Radeng is right. In the process of receiving, receivers "transmit" a low-level RF signal that can cause interference. I understand the BBC uses this phenomenon to detect if a television is on in a home, for tax purposes.
That may once have been true...but nowadays the BBC just seem to make the assumption that all addresses should have a TV licence (making the assumption that every house must have a TV
). Rather than actually bothering to check whether an address actually has a TV or not
.