Guardian G25AMK005, Техническое руководство

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2-16 G U A R D I A N V H F 1 1 0 W M O B I L E
2.6.6 PA ON/OFF Control (Bypass Mode)
It is possible to operate the system not utilizing the PA (PA in by pass mode.) This is done by turning on control
head on with the PTT depressed. An orange TX light indicates to the user that he is operating in by pass mode. In
this mode, output power is about 1dB lower that the nominal levels delivered from the transceiver, as indicated in
the table above. In normal mode, Q16 conducts at start-up, causing Q14 to conduct, which keeps Q15 off. When
using this mode, Q16 conducts in the reverse direction, Q14 remains off and Q15 conducts, which prevents bias
voltage from being sent to the RF power amplifier.
2.6.7 RF Power Indication
Operational amplifier U3A forces the output control voltage at Q8-E to be equal to that at U3-3. After high power
transmit is detected at the PA output. The RF PA test circuit forces additional current back into this line. The op-
amp loop holds the voltage at the input level, so the additional current is forced out Q8-C and through R44. This
forces Q9 to conduct and sink additional current from the LED_TX. The LED_TX turns off the green light. When
the unit is in bypass (low power) mode the Tx lamplights orange because the red and the green LED’s are on.
2.6.8 Audio Board Block Diagram
Audio Block diagram
RFI filter&
transient
protection
on off switch
voltage
ragulator
7.8volts
7.8volts
switched
internal
audio amplifier
external
audio amplifier
audio in
power level
voltage
converter
RF&DC
combiner
RF IN
RF &control out/in
D
B
9
D
B
25
J2 - IDC 20 pin J3 - IDC 20 pin
PA on off
control
Switch PTT
7.8volts
switched
input voltage
audio out p
audio out n
audio out p
audio out n
j
4
power level input
Figure 2-4: Audio Board Block Diagram