Ann Wester
Ann Wester
The NRAO OVLBI tracking station design was done primarily by Larry D'Addario, with the help of Ray Escoffier, Bill Shillue, Dick Thompson, and Dan Pedtke. Dave Burgess, Tim Glasser, Dave Gordon and Ann Wester constructed the system with the help of many others at NRAO Green Bank and other sites.
The satellite commuications modules were designed and constructed by NRAO personel. The IF electronics design has many similarities to the NRAO VLBA electronics design.
The Block diagram for the system is presented below, with detailed descriptions of each module.
Below the IF downlink spectrum is shown for the normal VSOP downlink. The full width of the spectrum is 500 MHz, and the maximum in the spectrum is at 600 MHz.
The Demodulator performs two major functions; 1) recovering the digital I, Q and Clock signals from the downlink carrier, and 2) generating a recovered carrier signal from the downlink signal containing the data. The Demodulator input is from the downconverter, and for VSOP, the IF center frequency is at 600 MHz. The digital data are provided to the Decoder in the equipment trailer and the recovered carrier is provided to the Two Way Timing Control Module.
The Two Way Timing (TWT) Control Module recieves uplink and downlink frequency predictions from the station computer once a second. The TWT micro processor re-calculates the uplink and downlink frequencies for two DDS boards 5000 times a second. The downlink frequency is only used internaly. The TWT phase detectory compares the predicted downlink frequency with the recovered carrier from the demodulator. These measurements are filtered in the TWT control module and 10 measurements per second of the residual phase are provided to the station computer.
The uplink frequency is provided to the TWT Transmitter module where it is up-converted and amplified. The TWT Control Module consists of 7 major sub-assemblies.
The VME rack contains the station computer, MCB interface, decoder boards and optical modem.
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