Solar Outages
A solar or sun transit outage is an electromagnetic phenomenon wherein a station downlink is temporarily unable to receive a satellite signal due to interference from the sun as it passes behind the satellite. Solar outages occur on a predictable schedule and affect downlinks in the US for about five consecutive days, for as much as six minutes a day, twice each year. Every spring and fall, NPR Distribution posts a predicted sun outage schedule via DACS and on this page. Alternate feeds of affected program transmissions are also scheduled and can be chosen from the SOSS schedule as needed. If you have questions about an alternate feed, please contact Public Radio Services at 202.513.2600.
Earth Station Solar Transit Outage Predictions
The solar outage charts give specific dates for your location, broken down by state. Large states may be divided into several regions. The following rules apply to all solar outages:
The dates listed are those for which the solar disk will be within the beam pattern of your receive antenna. On these days you will see a definite reduction in performance as the sun passes. All stations will see a reduction of EbNo reading on the digital audio channels. If a downlink has enough margin, there will be no effect on the audio. If the downlink does not have enough margin, audio may be lost for up to several minutes. Stations with marginal downlinks may see some degradation one day before or one day after the days listed.
The times listed are for the peak of the interference. Depending on the size of your antenna, the interference may begin up to 4 minutes before this time and last up to 4 minutes after it. The interference will be longer on days in the center of the range.
The times are given in NPR network time, which is Eastern Standard Time for the spring, and Eastern Daylight Time for the fall.
These predictions are based on a standard 365-day year. The variations from year to year are so small that separate predictions for each year are not necessary.
- Stations may want to set up one or more of their ComStream ABR 700s to monitor the performance of their downlink during solar transit. To do this, you should:
- Reset the MINIMUM EbNo and MAXIMIM EbNo registers of the ABR 700 and log them each day after the solar transit.
- Reset the FADE and SYNC LOSS counters of the ABR 700 and log them each day after solar transit.
The degree of interference depends, among other things, on the bandwidth that the receiver is using at the time. This suggests that monaural programs would have a 3 db advantage over stereo programs at the time of solar transit.