TM 11-5821-333-30
2-11. TRANSMIT AUDIO/DATA SIGNAL PATH
The transmit audio signal, data signal, and PTT are processed in the interface module and switching module. See
Figure FO-4.
The interface module furnishes speech processing for audio signals. Processing includes pre-emphasis and
compression. The compressor output goes three places: 1) sidetone to receive audio circuits, 2) SC/PT audio
to the switching module, and 3) FH/PT audio to the ECCM module. The SC/PT audio is summed with 150-Hz
squelch tone. The FH/PT audio is band limited by a low pass filter.
During retransmit (RXMT) operation (para 2-18), the PT audio is disconnected and RXMT audio enters the audio
path by way of a summing circuit. From that point the RXMT audio is processed identical to the PT audio.
The interface module has a buffer amplifier for X-mode signals and detect/debounce circuits for the PTT signal,
XMT X-MODE signals are cipher-text (CT) audio signals or data signals. X-MODE SEL enables the digital path in
the switching mode.
The switching module contains digital and analog switches which route digital and analog signals under supervi-
sion of the control module. All audio/data signals pass through a final amplifier and are routed to the amplifier-os-
cillator for modulation of the FM carrier. In the FH mode, FH/PT AUDIO or BS DATA is sent to the ECCM module
for interleaving. The FH DATA is returned to the switching module to continue the digital signal path.
2-12. LOCAL CONTROL OPERATION
The local control panel includes:
l rt controls and display
l serial data interface with control module
l serial data interface with optional remote control unit
See Figure FO-5. The microprocessor reads instructions stored in ROM and controls operation of the rest of the
local control panel. A RAM is used to store data for transfer to the rt circuits or display.
Most rt control information is sent through the level shifter to the rt control module. This information includes
FUNCTION switch position, MODE switch position, PRESET switch position, and keyboard data. The level shifter
changes signals from the 5 V dc logic of the local control panel to the 6.75 V dc logic of the rt. Switch data is sent
on the REM DATA line accompanied by sixteen 640-Hz clock pulses on the REM 24 CLOCK line and one pulse on
the REM 24 STROBE line. Keyboard data is sent on the REM DATA line accompanied by eight 640-Hz clock pulses
on the REM 8 CLOCK line and one pulse on the REM 8 STROBE line.
The 115 V ac is used for display lighting and front panel lighting.
Display data is provided by the rt control module to the control panel DMA control and buffer. The DMA control
and buffer changes serial data from the rt to parallel data for the microprocessor. The display data is received on
the SERIAL DATA line and is accompanied by the DISP CLOCK.
The IFM PWR A and IFM PWR B signals are derived from the IFM RF PWR switch setting and are used to control the
output power of the optional IFM power amplifier. The signals are connected from the decoder timer and DMA
control and buffer to buffers on the rt interface module.
The decoder timer also provides STBY, STBY RESET-N, HB ON, and HB OFF signals for use by the rt power supply
(para2-5).
Interface with an optional remote control unit is through the drivers/receivers. Eight-bit serial data words are sent
in either direction on the DATA (+) and DATA (-) lines accompanied by a clock on the CLOCK (+) and CLOCK (-)
lines. The DATA DIRECTION signal from the control unit determines whether the data is an input or output.
A reset circuit generates a negative reset pulse at power turn-on. This is used to start the microprocessor at the
correct place in its program. A negative reset pulse is also generated whenever the TAKE CONTROL switch
changes. This starts the microprocessor at the beginning of its program whenever relinquishing or taking control
of the rt. The reset circuit also holds the reset negative when LV RESET is present. LV RESET is present when the
+28V line drops to about +18V.LV RESET is supplied by the interface module.
2-11
