Motorola Cm Radio Vhf2 Information Manual

VHF Transmitter Power Amplifier (146-174 MHz) 2-3
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 12dB. This device requires a 
positive gate bias and a quiescent current flow for proper operation. The bias is set during transmit...

2-4THEORY OF OPERATION
3.6 Harmonic Filter
Inductors L111, L112 and L113 along with capacitors C1011, C1024, C1025, C1022, C1020, C1016, 
C1017 and C1026 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....

VHF (146-174MHz) 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 amplifier, and the modulation circuitry.
Figure 2-4VHF 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 output...

VHF (146-174MHz) 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...

Controller Theory of Operation2-9
The DC voltage applied to connector P2 supplies power directly to the following circuitry:

Electronic on/off control

RF power amplifier

12 volts P-cH FET -U514

9.3 volt regulator

Audio PA
Figure 2-6DC Power Distribution Block Diagram
Regulator U501 is used to generate the 9.3 volts required by some audio circuits, the RF circuitry 
and power control circuitry. Input and output capacitors are used to reduce high frequency noise. 
Resistors R5001 / R5081 set the...

2-10THEORY OF OPERATION
Voltage regulator U503 provides 5V for the RF circuits. Input and output capacitors are used to 
reduce the high frequency noise and provide proper operation during battery transients.
VSTBY is used only for CM360 5-tone radios.
The voltage VSTBY, which is derived directly from the supply voltage by components R5103 and 
VR502, is used to buffer the internal RAM. Capacitor C5120 allows the battery voltage to be 
disconnected for a couple of seconds without losing RAM parameters....

Controller Theory of Operation2-11
5.3.3 Emergency Mode
The emergency switch (P1 pin 9), when engaged, grounds the base of Q506 via EMERGENCY 
_ACCES_CONN. This switches Q506 to off and consequently resistor R5020 pulls the collector of 
Q506 and the base of Q506 to levels above 2 volts. Transistor Q502 switches on and pulls U501 
pin2 to ground level, thus turning ON the radio. When the emergency switch is released R5030 pulls 
the base of Q506 up to 0.6 volts. This causes the collector of transistor...

2-12THEORY OF OPERATION
5.5 Serial Peripheral Interface (SPI)
The µP communicates to many of the IC’s through its SPI port. This port consists of SPI TRANSMIT 
DATA (MOSI) (U403-pin100), SPI RECEIVE DATA (MISO) (U403-pin 99), SPI CLK (U0403-pin1) 
and chip select lines going to the various IC’s, connected on the SPI PORT (BUS). This BUS is a 
synchronous bus, in that the timing clock signal CLK is sent while SPI data (SPI TRANSMIT DATA 
or SPI RECEIVE DATA) is sent. Therefore, whenever there is activity...