RED PT500-2, Руководство по обслуживанию

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PT500-2 Service Manual
23
The oscillation frequency of VCO is compared with reference frequency to produce error
signal after divided by PFD in IC1. The error signal is filtered by low pass filter before
changing the VCO frequency to the set value in VCO (it is locking).
N=F
VCO
/F
R
N
：
Division Frequency
F
VCO
：
VCO Oscillation Frequency
F
R
：
Reference Frequency
Lock lost detection: When PLL is out of lock, IC pin14 will output low level signal to MCU
，
and then MCU prohibit transmitter from transmitting with a warning tone.
Q8, the power filter, can provide PLL with more purified power to reduce the noise of
frequency synthesizer.
5.5 Voice Circuit
The station is equipped with Voice Prompt Function, which is very useful during night or
under dark condition.
The speaker will voice the current channel number when changing the channel every time
because of the voice memory chip (IC401), which stores channel voice prompts.
5.6 Power Supply:
The station use lithium battery (7.4V, 1300mAh), while transmitter amplifier circuit (Q105
Q107) and receiver audio amplifier (IC302) use battery directly for power supply, and other
circuits use regulated voltage (5V and 3V).
IC404:micro-power voltage stabilizer of 3V LDO, provides power (3V) of heavy current for
the station together with Q10 and Q30.
IC902:5V LDO
Q405: 5T switch (controlled by MCU)
5T: supply power for the front end of transmitter
Q408: 5R switch (controlled by MCU)
5R: supply power for the units such as RF amplification, mixing, IF processing and
audio signal processing.
Q910: 5C switch (controlled by MCU)
5C: the power (5V), controlled by power-down mode, is the supply power of frequency
synthesizer.