Motorola Radius Cm200 Cm300 Pm400 Detailed 6881098c00 A Manual

Technical Specifications1-3
*Availability subject to the laws and regulations of individual countries.
Transmitter
Specification UHF2
Power Output1-25W
Conducted/Radiated 
Emissions:-36 dBm < 1 GHz 
-30 dBm > 1 GHz
Audio Response: (from 6 dB/
oct. Pre-Emphasis, 300 to 
3000Hz)
TIA603 and CEPT
Tx Audio Distortion < 3%
Modulation Limiting:±2.5 kHz @ 12.5 kHz
±4.0 kHz @ 20 kHz
±5.0 kHz @ 25 kHz
FM Hum and Noise: -35 [email protected] kHz
-40 dB@25 kHz
Receiver
Specification UHF2
Sensitivity (12 dB SINAD):0.35 μV @...

1-4 MODEL CHART AND TECHNICAL SPECIFICATIONS
Notes 

Chapter 2
THEORY OF OPERATION
1.0 Introduction
This Chapter provides a detailed theory of operation for the UHF circuits in the radio. Details of the 
theory of operation and trouble shooting for the the associated Controller circuits are included in this 
Section of the manual.
2.0 UHF (438-470 MHz) Receiver
2.1 Receiver Front-End
The received signal is applied to the radio’s antenna input connector and routed through the 
harmonic filter and antenna switch. The insertion loss of the harmonic...

2-2THEORY OF OPERATION
2.2 Receiver Back End
The IF signal from the crystal filter enters the IF amplifier which provides 20 dB of gain and feeds 
the IF IC at pin 1. The first IF signal at 44.85 MHz mixes with the second local oscillator (LO) at 
44.395 MHz to produce the second IF at 455 kHz. The second LO uses the external crystal Y301. 
The second IF signal is amplified and filtered by two external ceramic filters (FL303/FL302 for 
12.5 kHz channel spacing and FL304/FL301 for 25 kHz channel spacing)....

UHF Transmitter Power Amplifier (438-470 MHz) 2-3
power of the PA.Op-amp U103-3 monitors the drain current of U101 via resistor R122 and adjusts 
the bias voltage of U101.
In receive mode, the DC voltage from RX_EN line turns on Q101, which in turn switches off the 
biasing voltage to U101.
3.2 Power Controlled Driver Stage
The next stage is an LDMOS device (Q105) which provides a gain of 12 dB. This device requires a 
positive gate bias and a quiescent current flow for proper operation. The bias is set...

2-4THEORY OF OPERATION
3.6 Harmonic Filter
Inductors L111 and L113 along with capacitors C1011, C1023, C1020 and C1016 form a low-pass 
filter to attenuate harmonic energy coming from the transmitter. Resistor R150 along with L126 
drains any electrostatic charges 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 
to improve spurious response rejection.
3.7 Power Control
The output power...

UHF (438-470 MHz) Frequency Synthesis2-5
This oscillator is temperature compensated to an accuracy of +/-2.5 PPM from -30 to 60 degrees C. 
The temperature compensation scheme is implemented by an algorithm that uses five crystal 
parameters (four characterize the inverse Bechmann voltage curve and one for frequency accuracy 
of the reference oscillator at 25 degrees C). This algorithm is implemented by the LVFRAC-N (U200) 
at the power up of the radio.
TCXO Y200, along with its corresponding circuitry...

2-6THEORY OF OPERATION
4.3 Voltage Controlled Oscillator (VCO)
The Voltage Controlled Oscillator (VCO) consists of the VCO/Buffer IC (VCOBIC, U201), 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 the LVFRAC-N (U200) generate the required frequencies in both 
transmit and receive modes. The TRB line (U201, pin 19) determines which VCO and buffer is 
enabled (high being TX output at pin 10, low being RX...

UHF (438-470 MHz) Frequency Synthesis2-7
4.4 Synthesizer Operation
The synthesizer consists of a low voltage FRAC-N IC (LVFRAC-N), reference oscillator, charge 
pump circuits, loop filter circuit, and DC supply. The output signal (PRESC_OUT) of the VCOBIC 
(U201, pin 12) is fed to the PREIN, pin 32 of U200 via a low pass filter which attenuates harmonics 
and provides a correct input level to the LVFRAC-N in order to close the synthesizer loop.
The pre-scaler in the synthesizer (U200) is a dual modulus...

2-8THEORY OF OPERATION
5.0 Controller Theory of Operation
This section provides a detailed theory of operation for the radio and its components. The main 
radio is a single-board design, consisting of the transmitter, receiver, and controller circuits. A 
control head is connected by an extension cable. The control head contains LED indicators, a 
microphone connector, buttons, and speaker. 
In addition to the power cable and antenna cable, an accessory cable can be attached to a 
connector on the rear...