Ivor & Mastercraft:
Henry is a regular poster, who definitely does not 'take the urine'. Not everyone understands technology that well!
Henry:
Television transmitters are designed to ensure that viewers can get a good signal by using an external (roof-mounted) aerial. They are not designed to provide a decent signal without such an aerial.
However many people can get a reasonable signal by using the built-in aerials that are normally provided with portable TV sets, simply because they happen to live fairly close to a powerful transmitter.
So location is all important. (There's absolutely no way I would be able to get any sort of signal at all, just using a portable TV's built-in aerial or even a big loft-mounted aerial, where I live - which is well away from a transmitter; it's only a big outdoor aerial that will work here. However I've used portable TV sets - just with their built-in aerial - in other parts of the country and obtained good reception).