High/Low Power
If RNet compatibility mode is not programmed into the unit, high and low power levels can be
programmed into the unit on a channel by channel basis. High power is selected by placing the CSN input
at a logic high state. Placing the CSN input at a logic low state chooses low power. The CSN input has an
internal pull-up resistor; it will assume the high state and the module will be set for high power when left
unconnected.
Specialized Modem Operation
Modems designed to achieve the highest data rates possible in a radio channel may require a direct DC
connection to the modulation path and the removal of the limiter-filter. In order to receive FCC
Certification, the DTX module must either be tested and approved with a specific modem connected to the
transmitter, or a modulation limiter and limiter-filter must always be present in the transmit modulator
audio path with the modulation inputs AC coupled. To allow for the most flexibility for the end user, the
unit was certified as a stand-alone unit. It is possible, with hardware modifications and special
programming software (not supplied with the unit), to DC couple the AUX IN input and/or defeat the
limiter-filter. The modulation limiter would still be in place, but the deviation of the DTX module could be
set such that the modulation limit within the DTX module is never reached. The deviation would be set by
the modem level and the AUX IN gain setting. The end user/system integrator would then bear the
responsibility of obtaining certification or operating in a frequency band where certification is not required.
Contact RITRON for details.
Note: Most modems will connect directly to the DTX without requiring
any special modifications or programming.
Antenna Placement
The DTX module is enclosed in a metal housing for RF shielding. However, RF emitting sources located
very close (less than 12 inches) to the unit can at times affect its operation. It is not recommended that an
antenna be connected directly to the module’s BNC connector unless the RF output power is set for less
than 2 watts or the module is placed within another RF-tight enclosure.
5.6
RNET COMPATIBILITY MODE
The DTX module can be programmed to mimic some of the behavior of the RNet 450 radio. In the RNet
compatibility mode, the CSN input is used as a channel selector line. A logic low selects channel 1 while a
logic high selects channel 2. The channel select lines, CS0, CS1, and CS2 have no effect. Also, the DCD
output is held in its true state during transmit. It would normally be false in transmit.
