Microwave Data Systems MDS 4310, Installation, Operation & Field Maintenance

Page: 41 / 129

2-14 INSTALLATION MDS 05-2415A01, Rev. A
the transceiver or in the MDS 4350/MDS 4355 packaged system, provided a
complementary Interface/Utility board is installed in the MDS 4350/MDS 4355.
The following is a general discussion of modem interface signaling.
The Role of the Modem
The purpose of the modem is to convert RS-232 data passing through the external
INTERFACE
connector into digital signals that will modulate the transmitter, and to convert
signals recovered from incoming radio signals into RS-232 data. The modem is also
responsible for accepting RTS (Request To Send) from the
INTERFACE
connector and for
acknowledging transmitter operation with a CTS (Clear To Send) signal through the
INTERFACE
connector to the attached equipment.
RTS and CTS Signals
When RTS on the
INTERFACE
connector goes high, the transmitter is keyed by the RTS
line connected to the modem. Whenever the transmitter is keyed, a timer is started that
will, after a programmed time period, raise the CTS line at the
INTERFACE
connector. This
CTS time delay allows time for the transceiver’s transmitter and the master’s modem
circuitry to stabilize before data can be sent to the master station. CTS is programmable
in 1 ms increments within the range of 5 to 255 ms. MDS recommends a minimum of 10
ms of CTS delay for optimum system performance. Thus, 10 ms is the factory default.
When RTS goes low, the transmitter is unkeyed and CTS is set to low.
DCD Signal
When the squelch circuit in the receiver senses the presence of a carrier, the DCD line
goes high. When the squelch circuit in the receiver senses the lack of a carrier, the RXD
output is forced to a “Mark” condition and the DCD signal is set low. RXD and DCD are
signals on the
INTERFACE
connector.
POWER REQUIREMENTS
The MDS 4310 Transceiver can be powered from any source with a nominal terminal voltage
between 12 and 15 volts direct current and capable of supplying a minimum of 2.5 amperes.
NOTE
Under no circumstances should the nominal supply voltage
drop below 10.5 volts or rise above 16.5 volts. The supply must
be sufficiently regulated to limit any change in its output
voltage to one volt or less when the transceiver alternates
between transmit and receive.
The power output is factory adjusted for 5.0 watts at 13.8 volts. If the actual supply voltage is
not 13.8 volts under load, the transceiver’s power output should be adjusted to 5.0 watts
before the unit is put into service.
One approach to powering the MDS 4310 Transceiver from a 120 Vac source and providing
for backup power during power outages is to float charge a 12 volt storage battery from a
regulated 13.8 Vdc power supply. The radio can then be connected directly across the battery
terminals. The power supply should be equipped with current limiting to protect it in the
event the battery becomes deeply discharged during a long outage.