The OVLBI Demodulator performs two main functions; 1) extracting the I, Q and Clock from the QPSK modulated satellite downlink and 2) recovering the downlink IF carrier frequency. The I, Q and Clock signals are sent down to the OVLBI Decoder in the equipment trailer. The IF carrier frequency is output to the TWT control module.

The exploded view of the Demodulator, above, shows Costas Loop Control Board to the left, Interface board to the right, Carrier Phase Lock Loop assembly 3 to the middle left and the MCB interface removed from the center of the module and placed above the demodulator. The Demodulator is composed of 7 major sub-assemblies, described below:

MCB Interface (No Photo)

Control of the Demodulator is via the standard VLBA MCB interface. The IF center frequency for the downlink is communicated via the MCB. The Demodulator reports Clock and Costas Loop Lock and other status info via the MCB. Because this sub-assembly is unchanged from the VLBA design, and used in most OVLBI modules, it is described elsewhere. Two spares are in stock.

Costas Loop Control Board

One spare needed, none assembled.

Interface board

One spare needed, none assembled.

Carrier PLL Module

This module regenerates the downlink carrier tone for use by the TWT control module. One spare needed, none assembled.

Related Web Sites

Return to the OVLBI Hardware Page or the OVLBI Home Page. VSOP/HALCA has a home page. The VLBA Correlator NRAO Socorro is developing other hardware and software for the NASA OVLBI project. There is a Space VLBA Correlator home page as well.

Return to the Station Software Guide. The National Radio Astronomy Observatory (NRAO) is a facillity of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.
Last update: 98 January 16