Unable to Tune TV to Sky + RF output

Question

I have a technica flat screen tv. If I do not connect an aerial to my Sky box I can tune the tv to sky via the RF output. If I then connect the aerial to the Sky box I lose the sky signal on the TV. I have tried tuning both the TV and DTV but still cannot tun into the Sky RF output. The Sky Receiver and TV are in separate rooms and so I cannot use the Scart Connector