By Ann Saphir and Howard Schneider (Reuters) – Federal Reserve Chair Jerome Powell said this week he’s looking for compelling signs that inflation is cooling before the U.S. central bank will let up on what’s so far been its most aggressive set of interest rate hikes in decades. In data released on Friday, he largely got the opposite. Inflation by the Fed’s preferred measure, the personal consumption expenditures price index, jumped 6.8% in June, its steepest increase since 1982, and the rise in core prices – excluding food and energy prices and used by the Fed as an indicator of the inflation…