Vector-LP Radio Beacon Transmitter Technical Instruction Manual
Page
6-15
Section 6 Theory of Operation
Issue 1.1
6.4.4 Exciter Monitor/Generator
PWBs
See Figures SD-19 and SD-20. The exciter/
monitor/generator PWBs [A7 (exciter A) and
A10 (exciter B, if used)] perform the
following functions:
x
Use the press-to-talk input to select
between beacon and voice modes.
x
Monitor and control modulation depth
x
Selects the parameter, RF current or RF
voltage, to be applied to the remote
interface PWB for external monitoring.
x
Generate the appropriate tone frequency
x
Monitors tone and keyer operation
x
Monitors the forward power and controls
changeover and inhibit functions.
6.4.4.1 MICROCONTROLLER
Microcontroller U11 uses the SPI bus to
communicate with shift register U16 which
shifts out digital data used to control various
signals including changeover, shutdown, RF
off, and alarm. Watchdog timer IC U2 and
associated components generate a
Keying/
Misc Alarm
(J1-4) if the microcontroller falls
into an unknown state.
The clock for the microcontroller and the tone
oscillator is generated using Y1, U4:E and the
associated components.
The microcontroller (U11) continually
monitors its internal Flash and EEPROM
memory using checksums. If for some
reason, the checksum returns as invalid, the
microcontroller will detect the error and raise
a flag, resulting in the output power being
inhibit. U2 acts as a watchdog timer, if the
watchdog times out, the monitor fault will also
be raised, causing the output power to be
inhibited (via the control/display PWB). This
will guarantee that the U11 is always
operating as intended.
6.4.4.2 PRESS-TO-TALK
The input to U11:11 indicates to the exciter
monitor/generator PWB which mode of
operation it should be operating in. It will
react by adjusting the U16:1 that controls the
MUX U1:X.
6.4.4.3 MODULATION DEPTH
FUNCTIONS
Modulation depth of the beacon, voice and
beacon, and voice are controlled using the
digital pots 1, 2 and 3 of U10 respectively.
The levels of the pots in U10 are adjusted by
the microcontroller U11 over the SPI bus.
A selection between RF Monitor Voltage and
RF Monitor Current samples is made using
the MUX U14:C. CR9, U9:B and their
associated components RF detect the
selected RF monitor signal. The RF monitor
signal is then used to calculate the
modulation depth. The microcontroller (U11)
compares the average and peak levels of
the RF signal. The average value is detected
using U9:A and its associated components.
The peak level is detected using U9:C, CR7,
and their associated components.
6.4.4.4 TONE GENERATION
The keyer tone is generated using the DDS
IC U5. The microcontroller U11 sends an
SPI signal to U5 indicating the frequency of
the tone to generate. The tone is then
amplified using U8:C and its associated
components. The microcontroller (U11) then
controls keying by toggling the MUX U1:Z.
Correct operation of the keyer is monitored
by U8:A, U8:B, CR11, and CR12 and there
associated components. The analog
samples at U11:27 and U11:28 are
compared to the low threshold levels (set up
using the GUI) to determine if the keying
gate is opened or closed. If at any time the
keying gate is opened when it should be
closed or closed when it should be opened,
and alarm is flagged and output power is
inhibited (via the control/display PWB).
