On Friday, 24 January 2020 13:47:19 UTC, Dave Plowman (News) wrote:
In article ,
Bill Wright wrote:
On Thursday, 23 January 2020 14:19:49 UTC, Dave Plowman (News) wrote:
However, many portable radios will exhibit multi-path just with a
person moving about in the same room.

That's really better described as the standing wave pattern in the room
changing.

Oh, indeed. But the audible results are similar.

For VHF FM, a standing wave causing complete or near-complete signal cancellation obviously results in what is effectively weak or zero signal at the receiver. You'd expect degradation into noise pure and simple but there's usually another weak signal path from a reflection external to the room. With the direct path almost or completely cancelled out that signal becomes more significant so the audible result is often the high frequency audio distortion (lisping) that is also caused by simple signal reflections.
In the case of analogue TV, standing waves within the room (or loft)can, by the same mechanism, cause ghosting rather than simple weak signal.

Bill