Troubleshooting DOMSAT


The real-time status page for the LRGS shows hourly statistics for the most recent 8 hours. If you notice that your DOMSAT system is not receiving data, it may be for one of several reasons. This article will help you determine what component is failing, and what you can do to correct it.
On the rtstat screen, a properly functioning DOMSAT system should look like this:


The first line of hourly statistics shows the number of messages received over DOMSAT. Two numbers are shown indicating good messages and messages with one or more parity errors. Parity errors are not caused by DOMSAT and do not indicate a DOMSAT failure.
The second line indicates the number of messages dropped by the DOMSAT link. Dropped messages are detected by gaps in the DOMSAT sequence number. If this number becomes large it could indicate a marginal DOMSAT signal or other problem. A few messages every hour is not a concern, especially during inclement weather.
The area below the hourly columns shows more detail. Find the line for DomsatRecv. It will show you the last time a message was received over DOMSAT, what its sequence number was, and what state your DOMSAT software is in. It should normally be "Active". Other possibilities are:

The following figure shows your DOMSAT hardware. Any one of these components (including the cables) can fail.


The first thing to check is the DOMSAT system at Wallops. Point your rtstat program to drot.wcda.noaa.gov and connect as your NOAA-supplied user name. If the DROT system at Wallops is experiencing similar problems to you, contact NOAA. If the NOAA system is okay, then the problem is with your own ground system.

Look at the receiver. If the SYNC light is off or red:

If you can measure 18v DC, this would indicate a failure of the LNB or (more likely) that your antenna has been knocked out of alignment. A replacement LNB costs about $400. There are likely antenna contractors in your area that can check the alignment and install the LNB replacement.

If you do not see 18v on the line, attempt to measure 18v directly at the back of the receiver. If you do see 18v DC at the receiver but not at the LNB, this indicates a failure of the coaxial cable. Replace it.

‚ÄčIf you do not see 18v at the receiver, this would indicate either a misconfiguration or failure of the receiver. Has the receiver configuration been changed recently? Check to make sure that 18v DC is enabled. If it is and you still can't measure 18v, then your receiver will likely need to be replaced. Contact your supplier.

Suppose your receiver is in sync. Check the cabling from the data port of the receiver to the Sangoma board installed inside the DOMSAT PC. Has it been moved, damaged, or disconnected? This is a custom cable provided by Sangoma Corporation. The newer boards have a Y-cable connecting to the board. Make sure that the cable to the receiver is plugged into port 1.

If all of the above looks good and you still are not receiving DOMSAT, contact your software supplier for further assistance.


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