuit at the junction of D5472 and the receiver path.
3.6 Harmonic Filter
Components L5491-L5493 and L5472, C5491, C5496-98 form a Butterworth low-pass filter to 
attenuate harmonic energy of the transmitter to specifications level.  R5491 is used to drain 
electrostatic charge that might otherwise build up on the antenna. The harmonic filter also prevents 
high level RF signals above the receiver passband from reaching the receiver circuits, improving 
spurious response rejection.
3.7 Power Control
The transmitter uses the Power Control IC (PCIC, U5501) to control the power output of the radio. A 
portion of the forward RF power from the transmitter is sampled by the directional coupler and 
rectified, to provide a DC voltage to the RFIN port of the PCIC (pin 1) which is proportional to the 
sampled RF power. 
The ASFIC (U0221) has internal digital to analog converters (DACs) which provide a reference 
voltage of the control loop to the PCIC via R5505. The reference voltage level is programmable 
through the SPI line of the PCIC. This reference voltage is proportional to the desired power setting 
of the transmitter, and is factory programmed at several points across the frequency range of the 
transmitter to offset frequency response variations of the transmitter’s power detector circuit.
The PCIC provides a DC output voltage at pin 4 (INT) which sets the drain current of the first 
(U5401) and second (Q5421) transmitter stage via current control op-amps U5402-1 and U5402-2. 
This adjusts the transmitter power output to the intended value. Variations in forward transmitter 
power cause the DC voltage at pin 1 to change, and the PCIC adjusts the control voltage above or 
below its nominal value to raise or lower output power.
Capacitors C5502-4, in conjunction with resistors and integrators within the PCIC, control the 
transmitter power-rise (key-up) and power-decay (de-key) characteristic to minimize splatter into 
adjacent channels. 
						

							2-6UHF (450-527 MHz) Frequency Synthesis
U5502 is a temperature-sensing device, which monitors the circuit board temperature in the vicinity 
of the transmitter driver and final devices, and provides a DC voltage to the PCIC (TEMP, pin 30) 
proportional to temperature. If the DC voltage produced exceeds the set threshold in the PCIC, the 
transmitter output power will be reduced so as to reduce the transmitter temperature.
4.0 UHF (450-527 MHz) Frequency Synthesis
The synthesizer subsystem consists of the reference oscillator (Y5261 or Y5262), the Low Voltage 
Fractional-N synthesizer (LVFRAC-N, U5201), and the Voltage Controlled Oscillator VCO.
4.1 Reference Oscillator
The reference oscillator (Y5262) contains a temperature compensated crystal oscillator with a 
frequency of 16.8 MHz. An Analogue to Digital (A/D) converter internal to U5201 (LVFRAC-N) and 
controlled by the microprocessor via serial interface (SRL) sets the voltage at the warp output of 
U5201 pin 25 to set the frequency of the oscillator. The output of the oscillator (pin 3 of Y5262) is 
applied to pin 23 (XTAL1) of U5201 via a RC series combination.
In applications where less frequency stability is required the oscillator inside U5201 is used along 
with an external crystal Y5261, varactor diode D5261, C5261, C5262 and R5262. In this case, 
Y5262, R5263, C5235 and C5251 are not used. When Y5262 is used, Y5261, D5261, C5261, 
C5262 and R5262 are not used, and C5263 is increased to 0.1 uF. 
						

							UHF (450-527 MHz) Frequency Synthesis2-7
4.2 Fractional-N Synthesizer
The LVFRAC-N synthesizer IC (U5201) consists of a pre-scaler, a programmable loop divider, 
control divider logic, a phase detector, a charge pump, an A/D converter for low frequency digital 
modulation, a balance attenuator to balance the high frequency analogue modulation and low 
frequency digital modulation, a 13V positive voltage multiplier, a serial interface for control, and 
finally a super filter for the regulated 5 volts.
Figure 2-3 UHF Synthesizer Block Diagram
A voltage of 5V applied to the super filter input (U5201 pin 30) supplies an output voltage of 4.5 
VDC(VSF) at pin 28. It supplies the VCO, VCO modulation bias circuit (via R5322) and the 
synthesizer charge pump resistor network (R5251, R5252). The synthesizer supply voltage is 
provided by the 5V regulator U5211.
In order to generate a high voltage to supply the phase detector (charge pump) output stage at 
pin 47 VCP (U5201-47), a voltage of 13 VDC is being generated by the positive voltage multiplier 
circuitry (D5201, C5202, C5203). This voltage multiplier is basically a diode capacitor network driven 
by two (1.05MHz) 180 degrees out of phase signals (U5201-14 and -15).
Output LOCK (U5201-4) provides information about the lock status of the synthesizer loop. A high 
level at this output indicates a stable loop. IC U5201 provides the 16.8 MHz reference frequency at 
pin 19.
The serial interface (SRL) is connected to the microprocessor via the data line DATA (U5201-7), 
clock line CLK (U5201-8), and chip enable line CSX (U5201-9).
DATA
CLK
CEX
MODIN
VCC, DC5V
XTAL1
XTAL2
WARP
PREIN
VCP
REFERENCE
OSCILLATOR
 VOLTAGE
MULTIPLIER
DATA (U0101 PIN 100)
CLOCK (U0101 PIN 1)
CSX (U0101 PIN 2)
MOD IN (U0221 PIN 40)
+5V (U5211 PIN 1)7
8
9
10
13, 30
23
24
25
32
47
VMULT2 VMULT1BIAS1 SFOUTAUX3 AUX4 IADAPTIOUTGND FREFOUTLOCK4
19
6, 22, 33, 44
43
45
3
2
28
       14
        1540FILTERED 5VSTEERING LOCK (U0101 PIN 56)
PRESCALER INFREF (U0221 PIN 34)
39 BIAS2
41
 48 5, 20, 34, 36
+5V (U5211 PIN 1)
AUX1 VDD, DC5VMODOUT
U5201 
LOW VOLTAGEFRACTIONAL-N
SYNTHESIZER
AUX21 (NU)
BWSELECTVCO Bias
TRB
To IF
SectionTX RF INJECTION
(1ST STAGE OF PA)LO RF INJECTION
VOLTAGE 
CONTROLLED 
OSCILLATORLINE
2-POLE
LOOP
FILTER 
						

							2-8UHF (450-527 MHz) Frequency Synthesis
4.3 Voltage Controlled Oscillator (VCO)
The Voltage Controlled Oscillator (VCO) consists of the VCO/Buffer IC (VCOBIC, U5301), the TX 
and RX tank circuits, the external RX buffer stages, and the modulation circuitry.
Figure 2-4 UHF VCO Block Diagram
The VCOBIC together with Fractional-N synthesizer (U5201) generates the required frequencies in 
both  transmit and receive modes. The TRB line (U5301 pin 19) determines which tank circuits and 
internal buffers are to be enabled. A high level on TRB enables TX tank and TX output (pin 10), and  
a low enables RX tank and RX output (pin 8). A sample of the signal from the enabled output is 
routed from U5301 pin 12 (PRESC_OUT), via a low pass filter, to pin 32 of U5201 (PREIN).
A steering line voltage (VCTRL) between 3.0V and 10.0V at varactor diode CR5311 will tune the full 
TX frequency range (TXINJ) from 450 MHz to 527 MHz, and at varactor diodes CR5301, CR5302 
and CR5303 will tune the full RX frequency range (RXINJ) from 405 MHz to 482 MHz. The tank 
circuits uses the Hartley configuration for wider bandwidth. For the RX tank circuit, an external 
transistor Q5301 is used in conjunction with the internal transistor for better side-band noise. 
Similarly, an external transistor Q5311 is used in the Tx tank circuit.
 
Presc
RX
TXMatching
NetworkLow Pass
    Filter
Attenuator Pin8
Pin14
Pin10(U5201 Pin28)
VCC Buffers
TX RF Injection U5201 Pin 32 AUX3 (U5201 Pin 2)
Prescaler Out
Pin 12 Pin 19 Pin 20
      TX/RX/BS
Switching Network
U5301
VCOBIC
       Rx
Active Bias
      Tx
Active Bias
Pin2
Rx-I adjustPin1
Tx-I adjustPins 9,11,17
Pin18Vsens
Circuit Pin15Pin16 RX VCO
 Circuit
TX VCO
 Circuit RX Tank
TX TankPin7
Vcc-Superfilter
Collector/RF in
Pin4
Pin5
Pin6
RX
TX
(U5201 Pin 28)Rx-SW
Tx-SW
Vcc-Logic
(U5201 Pin 28) Steer Line 
Voltage 
(VCTRL)Pin13
Pin3TRB IN
LO RF INJECTION
Q5301
Q5332