Demodulator
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.
glangsto@nrao.edu Last update: 98 January 16