Several affiliate stations have come to us with concerns about their XDS Receivers, citing a low EbNo and a lack of IP Backup, even when their network has the fallback enabled on their receivers. Even more confusing, these issues don't arise on their other XDS receivers pointed at the same bird.
What is going on, and how can the affiliate fix it?
Brian Anderson, head of the OMNi Network Operation Center, let me know that this is an issue that his staff has encountered frequently since the move from AMC-8 to SES-11. Nine times out of ten, the issue is polarity. Brian was kind enough to answer my questions about this new and confusing receiver issue.
What are the telltale signs that a receiver is suffering from a polarity issue?
Some receivers run a very acceptable EbNo while others read much lower – streaming will not “kick in” with RF being intermittent.
What causes this issue to occur?
The large change in orbital slot position, AMC 18 was at 139 degrees West while AMC 18 (now SES 11) is at 105 degrees west. On the initial Satellite repoint many just repointed the antenna not realizing that the skew changed drastically (around 40 degrees on many downlink locations, dependent on your location in the US).
The radio industry was spoiled in a way over the years using the 139 degree orbital position, although look angles were much lower (especially in the eastern US) the absence of a neighboring satellite on both sides meant most radio station could get away with older non 2 degree compliant antennas without being affected. Today with neighbors on both sides, pointing and polarity become more critical (probably more so with antennas that were not ever designed for 2 degree separation of satellites).
Why does this affect only their OMNi receiver and not their Westwood receiver, or vice versa?
OMNi and Westwood are more affected because of carriers near the same frequency on the opposite polarity of the satellite. They are so many radio stations still running on 30 to 40 year old antennas ultimately not designed for today’s 2 degree separation of satellites. For those who are familiar with emissions testing on cars, think of trying to get a 40 year old vehicle to pass emission testing.
What can affiliate stations do to fix the issue?
With multiple receivers, including OMNI receiving signal, they should be able to adjust polarity until the weaker EbNo’s are as high as possible, this should not affect any other EbNo’s. caution , some older antennas are not equipped with full range polarity adjustment.