In just two weeks, on Dec. 8, the Federal Communications Commission will set in motion a series of events that could well change the face of television in America and indeed of the entire media marketplace.In what’s known as a spectrum auction, the FCC is offering TV station owners huge sums of money to sell back their broadcast franchises so the agency can then resell those frequencies to wireless giants such as Verizon and AT&T to vastly build out their networks.The big question is how many station owners will take the FCC up on the offer.No one knows. It won’t be known until sometime next spring, when the results of the auction are announced.But we can tell you this. If a lot of stations sign on, the effects would be massive.Stations would close across the country, leaving some markets with just one or even none. Viewership numbers would tumble, as would TV ad dollars. We’d see a shift of advertisers to other media: Digital, radio, local cable, out of home and maybe even newspapers.By contrast, if only a few stations take up the FCC on its offer, the effect will be minimal.To show how all this could play out, Media Life looks at one market, San Antonio. We’ve crafted three scenarios: light participation in the FCC auction, moderate participation and full participation.We’ll then estimate the impact of each scenario on total viewership, share of viewership, TV ad spending, cost of TV air time, levels of cable/satellite subscriptions, and shifting of ad dollars to other media.