I would have thought that your recorder would have it's own tuner built in. You should actually be able to record without it being attached to a TV, though of course you would need one connected when you set up the recording. Have you plugged the aerial lead into the TV instead of the recorder? If you have the aerial in the recorder then I suggest you do a re-scan for programs in case it has lost it's program information.
Surface Pro (2017) vs Surface Pro 4