Microcom Design ucom DAMS-NT DigiRIT, Operation Manual, Page: 7 / 40

Release 1 DAMS-NT DigiRIT Operation Manual 12/14/2012
Microcom Design, Inc. 6
1.3. Theory of Operation
A typical Microcom DAMS-NT DigiRIT system diagram is shown in Figure 2. The ground
elements consist of a parabolic satellite antenna (or dish) complete with a GOES compatible
“front-end” or “feed”, the Microcom DAMS-NT DigiRIT Receiver, and the user’s computer
system. The space portion of the system is either the GOES-East or GOES-West satellite.
The LRIT signal originates at WCDA and is simultaneously broadcast to both the East and West
GOES satellites. The LRIT signal consists of several GOES products including the Emergency
Management Weather Information Network (EMWIN) alerts and notifications, various imagery
products, and the DCS re-broadcast. The DCS re-broadcast portion includes all messages
received by NOAA at WCDA.
The parabolic antenna receives the LRIT signal and focuses it on the “front-end”. The downlink
frequency of the LRIT signal is 1694.000 MHz, which is in the RF L-Band. Transmission in the
L-Band spectrum are relatively immune to weather fading and are not significantly affected by
cloud cover or rain storms.
The “front-end” or “feed” consists of a block down convertor and a low-noise amplifier (LNA).
Often the front-end is simply referred to as an LNA. The block down convertor translates the L-
Band signal to a lower frequency IF and the LNA boosts this signal before it is sent to the
DigiRIT Receiver. The DigiRIT Receiver can accept a wide range of IF frequencies so it is
compatible with numerous front-ends. Front-ends typically require a DC supply to operate and
the DigiRIT Receiver is capable of supplying 12 VDC over the same coaxial cable that returns
the IF signal.
GOES Satellite
(East or West)
Parabolic Parabolic Parabolic Parabolic
Antenna Antenna Antenna Antenna
With
With With
With
Front Front Front Front----End End End End
Microcom DAMS Microcom DAMS Microcom DAMS Microcom DAMS----NT NT NT NT
DigiRIT Receiver DigiRIT Receiver DigiRIT Receiver DigiRIT Receiver
User Supplied Network Switch
User Supplied Network Switch User Supplied Network Switch
User Supplied Network Switch
User Supplied Server User Supplied Server User Supplied Server User Supplied Server
Common Common Common Common
Coax Coax Coax Coax
Private LAN Private LAN Private LAN Private LAN
Connection Legend
50 Ohm IF
DAMS-NT TCP/IP
DC Power
RF Signal
Digital or KVM
Figure 2: Typical DigiRIT System Block Diagram
The DigiRIT Receiver has two mutually exclusive IF inputs. One input is designated the 70
MHz IF Input and can accept a signal in the range of 50 to 90 MHz (70 ± 20 MHz). The second
input is the 140 MHz IF Input and covers a range from 126 MHz to 154 MHz (140 ± 14 MHz).
Only one of these inputs can be specified as the active input. Both inputs are capable of sourcing
a DC supply for the front-end. In most cases, the IF signal delivered by the front-end includes
both the raw DCS spectrum and the LRIT transmission, as well as numerous other GOES RF