Release 1
DAMS-NT DigiRIT Operation Manual
12/14/2012
Microcom Design, Inc.
19
2.2.1.6.
140 MHz Test Connector
The 140 MHz IF Test connection provides a buffered output of the 140 MHz IF Input signal, if
one is present. This test connector is primarily provided to allow an easy connection point for
monitoring the 140 MHz IF on a Spectrum Analyzer.
Note that even when DC power is provide to the 140 MHz Antenna Input, the DC is NOT
present on the 140 MHz Test connector.
2.2.2.
Rear Panel Connections, Controls and Indications
The Rear Panel of the DigiRIT primarily provides the operational connection points for the unit.
However, a few additional controls and indicators are also included on the Rear Panel as shown
in Figure 4.
2.2.2.1.
70 and 140 MHz Antenna IF Groups
As discussed in Section 1.3, the DigiRIT Receiver can utilize either a 70 MHz (±20 MHz) or a
140 MHz (±14 MHz) IF input. Located on the Rear Panel are two similar groups of two
connections and an indicator LED that are identical in their functionality, except for the
aforementioned operating frequency.
Generally speaking, the 70 MHz IF is utilized when adding a DigiRIT Receiver to an existing
Microcom DRGS installation, while the 140 MHz IF is used in a stand-alone LRIT system.
The DigiRIT Receiver will accept an input signal range of –90 to –20 dBm. However, the
nominal signal presented to the demodulator circuitry should be between –90 to –50 dBm. As
such, if the nominal input signal is above –50 dBm then input attenuation (see 3.1.3) should be
used to reduce signal strength presented to the demodulator.
2.2.2.1.1.
Antenna In
The 70/140 MHz Antenna In requires a cable terminated in a male SMA connector. The SMA
connector’s integral screw threads ensure a secure connection. The antenna input signal will
typically come from a satellite dish’s front-end or feed. In addition to the GOES LRIT signal,
several other GOES signal components will most likely be present in the input.
The DigiRIT’s Antenna In can also provide DC power to an external feed or dish front end. See
Section 1.3.4 for cautions and additional information on using the DigiRIT to power the front
end. When DC power is present at the 70/140 MHz Antenna In connection, the associated power
LED will be illuminated.
When first installing the DigiRIT receiver it is recommended to first power up the unit
WITHOUT a cable connected to the Antenna In to determine whether DC Power is present
or not. If DC Power is present and the Antenna In is not being connected to a satellite dish
front-end, re-configure the unit to remove the DC Power (see Sections 3.1.4 and 3.2.2.1)
before proceeding. Once the state of the DC Power is established, and corrected if
necessary, power down the unit and complete the connections.
2.2.2.1.2.
Antenna IF Out
The Antenna IF Output provides a buffered output of the 70/140 MHz IF input similar to that
provided on the Front Panel (see Sections 2.2.1.5 and 2.2.1.6). The primary purpose of this