Comtech EF Data DT-4500-A Series - Manual (Page 27)

DT-4500A Series Downconverters Revision 1
Introduction MN-DT4500A
1–3
1.2.1 Applications
The downconverter operates over the RF frequency range with a typical gain of 35 dB. The RF
output level is +10 dBm at 1 dB compression allowing the capability for longer cable runs to
compensate for splitting networks without adding options such as external line amplifiers.
The phase noise performance exceeds the Intelsat phase noise mask for IBS and IDR services by
more than 9 dB. This allows high capacity earth stations to add more demodulators and still
meet transmission standards. The close-in phase noise is also very low. This makes the
downconverter ideal for low bit rate digital circuits such as used in DAMA hub earth stations.
A selectable EIA-232C or EIA-485 remote control serial communications connector interface is
provided on the rear of the downconverter. All configuration control, status retrieval and
adjustments are available as ASCII commands through the serial interface, or as local operator
input command to the downconverter.
A detachable Input/Output Module (IOM) can be mounted in the rear of the downconverter
chassis for switching the RF output for single thread operations, or for testing the output of the
unit. The connectors for the IOM are located on the rear panel.
In applications where downconverters are "Daisy Chained" together to provide distributed
online protection switching to a backup downconverter, the IOM is replaced with a detachable
Transmit Switch Module (TSM). The TSM contains RF and IF transfer switches. Type N
connectors are provided for the RF loop, and 50 or 75 ohms BNC connectors are provided for
the IF loop.
The "Daisy Chain" configuration is designed to chain the IF output of up to twelve (12) online
downconverters together through RSM's terminating in a backup downconverter. When a fault
occurs in an online downconverter, the RSM in the downconverter with the fault is commanded
to switch to the backup downconverter.
The backup downconverter performs the fault detection, self-reconfiguration and the logical
switching functions. If the backup downconverter has a fault, it will not attempt to perform the
protection-switching task. If the backup downconverter does not have a fault, it will assume the
frequency and attenuation of the faulted online downconverter, and compensate for the chain
losses.
The backup downconverter in the "Daisy Chain" communicates with the online downconverters
through a high speed (data interface) bus (HSB). When faults are detected, the backup
downconverter re-configures itself to replace the online downconverter with the fault. The
backup downconverter also uses the HSB to monitor configuration changes made to the online
downconverters by either remote control or front panel command inputs.
Changes in frequency, attenuation or polarity are entered into the backup table as they are
made, as well as information from new online units. The HSB does not interfere with the remote
control communications link for access to any of the downconverters in the "Daisy Chain".