Technical Description 4-16 X-2 Technical Service Manual
Publication No: 15-02047
Transmit reflected power
The transmit reflected power detector output from D2 (REF-PWR), on the
PA assembly, is applied via resistor divider R411 and R413 to pin 3 of
IC403.
Tune Pass/Fail
The microcontroller compares the forward and reflected power when in the
tune mode and provides a pass or fail indication on completion of the tune
cycle. A pass tone indicates a VSWR of < 3:1 and a fail tone indicates a
VSWR of > 3:1.
4.5.8 Microcontroller Reset
104-02907 Sheet 3
The reset line to the microcontroller IC403 pin 18 is normally held to 5 V.
Reset circuit IC304/B
[G4]
and its associated components monitor the supply
voltage on A line. When the supply falls below 8.7 V, the output of IC304/B
applies a low via D403 to the reset pin 18.
To eliminate jitter on the reset line, resistor R417 provides a hysteresis to the
reset network. This prevents the output of IC403 from going high until the
supply has risen above 9 V.
4.6 PA and Filters
104-02908
Power Supply
The drivers and output stages (including part of the output bias circuit) are
permanently connected to the supply voltage when the Power On relay K8 is
energised. Power to the rest of the PA is switched by V2
[D9]
when PTT is
enabled.
Filter Selection
The selection of the PA filters and the operation of the PTT are controlled by
the microcontroller. Serial data from the microcontroller IC403 is applied to
IC1
[C4]
(serial data input/8 bit output driver).
Depending on the channel frequency, the microcontroller selects the
appropriate filter by grounding one of the output pins 14 to 18. In addition,
pin 11 will be grounded or set high depending on whether antenna 1 or 2 is
required (J1 or J2).
To Next Page
Loading...
Need help?
General
