LCD TV picture freezes?

My friend has moved to another property and connected her lcd tv to the existing outside roof ariel, when viewing, the picture freezes for a few seconds only but does this several times an hour.The set has built in freeview but this happens on all channels. At her previous property she only had an indoor ariel and was unable to obtain freeview or channel 5 but had no problem with the picture freezing. Is there a simple check to find out if it is a reception problem ?