User's 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 DB-
15 Connector, J301.
Audio Chain
The audio processing, both transmit and receive, is handled by the audio processing IC, U302
and the 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 input is routed to the Audio Processor IC pins 32 and 33. This IC has
internal gain adjustments for levels, filtering, and limiting. The output signal at Pin 35 is then
routed to U309 and U304 for deviation set and modulation balance. The output of balance
control U304B routes the audio to the RF board for FM modulation. The TX frequency
adjustment is made by U304C.
In receive, the raw discriminator audio from the RF board is routed to the audio processor IC at
Pins 28 and 29. The audio signal is processed by the audio processor IC for level and frequency
response. The audio output of the audio processor IC, Pin 38, is buffered then routed to audio
amplifier U307.
In receive, the discriminator audio is also sent to the DTMF decoder input, Pins 30 and 31, of the
audio processor IC. If a valid decode signal is detected, Microcontroller U301 will enable relay
control Q303 or Q304.
Other Analog Functions
To supply the proper voltages for the two boards, various voltage regulators are used. U311 is
used to produce +7.5 VDC for the RF board. U310, U312 and U313 are used to supply +5 VDC
and +3.3 VDC for the control/loader board.
9 HARDWARE OPTIONS
The DTX-165-RR-SIG 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 RELAY1 AND RELAY2 POLARITY
The default polarity for Relay1 and Relay2 is Normally Open.
To change the polarity of Relay1 to Normally Closed, remove R339 and place a 0ohm resistor for
MR340.
To change the polarity of Relay2 to Normally Closed, remove R343 and place a 0ohm resistor for
MR344.
9.2 RF BOARD OPTIONS
9.2.1 DISCRIMINATOR POLARITY
The polarity of the discriminator output at pin 9 of U102 is configured at the factory such that an
increase in RF frequency causes an increase in DC voltage. This is considered “normal” mode.
An inverted mode is available where an increase in frequency causes a decrease in voltage. This
is effected by removing R125 and placing it in the open pad pair denoted as MR130.