Control/Loader Board; Hardware Options - Ritron DTX-165-0 Maintenance And Operating Manual

8.2

CONTROL/LOADER BOARD

The control/loader board is responsible for controlling the operation of the RF board and for
processing the audio input and output signals to and from the RF board and to and from the
outside.
Audio Chain
The audio processing, both transmit and receive, is handled by the audio Codec IC, U302 and the
DSP microcontroller U301. These devices handle pre-emphasis, modulation limiting, and
lowpass filtering on transmit as well as de-emphasis and filtering on receive.
In transmit, the audio inputs are routed to the Codec IC. This IC has internal analog to digital
converters which convert the analog input to a digital data stream. This data stream is sent to the
DSP processor where the signal is adjusted in level, filtered, limited, and filtered again. The
output digital signal is sent back to the Codec IC where digital to analog converters convert the
signal back to analog for routing to the RF board for FM modulation.
In receive, the raw discriminator audio from the RF board is passed to the Codec and is
converted to a digital signal. The digital signal is processed by the DSP processor for level and
frequency response and sent back to the Codec. The Codec converts the signal back to analog
where it is sent to the I/O connector.
Other Analog Functions
To supply the proper voltages for the two boards, various voltage regulators are used. U310 is
used to produce +7.5 VDC for the RF board. U308 and U309 are used to supply +5 VDC and
+3.3 VDC for the control/loader board.
9

HARDWARE OPTIONS

The DTX is setup at the factory in a configuration that should be acceptable for most users. The
most common changes required are effected through the programmer without removing the cover
from the unit. There are, however, a number of component jumper changes which can be made
which may result in more satisfactory integration in a data system. These changes require the
soldering and unsoldering of SMD components and should be undertaken only by qualified
service personnel. Refer to the PCB component locator and schematic diagrams as needed.
9.1 CONTROL/LOADER BOARD OPTIONS
9.1.1 AUX OUT COUPLING
The AUX OUT output is normally AC coupled through C372. If DC coupling is desired, an 0805
size SMD zero ohm jumper resistor (RITRON P/N 47100000) must be soldered in the location of
C372. (In lieu of a zero ohm jumper, a small piece of wire may be carefully soldered between the
pads.) The AUX OUT DC level then becomes nominally 1.67 volts.
9.1.2 AUX IN COUPLING
The AUX IN input is normally AC coupled through C352. DC coupling is possible, however, the
carrier frequency of the unit would then become directly affected by the DC voltage present. If
DC coupling is desired, C352 must be removed and an 0805 size SMD zero ohm jumper resistor
(RITRON P/N 47100000) must be soldered in the C352 location. The DC voltage should be 2.5
volts nominal and very well regulated. Note: The FCC Type Acceptance obtained by RITRON
is invalid once this modification is made. The user is responsible for obtaining type
acceptance in a configuration which includes the device which is connected to the AUX IN
input.