Anyone out there know what XC & SC & asterix next to the yellow highlighted frequencies on the ZOB chart mean
Yeah that's my chart I put together, I should have included a legend on what my various notes mean. The XC does mean frequency "cross-coupling". In this case 132.825 has been observed cross-coupled with 125.075 when the two sectors are combined, ZID77 and ZID87.
Just to add to ATCTech's great explanation, my understanding is in the US they only have the capability to cross-couple two frequencies together, unlike Canada where multiple frequencies can be coupled. It also seems to be a controller option, some use it while other don't (for some reason).
I wonder if "SC" means simulcast, meaning same controller but no coupling.
That's exactly what it means. The * beside 135.375 indicates it's only used when the sector is open or as required. So in this case when ZOB46 is combined into ZOB45, 120.325 covers both (for aircraft) but the controller can still be heard "simulcasting" on 135.375. The chart is a bit dated so it's possible the two frequencies can now be cross-coupled which would make the SC redundant. I just have not been able to confirm it yet ?
BTW in the sector adjacent to the east, ZOB58, the R beside the box indicates the frequency is rarely used but the controller can still be heard simulcasting (SC) on 121.075. The arrow pointing up beside ZOB59 means 119.725 is used to cover the sector above.
The intent of the chart is to show typical configurations during the day shift. The chart boundaries are based on official sector charts. The frequencies and notes are based on observations from various sources so may not be up to date or cover all possible configurations. As this information is always changing any updates heard or feedback on accuracy always appreciated. When I have time I'll post an updated chart with a legend explaining the notes.
AS