"But, on the downside, some of our panel experienced problems at night
- and we saw these effects in our measurements as well. The problem
will be familiar to many listeners to medium-wave: at night, changes
in the atmosphere mean that signals from distant transmitters reach
our shores more easily. On medium-wave, you might hear this as cross-
talk: a foreign voice underneath what you're trying to listen to, or
the occasional 'splat' of another transmission. The issue we came
across with DRM is that this interference causes the radio to stop
decoding the signal: sometimes only momentarily, sometimes for a while
longer. So rather than listening through the interference, it's like
all digital systems: you either get it (and so get it at a
consistently high quality) or you don't get it at all. So while most
of the panel continued to listen without experiencing any problems,
some of them found they were only served during the day and had patchy
coverage at night. And of course this problem became worse as the
hours of daylight shrunk during the autumn; so by winter, some were
beginning to experience poor reception in the late afternoon."

http://www.bbc.co.uk/blogs/radiolabs...&ssoc=register