Motorola Gm1200e Detailled 68p64115b15 Manual

Transmitter Power Amplifier (PA) 5-25W
Introduction/Theory of Operation3.1-21
9.4 Antenna Switch
The antenna switch is switched synchronously with the K9V1 voltage and feeds either the antenna 
signal coming through the harmonic filter to the receiver or the transmitter signal coming from the PA 
to the antenna via the harmonic filter.
In transmit mode, this K9V1 voltage is high and biases Q5520 and along with the RF signal from 
Q5510 allows a collector current to be drawn. The collector current of Q5520...

Transmitter Power Amplifier (PA) 5-25W
3.1-22Introduction/Theory of Operation
The ALC loop regulates power by adjusting the PA control line PWR CNTL to keep the forward 
power voltage PWR DETECT at a constant level.
Opamp U0701-2 and resistors R0701 to R0703 and R0731 subtract the negative PWR DETECT 
voltage from the PA PWR SET D/A output U0731 pin 2. The result is connected to opamp inverting 
input U0701-4 pin 9 which is compared with a 4.6 volt reference VAG present at noninverting input 
U0701-4 pin...

Frequency Synthesis
Introduction/Theory of Operation3.1-23
10.0 Frequency Synthesis
The complete synthesizer subsystem consists of the Reference Oscillator (Y5701 or U5702), the 
Fractional-N synthesizer (U5701), the Voltage Controlled Oscillator (Q5741), the RX and TX buffer 
stages (Q5751, Q5771, Q5781) and the feedback amplifier (Q5791).
10.1 Reference Oscillator
The Reference Oscillator (Y5702) contains a temperature compensated crystal oscillator with a 
frequency of 16.8 MHz. An Analogue to Digital...

Frequency Synthesis
3.1-24Introduction/Theory of Operation
10.3 Voltage Controlled Oscillator (VCO)
The Voltage Controlled Oscillator (VCO) is formed by the colpitts oscillator FET Q5741. Q5741 
draws a drain current of 12 mA from the FRAC-N IC super filter output. The oscillator frequency is 
half of the desired frequency and mainly determined by L5743, C5742, C5743, C5745 - C5748 and 
varactor diodes D5741 / D5742. Diode D5743 controls the amplitude of the oscillator.
A balanced frequency doubler T5751,...

Receiver Front-End
Introduction/Theory of Operation3.1-25
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 line (U5701-31) for a certain 
software programmable time (Adapt Mode). The adapt mode timer is started by a low to high 
transient of the FRACN CE line. When the synthesizer is within the lock range the current is 
determined only by the resistors connected to CPBIAS 1, CPBIAS 2, or...

Transmitter Power Amplifier (PA) 5-25W
3.1-26Introduction/Theory of Operation
A second two pole varactor tuned bandpass filter provides additional filtering to the amplified signal. 
The dual varactor diode D3304 is controlled by the same signal which controls the pre-selector filter.
If the radio is configured for a base station application, R3318 is not placed and TP3301 and TP3302 
are shorted.
11.2 Mixer and Intermediate Frequency (IF) Section
The signal coming from the front-end is converted to the first...

Transmitter Power Amplifier (PA) 5-25W
Introduction/Theory of Operation3.1-27
12.1 Power Controlled Stage
The first stage (Q3511) amplifies the RF signal from the VCO (line EXCITER PA) and controls the 
output power of the PA. The output power of the transistor Q3511 is proportional to its collector 
current which is adjusted by a voltage controlled current source consisting of Q3641, (Q3643-T3 
only) and Q3642. The current of the whole stage is drawn from the RX-TX Switch through coil 
L3652.
Transistor...

Transmitter Power Amplifier (PA) 5-25W
3.1-28Introduction/Theory of Operation
12.4 Antenna Switch
The antenna switch is switched synchronously with the K9V1 voltage along with the voltage PWR 
CNTL signal and feeds either the antenna signal coming through the harmonic filter to the receiver 
or the transmitter signal coming from the PA to the antenna via the harmonic filter.
In transmit mode, this PWR CNTL is above 1 V and biases Q3511 through Q3641 and Q3642 to 
allow a collector current to be drawn. The...

Transmitter Power Amplifier (PA) 5-25W
Introduction/Theory of Operation3.1-29
The ALC loop regulates power by adjusting the PA control line PWR CNTL to keep the forward 
power voltage PWR DETECT at a constant level.
Opamp U0701-2 and resistors R0701 to R0703 and R0731 subtract the negative PWR DETECT 
voltage from the PA PWR SET D/A output U0731 pin 2. The result is connected to opamp inverting 
input U0701-4 pin 9 which is compared with a 4.6 volt reference VAG present at noninverting input 
U0701-4 pin...

Frequency Synthesis
3.1-30Introduction/Theory of Operation
13.0 Frequency Synthesis 
The complete synthesizer subsystem consists of the Reference Oscillator (Y3701 or Y3702), the 
Fractional-N synthesizer (U3701), the Voltage Controlled Oscillator (Q3741, Q3751), the RX and TX 
buffer stages (Q3760, Q3770, Q3780) and the feedback amplifier (Q3790).
13.1 Reference Oscillator
The Reference Oscillator (Y3702) contains a temperature compensated crystal oscillator with a 
frequency of 16.8 MHz. An Analogue to...