GPH-CMD VHF Radio Theory of Operation
BK RADIO Page 4-7
G. VCO Coarse Tune Adaptive Filter
R26 and C50 form a low cutoff frequency pole to filter out noise on the Coarse Tune line to the
VCO. When changing to a new frequency that requires a different Coarse Tune voltage, switch
U11 is closed for a short time to allow the voltage on C50 to change to the new value rapidly.
H. 3.0V Regulator
U12 provides a low noise regulated 3.0V supply that powers the TCXO Reference Y1 and all
sections of the synthesizer IC U6 except the charge pump phase detector and frequency steering
circuit.
I. 4.5V Regulator
U13 provides a low noise regulated 4.5V supply that powers the charge pump phase detector and
frequency steering sections of the synthesizer IC U6.
4.3.4 SYSTEMS AREA
A variety of functions are included in the Systems area.
A 3.3V precision voltage regulator provides power to the Microprocessor and several other digital ICs in
the radio. A 5.0V precision voltage regulator serves as the primary regulated analog supply in the radio.
The 7.0V regulator is used to supply the VCO, VCO Buffer and Synthesizer Buffer. An output signal from
the 7.0V regulator will alert the processor if the battery voltage falls too low for proper operation of this
regulator. A -15V switching regulator generates the negative supply needed to produce the negative
VCO Coarse Tune and Receiver Front End Tune/Transmitter Power Set signals.
Several special Transmitter features are implemented by the Microprocessor. These include Repeater
Talk-Around, Busy Channel Lockout, DTMF Control, ANI Control, Sub-audible Code Guard Control, and
Transmit Time-Out Timer.
Receive Mode special features provided by the Microprocessor include Channel Scan, Dual Priority
Scan, Scan Hold Timer, and Battery Saver.
Other functions performed by the Microprocessor include: storing and retrieving hardware alignment and
channel information, tuning the Receiver Front End, setting the Transmit power level, setting the squelch
gain, interpreting the user switches, generating display information, and implementing remote and
keypad programming modes.
A. Microprocessor
The Microprocessor U1 receives inputs from user switches and controls radio functions such as
adjusting the Transmitter deviation, tuning the Receiver, setting transmit power, time-out functions,
etc.
B. EEPROM
The EEPROM U7 stores channel information and hardware compensation values.
C. VCO Coarse Tune
D/A converter U2 and amplifier U10-A allow the Microprocessor to set the VCO Coarse Tune
voltage to any value within the range of 0V to -12V.
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