Motorola Gm328 Gm338 Gm398 Detailed 6804112j18 E Manual

							UHF (403-470 MHz) Frequency Synthesis2-7
4.2 Fractional-N Synthesizer
The LVFRAC-N synthesizer IC (U4201) 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 (U4201 pin 30) supplies an output voltage of 4.5 
VDC(VSF) at pin 28. It supplies the VCO, VCO modulation bias circuit (via R4322) and the 
synthesizer charge pump resistor network (R4251, R4252). The synthesizer supply voltage is 
provided by the 5V regulator U4211.
In order to generate a high voltage to supply the phase detector (charge pump) output stage at 
pin 47 VCP (U4201-47), a voltage of 13 VDC is being generated by the positive voltage multiplier 
circuitry (D4201, C4202, C4203). This voltage multiplier is basically a diode capacitor network driven 
by two (1.05MHz) 180 degrees out of phase signals (U4201-14 and -15).
Output LOCK (U4201-4) provides information about the lock status of the synthesizer loop. A high 
level at this output indicates a stable loop. IC U4201 provides the 16.8 MHz reference frequency at 
pin 19.
The serial interface (SRL) is connected to the microprocessor via the data line DATA (U4201-7), 
clock line CLK (U4201-8), and chip enable line CSX (U4201-9).
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 (U4211 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 (U4211 PIN 1)
AUX1 VDD, DC5VMODOUT
U4201 
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 (403-470 MHz) Frequency Synthesis
4.3 Voltage Controlled Oscillator (VCO)
The Voltage Controlled Oscillator (VCO) consists of the VCO/Buffer IC (VCOBIC, U4301), 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 (U4201) generates the required frequencies in 
both  transmit and receive modes. The TRB line (U4301 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 U4301 pin 12 (PRESC_OUT), via a low pass filter, to pin 32 of U4201 (PREIN).
A steering line voltage (VCTRL) between 3.0V and 10.0V at varactor diode CR4311 will tune the full 
TX frequency range (TXINJ) from 403 MHz to 470 MHz, and at varactor diodes CR4301, CR4302 
and CR4303 will tune the full RX frequency range (RXINJ) from 358 MHz to 425 MHz. The tank 
circuits uses the Hartley configuration for wider bandwidth. For the RX tank circuit, an external 
transistor Q4301 is used in conjunction with the internal transistor for better side-band noise.
 
Presc
RX
TXMatching
NetworkLow Pass
    Filter
Attenuator Pin8
Pin14
Pin10(U4201 Pin28)
VCC Buffers
TX RF Injection U4201 Pin 32 AUX3 (U4201 Pin 2)
Prescaler Out
Pin 12 Pin 19 Pin 20
      TX/RX/BS
Switching Network
U4301
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
(U4201 Pin 28)Rx-SW
Tx-SW
Vcc-Logic
(U4201 Pin 28) Steer Line 
Voltage 
(VCTRL)Pin13
Pin3TRB IN
LO RF INJECTION
Q4301
Q4332 
						

							UHF (403-470 MHz) Frequency Synthesis2-9
The external RX buffers (Q4332) are enabled by a high at U4201 pin 3 (AUX4) via transistor switch 
Q4333.  In TX mode the modulation signal (VCOMOD) from the LVFRAC-N synthesizer IC (U4201 
pin41) is applied modulation circuitry CR4321, R4321, R4322 and C4324, which modulates the TX 
VCO frequency via coupling capacitor C4321.  Varactor CR4321 is biased for linearity from VSF.
4.4 Synthesizer Operation
The complete synthesizer subsystem comprises mainly of low voltage FRAC-N (LVFRACN) IC, 
Reference Oscillator (crystal oscillator with temperature compensation), charge pump circuitry, loop 
filter circuitry and DC supply. The output signal PRESC_OUT of the VCOBIC (U4301 pin 12) is fed 
to pin 32 of U4201 (PREIN) via a low pass filter (C4229, L4225) which attenuates harmonics and 
provides the correct level to close the synthesizer loop.
The pre-scaler in the synthesizer (U4201) is basically a dual modulus pre-scaler with selectable 
divider ratios. This divider ratio of the pre-scaler is controlled by the loop divider, which in turn 
receives its inputs via the SRL. The output of the pre-scaler is applied to the loop divider. The output 
of the loop divider is connected to the phase detector, which compares the loop divider´s output 
signal with the reference signal.The reference signal is generated by dividing down the signal of the 
reference oscillator (Y4261 or Y4262).
The output signal of the phase detector is a pulsed DC signal which is routed to the charge pump. 
The charge pump outputs a current at pin 43 of U4201 (IOUT). The loop filter (which consists of 
R4221-R4223, C4221-C4225,L4221) transforms this current into a voltage that is applied to the 
varactor diodes CR4311 for transmit, CR4301, CR4302 & CR4303 for receive and alters the output 
frequency of the VCO .The current can be set to a value fixed in the LVFRAC-N IC or to a value 
determined by the currents flowing into BIAS 1 (U4201-40) or BIAS 2 (U4201-39). The currents are 
set by the value of R4251 or R4252 respectively. The selection of the three different bias sources is 
done by software programming.
To reduce synthesizer lock time when new frequency data has been loaded into the synthesizer the 
magnitude of the loop current is increased by enabling the IADAPT  (U4201-45) for a certain 
software programmable time (Adapt Mode). The adapt mode timer is started by a low to high 
transient of the CSX line. When the synthesizer is within the lock range the current is determined 
only by the resistors connected to BIAS 1, BIAS 2, or the internal current source. A settled 
synthesizer loop is indicated by a high level of signal LOCK (U4201-4). 
The LOCK (U4201-4) signal is routed to one of the µP´s ADCs input U101-56. From the voltage the 
µP determines whether LOCK  is active. In order to modulate the PLL the two spot modulation 
method is utilized. Via pin 10 (MODIN) on U4201 the audio signal is applied to both the A/D 
converter (low freq path) as well as the balance attenuator (high freq path). The A/D converter 
converts the low frequency analogue modulating signal into a digital code that is applied to the loop 
divider, thereby causing the carrier to deviate. The balance attenuator is used to adjust the VCO’s 
deviation sensitivity to high frequency modulating signals. The output of the balance attenuator is 
present at the MODOUT port (U4201-41) and connected to the VCO modulation diode CR4321 via 
R4321, C4325. 
						

							2-10UHF (403-470 MHz) Frequency Synthesis
THIS PAGE INTENTIONALLY LEFT BLANK 
						

							3-1
Section 3
TROUBLESHOOTING CHARTS
1.0 Troubleshooting Flow Chart for Receiver (Sheet 1 of 2)
Bad SINAD
Bad 20dB Quieting
No Recovered AudioSTART
Audio at 
pin 8 of 
U3101 ?Check Controller
(in the case of no audio)
OR ELSE go to “B” Ye s
No
Spray or inject 44.85MHz 
into XTAL Filter FL3101
Audio heard ?BYe s
No
Check 2nd LO 
(44.395MHz) at C3135 
LO present ?BYe s
 Check voltages on 
U3101Biasing OK ?
No
No
A
Ye s
Check Q3102  bias 
for faults
Replace Q3102
Go to B
Ye s
No
Check circuitry 
around U3101.
Replace 
U3101 if defect
Check circuitry around Y3101. 
Replace Y3101 if defectVoltages
 OK? 
						

							3-2Troubleshooting Flow Chart for Receiver
1.1Troubleshooting Flow Chart for Receiver (Sheet 2 of 2)
IF Signal at 
C3101?
No
RF 
Signal at 
T4051?
RF
Signal at 
C4015?
No
No
RF
Signal at 
C4025?
No or 
Check harmonic filter
L4491-L4493, C4492, J4401
and ant. switch
D4471, D4472, L4472.
Check filter between 
C4025 & C4009. 
Check tuning voltage 
at R4060.
Inject RF into J4401
Is
tuning voltage
OK?
No
Ye s
Check RF amp (Q4003) 
Stage.
Check filter between 
C4015 & T4051.
Ye s
Check T4051, T4052, 
D4051, R4052, L4008.
Ye s
1st LO level 
OK?
Locked?Ye s
Check FGU
Ye s
Trace IF signal 
from C3101 to 
Q3101. Check for 
bad XTAL filter.
No
Ye sIF
signal at Q3102 
collector?
Before replacing 
U3101, check 
U3101 voltages.
Ye s
Check for 
5VDC
Is 9V3 
present?
Check Supply Voltage 
circuitry. Check Q0681, 
U4211 and U0641.
No
No
No
Check U4501. 
Check varactor filter.
NoYe s
Ye s
Ye s
A
A
B
weak RFRF
Signal at 
C4009? 
						

							Troubleshooting Flow Chart for 25W Transmitter 3-3
2.0 Troubleshooting Flow Chart for 25W Transmitter (Sheet 1 of 3)
Current 
increase 
when 
keyed?
NO YES
START
Check if Pressure Pad closes S5440
Check Components between 
Q4441 and RF Output, 
Antenna Switch 
D4471,D4472,Q4472, 
VR3471,Q3471>500mA & 4A
1V
Short TP4403 to 
Ground
NO
YES
Voltage at 
TP4402 
rises?Check PA StagesNO
YES
PCIC U4501 
Pin 14 9.3V 
DC?Check 9.3 V Regulator 
U0641
NO
YESPCIC U4501 
Pin 16 >4V 
DCReplace PCIC U4501
NO
YESTP4404  
9.1V DC
If U4201 Pin 2 is high,  
replace PCIC 
U4501,otherwise 
check controller and 
FGU
YES
NOTP4403 
>0.5V DC?Replace PCIC U4501
Check Forward Power 
Sense Circuit (D4451)
Check Forward Power 
Sense Circuit (D4451)
NO
YESPCIC U4501 
Pin 5 > 1V 
DC?
Check Power Setting, 
Tuning & Components 
between PCIC Pin 5 
and ASFIC (U0221) 
Pin 4 before replacing 
ASFIC
No or too low Power when keyed 
						

							3-4 Troubleshooting Flow Chart for 25W Transmitter
2.1Troubleshooting Flow Chart for 25W Transmitter (Sheet 2 of 3)
Check PA Stages
No or too low Power when keyed
Measure DC Voltage at Pin 2 & 3 of U4401>6 YESDC Voltage 
at U4501 
Pin 23 =0?
2-6DC Voltage 
at U4402-1 
Pin 1?
YESPin 2
Voltage 0.62 
* Voltage at 
Pin 1?
If U4201 Pin 2 is high,  
replace PCIC
NOReplace U4401
YES NODC 
Voltage at 
U4402-1 Pin 
3 = 8.8V?
Check S4440, 
R4442 and R4443
YESPin 3 
Voltage 0.51 
* Voltage at 
Pin 1?
NOReplace U4401
6V
Check Components 
between U4402-2 Pin 7 
and Q4421. Check 
Resistive Network at 
Pins 5 & 6 before 
replacing Q4421
YESDC 
Voltage at 
U4402-2 Pin 5 

						

							Troubleshooting Flow Chart for 25W Transmitter 3-5
2.2Troubleshooting Flow Chart for 25W Transmitter (Sheet 3 of 3)
Check Final PA Stage
NO 0V
1-4VBias 2 DC 
Voltage at 
TP4406?
YESRF Voltage 
at TP4401 
>100mV?
YESRF Voltage 
U4401 Pin 6 
>3V?
Supply
Replace Q4441
Check FGU (U4301)
NOCheck Components 
between 
TP4401  &C4417
NO YESASFIC  
U0221 Pin 6 
1-4V DC?
Check Bias Tuning 
before replacing ASFIC 
U0221
Check Components 
between ASFIC and 
Q4441 before 
replacing Q4441
YESRF Voltage 
Q4421 Gate 
>1V?
NOCheck Components 
between 
C4417  & Q4421
YESRF Voltage 
Q4441 Gate 
>4V?
NOCheck Components 
between 
Q4421  & Q4441
Check Components 
between Q4441  & 
Antenna Connector
Voltage 
						

							3-6Troubleshooting Flow Chart for Synthesizer
3.0 Troubleshooting Flow Chart for Synthesizer
5V
 at pin 6 of 
D4201
Is
information
from
 µP U0101
correct
?
Is
U4201 Pin 47
at = 13VDC
?
Is
U4301 Pin 19
4.5 VDC in TX?  
(at VCO section)
?
Sta rt
Visual 
check of the 
Board
OK?Correct
Problem
Check 5V
Regulator
U4211
+5V
at U4201
Pins
13 & 30
?
Is
16.8MHz
Signal at U4201 
Pin 19
?
Check
Y4261 / Y4262 and 
associated parts
Are
signals
at Pins 14 &15 
of U4201
?
Check 
R4201Check C4381
Is
U4201
Pin 2  >4.5 VDC in 
Tx &