tony sayer writes:

There is a system where crystal place relays Wrotham with something like
a 384 odd kHz offset there is a BBC engineering paper on it somewhere!..

It's here -- "THE CRYSTAL PALACE FM FILLER EXPERIMENT" (great title
for a sci-fi horror film, that):
http://downloads.bbc.co.uk/rd/pubs/reports/1996-06.pdf

--
Adam Sampson http://offog.org/