Motorola Radio Mcs2000 Vol 1 68p81083c20 A Manual

Controller Section Theory of Operation 7-19 capacitor between ASFIC pre-emphasis out U0200-C8 and ASFIC limiter in 
U0200-E8 AC couples the signal between ASFIC blocks and prevents the DC 
bias at the ASFIC output U0200-H8 from shifting when the ASFIC transmit 
circuits are powered up. The signal is then limited to prevent the transmitter 
from over deviating. The limited mic audio is then routed through a summer, 
used to add in signalling data, and then to a splatter Þlter to eliminate high 
frequency...

7-20 Controller Section Theory of Operation
Sub-audible Data 
(PL/DPL)Sub-audible data implies signalling whose bandwidth is below 300 Hz. PL and 
DPL waveforms are used for conventional operation and connect tones for 
trunked voice channel operation. The trunking connect tone is simply a PL 
tone at a higher deviation level than PL in a conventional system. Although it 
is referred to as Òsub-audible data,Ó the actual frequency spectrum of these 
waveforms may be as high as 250 Hz, which is audible to...

Controller Section Theory of Operation 7-21 these signals may also pass through a data pre-emphasis block in the ASFIC. 
Also these signalling schemes are based on sending a combination of 1200 Hz 
and 1800 Hz tones only. Microphone audio is muted during High Speed Data 
signalling.
Dual Tone 
Multiple 
Frequency (DTMF) 
DataDTMF data is a dual tone waveform used during phone interconnect 
operation. It is the same type of tones which are heard when using a ÒTouch 
ToneÓ telephone. 
There are seven...

7-22 Controller Section Theory of OperationSQ 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.
Audio Processing 
and Digital Volume 
ControlThe signal enters the controller section from the ZIF on DISC (IF1-3-2-1) and 
passes through RC Þlter R0245 and C0236 which Þlters out ZIF sampling 
noise. The signal is AC coupled by C0202 and enters the ASFIC via the PL IN 
pin U0200-J7. Inside...

Controller Section Theory of Operation 7-23 programmable attenuator whose level is set depending on the value of the 
volume control. Finally the Þltered audio signal passes through an output 
buffer within the ASFIC. The audio signal exits the ASFIC at RX AUDIO 
(U0200-J4).
The mP programs the attenuator, using the SPI BUS, based on SB9600 messages 
from the control head. The minimum /maximum settings of the attenuator 
are set by codeplug parameters. 
Since sub-audible signalling is summed with voice...

7-24 Controller Section Theory of Operation
Handset Audio
(Refer to schematic 
page 10-29 for 
reference)Certain hand held accessories have a speaker within them which require a 
different voltage level than that provided by U0203. For those devices RX HI 
is available at J0405-8.
The received audio from the output of the ASFICÕs digital volume attenuator 
is also routed to U0202 pin 6 where it is ampliÞed 15 dB; this is set by the 10k/
68k combination of R0238 and R0237. This signal is routed directly...

Controller Section Theory of Operation 7-25 follows a path identical to conventional receive audio, where it is Þltered (300-
3 kHz) and deemphasis.
Receive Signalling 
Circuits(Refer to Figure 7-5 for reference for the following sections)
The ASFIC (U0200) is used to Þlter and limit all received data. The data enters 
the ASFIC at U0200-J7. Inside U0200 the data is Þltered according to data type 
(HS or LS), then it is limited to a 0-5 V digital level. The MDC and trunking 
high speed data appear at...

7-26 Controller Section Theory of OperationThe allowable internal alert tones are 304, 608, 911, and 1823 Hz. 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 setting of the volume knob).
For external alert tones, the mP can generate any tone within the 100-3000 Hz 
audio band. This is accomplished by the mP generating a square wave which 
enters...

Controller Section Theory of Operation 7-27 dynamic range of a 12.5 kHz bandwidth channel as is obtained in a 25 kHz 
bandwidth channel.
The compressor raises low level signals and lowers high level signals. The 
compressor circuit produces a signal whose output voltage (U0250-F3) is based 
on the input voltage level (U0200-A6) of the signal. It is NOT a function of 
frequency (as is Preemphasis). The voltage transfer function is:
COMPOUT == SQRT[ 80*ASFICMICAUDOUT ]
Notice that 80 mV in yields 80 mV...

7-28 Controller Section Theory of OperationSome example levels are:
- 100 mV EXP IN ==  52 mV EXP OUT
- 191 mV EXP IN == 191 mV EXP OUT
- 250 mV EXP IN == 327 mV EXP OUT
Again this operation is NOT A FUNCTION OF FREQUENCY between 300 Hz 
and 3 kHz.
Hear Clear 
Routing of Data/
SignallingAll signalling for transmit enters the transmit stream after the Hear Clear 
Compressor and therefore does not pass through the compressor.
In receive, subaudible signalling PL/DPL goes through the Flutter Fighter 
along...