Station Diagnostic Software

Extensive diagnostic and plotting software is used to analyze the satellite data and timing links. The diagnostic software is divided into three major groups,
Log Analysis
Extraction and display of station monitor data, such as temperatures, LO levels, timing offsets, etc.
Phase Residials
understand the properties of the offset between predicted and measured downlink frequency allows measurement of many system parameters. The magnitude of the difference measures the error in the satillite orbit. The RMS of the frequency difference measures the quality of the link. Smooth, but short term, variations in the frequency offset, is indicative of problems with stability of some station hardware component.
Telemetry Data
VSOP/HALCA downlinks a large volume of data recording satellite status. In particular, the uplink power recieved and the frequency offset from nominal are repored. Also the state of the on-board astronomy systems is reported.

Log Processing

The primary program for analyzing the station logs is "logRead", which allows extraction of selected log entries. Plotting scripts have been written which use logRead output to present log data in a convenient form.


The program logRead can produce an ascii listing of selected types of log entries. Any of the three main type of log entries may be choses, Events, Anomalies or Monitor data. The program allows data to be selcted by time range and also the output format can be specified.


The vsop downlink power is plotted with script vsopDownPlot. The downlink signal (in Kelvins) is plotted versus truncated MJD. An example for experiment VT136 is shown below:

Phase Residual Processing

The primary program for analyzing the phase residual data is "twtPlot". The twtPlot program allows selection, fitting and averaging of phase residual data. This program takes a binary residual phase file and produces an ascii listing of the data.


The script residualPhasePlot runs the twtPlot program for a selected tracking pass and produces three plots:
Residual Phase
Difference between predicted and measured downlink phase during the tracking pass. Each time the downlink is lost, the residual phase count is reset to zero.
Residual Frequency
The residual frequecy is calculated by a fit to the slope of the residual phase data over a two second period.
RMS Frequency
The RMS after subtracting the linear model to the phase data.
Below are the plots for the tracking pass for experiment VT136.

Telemetry Processing

The program "vsopCheck" extracts telemetry header data from the realtime logs for display.


The script "vsopLinkPlot" runs vsopCheck to plot the "AGC" level of the HALCA/VSOP link. This level is a function of both the stability of the uplink signal frequency and the uplink power level.

orbit error estimation

Under the assumption that all of the orbit error is along the trajectory of the orbit, we can estimate the error in the orbit. This is done with the script "orbitErrorPlot". This estimation of the orbit error is useful for the MIT Near Real Time Correlator. "orbitErrorPlot" also fits a polynomial to the phase residuals and plots the residual to the fit so that fluctuations in the two-way timing link with VSOP can be studied. Below are plot of the residuals to the two fits done by "orbitErrorPlot".

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: 97 July 7