[Radio Wrangler]

Medium wave transmitters as such, no.

Usually 'Transmitter' is used to describe something which covers some degree of range, either for communicating point to point or for broadcasting. Doing so intentionally puts it squarely under the wireless telegraphy act, and it needs a licence from Ofcom. Without this you would be treated as a pirate broadcaster, and the penalties are scaled to be hard-hitting for commercial operations.

At the other end of the scale, it is quite usual for people to have signal generators to test and evaluate radios with. These can be modulated with whatever audio you want. Normally they are connected to the external aerial socket of a radio, but not all radios have these. Plenty of sets have internal aerials, either as a frame wound with wire, or the common ferrite rod type. To test these radios, it is necessary to feed your signal generator into a coupling coil, or antenna wire fairly close to the set.

Some people do this more to listen to the set than to do formal tests. Rather than tie up an expensive bench instrument, they build small single-purpose units. The aim is to not have any detectable amount of signal beyond their own property. The name they go by is odd, and I've never come across the reason. Search for "pantry transmitter" and you'll find them. It might have been better if they'd been called test sources, or something like that, without invoking the T-word.

David