6–1
Chapter 6. THEORY OF OPERATION
This chapter contains a general description of the theory of operation for the XSAT downconveter
and upconverter sections. The XSAT can be used for SCPC, DAMA AND TDMA, as well as for
full transponder HDTV and analog TV, applications.
The description in this section is for the standard 25Watt transceiver. For other models,
refer to Chapter 2. Specification, for the correct frequency, gain, and output power levels
associated with it. In all models, the downconverter and upconverter local oscillators are
independently synthesized to allow simplex or duplex operation. In order to minimize
complexity, they share a common power supply, an internal high stability 10 MHz reference
oscillator, and the Maintenance and Control (M&C) unit
.
The downconverter section operates in the frequency range of 7250 to 7750 MHz, with a
temperature compensated gain of 45 dB. This high level of gain provides an IF output signal
level of +13 dBm at 1 dB of gain compression. This provides the capability to handle longer
modem cable runs, or fan out for splitting networks without requiring additional line amplifiers.
The upconverter section operates over a frequency range of 7900 to 8400 MHz with a
temperature compensated gain of 71 dB.
For 25W Transceivers: The RF output level is +44 dBm minimum at 1 dB gain compression
over the operating temperature range.
The phase noise performance of both the upconverter and downconverter sections exceeds the
Intelsat phase noise mask for IBS and IDR services by 6 dB. This allows phase dependent
demodulators to provide the best possible performance. The close-in phase noise is also very low
making the converter ideal for low data rate applications such as DAMA hub earth stations.
An auto select RS-232 or RS-485 pin out is available in the circular COM connector on the
exterior of the chassis. All configuration control, status retrieval and unit adjustments are
available as ASCII commands through this interface.
