My RHT497H is equipped with a single Freeview tuner and the full range of Freeview+ features,
If I buy a dish or aerial do I need a receiver or is it built in to the equipment.
No, the tuner/receiver is built in. You just need to connect an appropriate UHF TV antenna pointed at your local Transmitter. As this PVR seems to have both analogue & digital tuners, you'll have to be careful to ensue it defaults to digital reception, if that's what you want to record.
John