Comtech EF Data DT-4500 Series - Manual (Page 100)

DT4500 Series Down Converters MN/DT4500.IOM
Theory of Operation Revision 1
82
The "Daisy Chain" configuration is designed to chain the IF output of up to twelve (12)
on-line converters together through RSM's terminating in a backup Converter. When a
fault occurs in an on-line converter, the RSM in the converter with the fault is
commanded to switch to the backup Converter. The backup Converter performs the fault
detection, self-reconfiguration and the logical switching functions. If the backup
Converter has a fault, it will not attempt to perform the protection-switching task. If the
backup Converter does not have a fault, it will assume the frequency and attenuation of
the faulted on-line converter, and compensate for the chain losses.
The backup Converter in the "Daisy Chain" communicates with the on-line converters
through a high speed (data interface) bus (HSB). When faults are detected, the backup
Converter re-configures itself to replace the on-line converter with the fault. The backup
Converter also uses the HSB to monitor configuration changes made to the on-line
converters 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 on-line units. The HSB does not interfere with the remote
control communications link for access to any of the converters in the "Daisy Chain".
The DT-4500 Series Down Converters are a standard 19 inch rack mounted units, 1.75
inches in height. The converter is 22 inches deep, and weighs 25 pounds. Prime power
the converter can be either 100 to 125 Vac, or 205 to 240 Vac, at 47 to 63 Hz (or
provided with an optional -48 Vdc prime power input). The power dissipation is 60
watts. The converter can operated in a temperature environment of 0 to 50 degrees C at
10,000 feet altitude in 0 to 95% relative humidity.
C.2 RF S
IGNAL
C
ONVERSION
As a typical example of the RF signal processing, the RF input to the DT-4512 Down
Converter is 12200 to 12750 MHZ at a typical level of -45 dBm. The RF is mixed in the
first mixer with a 13280 to 13830 MHZ synthesizer signal from a multiplier, in 125 KHz
fine tuning steps. The synthesizer is locked to a 5/10 MHZ reference oscillator. The first
mixer is located in the converter Signal Path Module, and the synthesizer consists of a
Coarse/Fine Step Module and a Sum Loop Module.
The intermediate IF is 1080 MHZ which is mixed in the second mixer with the1150
MHZ IFLO providing a +20 dBm, at 1 dB compression, 70 MHZ IF output. The second
mixer is also located in the converter Signal Path Assembly.
Figure 34 is a typical functional block diagram of the converter.