Motorola Cm Radio Midband 66 88mhz Information Manual

Midband Transmitter Power Amplifier (66-88 MHz) 2-3
For a given control voltage input on VCNTR1, Op-amp U103-3 monitors the drain current of U101 
via resistor R122 and adjusts the bias voltage of U101 accordingly.
In receive mode, the DC voltage from RX_EN line turns on Q101, grounding VCNTR1, 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 up to 15dB. This device 
requires a positive gate bias...

2-4THEORY OF OPERATION
3.6 Harmonic Filter
Inductors L1511, L1512, L1513 and L1515 along with capacitors C1518 to C1523, C1528, C1532 to 
C1535, C1537 to C1539 and C1542 form a 9-element elliptical low-pass filter to attenuate harmonic 
energy coming from the transmitter. Resistor R152 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...

Midband (66-88MHz) Frequency Synthesis2-5
The method of temperature compensation is to apply an inverse Bechmann voltage curve, which 
matches the crystal’s Bechmann curve to a varactor that constantly shifts the oscillator back on 
frequency. The crystal vendor characterizes the crystal over a specified temperature range and 
codes this information into a bar code that is printed on the crystal package. In production, this 
crystal code is read via a 2-dimensional bar code reader and the parameters are...

2-6THEORY OF OPERATION
4.3 Voltage Controlled Oscillator (VCO)
The Voltage Controlled Oscillator (VCO) uses 2 colpitts oscillators, FET Q2741 for transmit and FET 
Q2751 for receive. The appropriate oscillator is switched on or off by LVFRAC-N IC output AUX3 
(U200-2) using transistors Q2742 and Q2752. In RX mode AUX3 is nearly at ground level and 
Q2742 enables a current flow from the source of FET Q2751 while Q2752 is switched off. In TX 
mode AUX3 is about 3.3V DC and Q2742 is switched off. Q2752 is...

Midband (66-88MHz) 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 from the pre-scaler buffer (Q2790) 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 pre-scaler...

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...