Try a booster.
I bought one in LIDL some months back and it does an OK job. I would assume that if I paid more that I would get a better result. It plugs in to an electrical socket and has one co-ax in and 2 co-ax out ports.
I know Power City have them but don't know how good they are. Somewhere like Maplins or Peats could have a better range of choice.