Motorola Gm1200e Detailled 68p64115b15 Manual

Transmit Audio Circuits
Introduction/Theory of Operation3.1-11
4.2 External Mic Path
The external microphone signal enters the radio on accessory connector J0400 pin 2 and connects 
to the standard microphone input through R0413. Components R0414 - R0416, C0413, C0414, 
C0417 are not used.
4.3 PTT Sensing and TX Audio Processing
Mic PTT coming from the Control Head via connector J101-4 is sensed by the mP U0101 pin 22. An 
external PTT can be generated by grounding pin 3 on the accessory connector. When...

Transmit Signalling Circuits
3.1-12Introduction/Theory of Operation
5.0 Transmit Signalling Circuits
Refer to Figure 3-2 for reference for the following sections. From a hardware point of view, there are 
three types of signalling:
1.Sub-audible data (PL/DPL/Connect Tone) that gets summed with transmit voice or signalling,
2.DTMF data for telephone communication in trunked and conventional systems, and
3.Audible signalling including Select 5, MPT-1327, MDC, High speed Trunking.
NOTE: All three types are...

Transmit Signalling Circuits
Introduction/Theory of Operation3.1-13
5.2 High Speed Data
High speed data refers to the 3600 baud data waveforms, known as Inbound Signalling Words 
(ISWs) used in a trunking system for high speed communication between the central controller and 
the radio. To generate an ISW, the mP first programs the ASFIC (U0201) to the proper filter and gain 
settings. It then begins strobing U0201-G1 (TRK CLK IN) with a pulse when the data is supposed to 
change states. U0201’s 5-3-2...

Receive Audio Circuits
3.1-14Introduction/Theory of Operation
6.0 Receive Audio Circuits
Refer to Figure 3-3 for reference for the following sections.
Figure 3-3  Receive Audio Paths.
6.1 Squelch Detect
The radio’s RF circuits are constantly producing an output at the discriminator U5201-28 (UHF) / 
U5201-28 (VHF) / U2201-28 (MB). This signal (DET AUDIO) is routed to the ASFIC’s squelch detect 
circuitry input SQ IN (U0201-H7). All of the squelch detect circuitry is contained within the ASFIC. 
Therefore...

Receive Audio Circuits
Introduction/Theory of Operation3.1-15
CH ACT is routed to the mP pin 40 while SQ DET adds up with LOCK DET, weighted by resistors 
R0113, R0114, and is routed to one of the mP´s ADC inputs U0101-43. From the voltage weighted 
by the resistors the mP determines whether SQ DET, LOCK DET or both are active.
SQ DET is used to determine all audio mute/unmute decisions except for Conventional Scan. In this 
case CH ACT is a pre-indicator as it occurs slightly faster than SQ DET.
6.2...

Receive Audio Circuits
3.1-16Introduction/Theory of Operation
The audio PA is enabled via AUDIO PA ENABLE signal from the ASFIC (U0201-B5). When the base 
of Q0401 is low, the transistor is off and U0401-8 is high, using pull up resistor R0406, and the Audio 
PA is ON. The voltage at U0401-8 must be above 8.5VDC to properly enable the device. If the 
voltage is between 3.3 and 6.4V, the device will be active but has its input (U0401-1/9) off. This is a 
mute condition which is not employed in this radio...

Receive Signalling Circuits
Introduction/Theory of Operation3.1-17
7.0 Receive Signalling Circuits
Refer to Figure 3-4 for reference for the following sections.
Figure 3-4  Receive Signalling Path.
7.1 Sub-audible Data (PL/DPL) and High Speed Data Decoder
The ASFIC (U0201) is used to filter and limit all received data. The data enters the ASFIC at U0201-
J7. Inside U0201 the data is filtered according to data type (HS or LS), then it is limited to a 0-5V 
digital level. The MDC and trunking high speed data...

Receiver Front-End
3.1-18Introduction/Theory of Operation
The allowable internal alert tones are 304, 608, 911, and 1823Hz. In this case a code contained 
within the SPI BUS load to the ASFIC sets up the path and determines the tone frequency, and at 
what volume level to generate the tone. (It does not have to be related to the voice volume setting).
For external alert tones, the mP can generate any tone within the 100-3000Hz audio band. This is 
accomplished by the mP generating a square wave which...

Transmitter Power Amplifier (PA) 5-25W
Introduction/Theory of Operation3.1-19
8.2 Mixer and Intermediate Frequency (IF) Section
The signal coming from the front-end is converted to the first IF (45.1 MHz) using a double balanced 
schottky diode mixer (D5401). Its ports are matched for incoming RF signal conversion to the 
45.1MHz IF using low side injection. The injection signal (VCO MIXER) coming from the mixer buffer 
(Q5771) is filtered by the lowpass consisting of (L5403, L5404, C5401 - C5403) and has a...

Transmitter Power Amplifier (PA) 5-25W
3.1-20Introduction/Theory of Operation
The collector current of Q5510 causes a voltage drop across the resistors R5623 and R5624. 
Transistor Q5612 adjusts the voltage drop across R5621 controlled through the PA control line 
(PWR CNTL). The current source Q5621 adjusts the collector current of Q5510 by modifying its 
base voltage via (R5502, L5501) until the voltage drop across R5623 and R5624 plus V
BE (0.6V) 
equals the voltage drop across R5621 plus V
BE (0.6V)...