Motorola Cp200 Detailed 6880309n62 C Manual

6880309N62-CJune, 2005
465-495 MHz UHF Theory Of Operation: UHF Transmitter 10-3
10.3 UHF Transmitter
The UHF transmitter covers the range of 465-495 MHz. Depending on model, the output power of the 
transmitter is either switchable on a per-channel basis between high power (4 watts) and low power 
(1 watt), or is factory preset to 2 watts. The transmitter is divided into four major blocks as shown in 
Figure 10-2.
• Power Amplifier
• Harmonic Filter 
• Antenna Matching Network
• Power Control.
Figure...

June, 20056880309N62-C
10-4465-495 MHz UHF Theory Of Operation: UHF Frequency Generation Circuitry
10.3.4 Antenna Matching Network
The harmonic filter presents a 50Ω impedance to antenna jack J140. A matching network, made up of 
C140-C141 and L140, is used to match the antenna impedance to the harmonic filter. This optimizes 
the performance of the transmitter and receiver into the impedance presented by the antenna, 
significantly improving the antennas efficiency.
10.3.5 Power Control
The power...

6880309N62-CJune, 2005
465-495 MHz UHF Theory Of Operation: UHF Frequency Generation Circuitry 10-5
SPI_CLK, and SYNTH_CS (chip select) lines (U409 pins 100, 1 and 47 respectively). A logic high 
(3 V) from U201 pin 4 indicates to the microprocessor that the synthesizer is locked.
Figure 10-3.  UHF Frequency Generation Unit Block Diagram
Transmit modulation from the ASFICcmp (U451 pin 40) is applied to U201 pin 10 (MOD_IN). An 
electronic attenuator in the ASFICcmp adjusts overall transmitter deviation...

June, 20056880309N62-C
10-6465-495 MHz UHF Theory Of Operation: UHF Frequency Generation Circuitry
One of the auxiliary outputs of the synthesizer IC (AUX3, U201 pin 2) provides the TRB signal which 
determines the operating mode of the VCO, either receive or transmit.
Figure 10-4.  UHF Synthesizer Block Diagram
10.4.2 Voltage Controlled Oscillator (VCO)
The VCOBIC (U251), shown in Figure 10-5, in conjunction with the Fractional-N synthesizer (U201) 
generates RF in both the receive and the transmit...

6880309N62-CJune, 2005
465-495 MHz UHF Theory Of Operation: UHF Frequency Generation Circuitry 10-7
C267, and varactor D261. High-port audio modulation from the synthesizer IC is applied as 
VCO_MOD to varactor D262 which modulates the transmit VCO.
Figure 10-5.  UHF VCO Block Diagram
Presc
RX
TX
Matching 
Network Pin 8
Pin 14
Pin 103V (U330 Pin 5)
VCC BuffersU201 Pin 32 AUX3 (U201 Pin 2)
Prescaler Out
Pin 12 Pin 19 Pin 20
TX/RX/BS
Switching Network
U251
VCOBIC
Rx Active
Bias
Tx Active
Bias
Pin 2
Rx-I...

June, 20056880309N62-C
Notes:
10-8465-495 MHz UHF Theory Of Operation: UHF Frequency Generation Circuitry 

Chapter 11 UHF Troubleshooting Tables
11.1 Troubleshooting Table for Receiver
Table 11-1.  Troubleshooting Table for Receiver 
Symptom Possible Causes Procedure Corrective Action
Radio Dead (no 
turn-on beep, no 
LED indication)1. Battery dead or defec-
tive.Substitute known good battery or 
battery eliminator.Charge or replace battery.
2. Defective batery con-
tacts.Inspect battery contacts for corrosion 
or bent terminals.Clean/repair/replace J301.
3. Blown fuseCheck voltage on each side of fuse. 
If...

June, 20056880309N62-C
11-2UHF Troubleshooting Tables: Troubleshooting Table for Receiver
No Audio
1. Synthesizer out of lockVerify U201-4 is at 3V dc.Troubleshoot synthesizer/VCO 
circuits.
2. Defective IFIC Verify audio is present  at U51-8. Check Q70, Y70, U51.
3. RX audio buffer faultVerify audio is present  at U451-2.Check U510 and associated 
parts.
4. ASFIC fault Verify audio is present at U451-41. 
Verify U451-14 is high.Check squelch setting, PL/DPL 
programming. Troubleshoot/
replace U451.
5....

6880309N62-CJune, 2005
UHF Troubleshooting Tables: Troubleshooting Table for Synthesizer 11-3
11.2 Troubleshooting Table for Synthesizer
Table 11-2.  Troubleshooting Table for Synthesizer 
Symptom Possible Causes Procedure Corrective Action
Synthesizer Out of 
Lock (RX mode 
only)1. VCO faultVerify oscillator is working, check RF 
level at U251-10 per schematic.
Check dc voltages at U251 pin 2 
through 6 and 10 per 
Table 11-4.
Verify steering line voltage is 
between ~3V and 10V.
Check VCO tank...

June, 20056880309N62-C
11-4UHF Troubleshooting Tables: Troubleshooting Table for Transmitter
11.3 Troubleshooting Table for Transmitter
Table 11-3.  Troubleshooting Table for Transmitter 
Symptom Possible Causes Procedure Corrective Action
No Transmit (no TX 
LED indication)1. PTT switch defective.Verify U401-71 goes low when PTT 
is pressed.Replace PTT switch S441.
2. EXT MIC PTT fault Verify U401-72 goes low when J471-
4 is grounded.Check/replace Q470, L471 etc.
No Transmit (TX 
LED indication OK)
1....